Merge pull request #8084 from jtattermusch/throw_rpcexception_on_failure

Fix wrong exceptions being thrown on send failure.
diff --git a/BUILD b/BUILD
index cd334b2..8109549 100644
--- a/BUILD
+++ b/BUILD
@@ -51,6 +51,7 @@
     "src/core/lib/support/backoff.h",
     "src/core/lib/support/block_annotate.h",
     "src/core/lib/support/env.h",
+    "src/core/lib/support/mpscq.h",
     "src/core/lib/support/murmur_hash.h",
     "src/core/lib/support/percent_encoding.h",
     "src/core/lib/support/stack_lockfree.h",
@@ -79,6 +80,7 @@
     "src/core/lib/support/log_linux.c",
     "src/core/lib/support/log_posix.c",
     "src/core/lib/support/log_windows.c",
+    "src/core/lib/support/mpscq.c",
     "src/core/lib/support/murmur_hash.c",
     "src/core/lib/support/percent_encoding.c",
     "src/core/lib/support/slice.c",
@@ -176,6 +178,7 @@
     "src/core/lib/http/httpcli.h",
     "src/core/lib/http/parser.h",
     "src/core/lib/iomgr/closure.h",
+    "src/core/lib/iomgr/combiner.h",
     "src/core/lib/iomgr/endpoint.h",
     "src/core/lib/iomgr/endpoint_pair.h",
     "src/core/lib/iomgr/error.h",
@@ -331,6 +334,7 @@
     "src/core/lib/http/httpcli.c",
     "src/core/lib/http/parser.c",
     "src/core/lib/iomgr/closure.c",
+    "src/core/lib/iomgr/combiner.c",
     "src/core/lib/iomgr/endpoint.c",
     "src/core/lib/iomgr/endpoint_pair_posix.c",
     "src/core/lib/iomgr/endpoint_pair_windows.c",
@@ -567,6 +571,7 @@
     "src/core/lib/http/httpcli.h",
     "src/core/lib/http/parser.h",
     "src/core/lib/iomgr/closure.h",
+    "src/core/lib/iomgr/combiner.h",
     "src/core/lib/iomgr/endpoint.h",
     "src/core/lib/iomgr/endpoint_pair.h",
     "src/core/lib/iomgr/error.h",
@@ -708,6 +713,7 @@
     "src/core/lib/http/httpcli.c",
     "src/core/lib/http/parser.c",
     "src/core/lib/iomgr/closure.c",
+    "src/core/lib/iomgr/combiner.c",
     "src/core/lib/iomgr/endpoint.c",
     "src/core/lib/iomgr/endpoint_pair_posix.c",
     "src/core/lib/iomgr/endpoint_pair_windows.c",
@@ -915,6 +921,7 @@
     "src/core/lib/http/httpcli.h",
     "src/core/lib/http/parser.h",
     "src/core/lib/iomgr/closure.h",
+    "src/core/lib/iomgr/combiner.h",
     "src/core/lib/iomgr/endpoint.h",
     "src/core/lib/iomgr/endpoint_pair.h",
     "src/core/lib/iomgr/error.h",
@@ -1047,6 +1054,7 @@
     "src/core/lib/http/httpcli.c",
     "src/core/lib/http/parser.c",
     "src/core/lib/iomgr/closure.c",
+    "src/core/lib/iomgr/combiner.c",
     "src/core/lib/iomgr/endpoint.c",
     "src/core/lib/iomgr/endpoint_pair_posix.c",
     "src/core/lib/iomgr/endpoint_pair_windows.c",
@@ -1258,6 +1266,7 @@
     "src/core/lib/http/httpcli.h",
     "src/core/lib/http/parser.h",
     "src/core/lib/iomgr/closure.h",
+    "src/core/lib/iomgr/combiner.h",
     "src/core/lib/iomgr/endpoint.h",
     "src/core/lib/iomgr/endpoint_pair.h",
     "src/core/lib/iomgr/error.h",
@@ -1370,6 +1379,7 @@
     "src/core/lib/http/httpcli.c",
     "src/core/lib/http/parser.c",
     "src/core/lib/iomgr/closure.c",
+    "src/core/lib/iomgr/combiner.c",
     "src/core/lib/iomgr/endpoint.c",
     "src/core/lib/iomgr/endpoint_pair_posix.c",
     "src/core/lib/iomgr/endpoint_pair_windows.c",
@@ -1541,6 +1551,7 @@
     "include/grpc++/impl/codegen/service_type.h",
     "include/grpc++/impl/codegen/status.h",
     "include/grpc++/impl/codegen/status_code_enum.h",
+    "include/grpc++/impl/codegen/status_helper.h",
     "include/grpc++/impl/codegen/string_ref.h",
     "include/grpc++/impl/codegen/stub_options.h",
     "include/grpc++/impl/codegen/sync.h",
@@ -1600,6 +1611,7 @@
     "include/grpc++/impl/codegen/service_type.h",
     "include/grpc++/impl/codegen/status.h",
     "include/grpc++/impl/codegen/status_code_enum.h",
+    "include/grpc++/impl/codegen/status_helper.h",
     "include/grpc++/impl/codegen/string_ref.h",
     "include/grpc++/impl/codegen/stub_options.h",
     "include/grpc++/impl/codegen/sync.h",
@@ -1660,6 +1672,7 @@
     "src/core/lib/http/httpcli.h",
     "src/core/lib/http/parser.h",
     "src/core/lib/iomgr/closure.h",
+    "src/core/lib/iomgr/combiner.h",
     "src/core/lib/iomgr/endpoint.h",
     "src/core/lib/iomgr/endpoint_pair.h",
     "src/core/lib/iomgr/error.h",
@@ -1767,6 +1780,7 @@
     "src/core/lib/http/httpcli.c",
     "src/core/lib/http/parser.c",
     "src/core/lib/iomgr/closure.c",
+    "src/core/lib/iomgr/combiner.c",
     "src/core/lib/iomgr/endpoint.c",
     "src/core/lib/iomgr/endpoint_pair_posix.c",
     "src/core/lib/iomgr/endpoint_pair_windows.c",
@@ -1938,6 +1952,7 @@
     "include/grpc++/impl/codegen/service_type.h",
     "include/grpc++/impl/codegen/status.h",
     "include/grpc++/impl/codegen/status_code_enum.h",
+    "include/grpc++/impl/codegen/status_helper.h",
     "include/grpc++/impl/codegen/string_ref.h",
     "include/grpc++/impl/codegen/stub_options.h",
     "include/grpc++/impl/codegen/sync.h",
@@ -2041,6 +2056,7 @@
     "src/core/lib/support/log_linux.c",
     "src/core/lib/support/log_posix.c",
     "src/core/lib/support/log_windows.c",
+    "src/core/lib/support/mpscq.c",
     "src/core/lib/support/murmur_hash.c",
     "src/core/lib/support/percent_encoding.c",
     "src/core/lib/support/slice.c",
@@ -2112,6 +2128,7 @@
     "src/core/lib/support/backoff.h",
     "src/core/lib/support/block_annotate.h",
     "src/core/lib/support/env.h",
+    "src/core/lib/support/mpscq.h",
     "src/core/lib/support/murmur_hash.h",
     "src/core/lib/support/percent_encoding.h",
     "src/core/lib/support/stack_lockfree.h",
@@ -2150,6 +2167,7 @@
     "src/core/lib/http/httpcli.c",
     "src/core/lib/http/parser.c",
     "src/core/lib/iomgr/closure.c",
+    "src/core/lib/iomgr/combiner.c",
     "src/core/lib/iomgr/endpoint.c",
     "src/core/lib/iomgr/endpoint_pair_posix.c",
     "src/core/lib/iomgr/endpoint_pair_windows.c",
@@ -2365,6 +2383,7 @@
     "src/core/lib/http/httpcli.h",
     "src/core/lib/http/parser.h",
     "src/core/lib/iomgr/closure.h",
+    "src/core/lib/iomgr/combiner.h",
     "src/core/lib/iomgr/endpoint.h",
     "src/core/lib/iomgr/endpoint_pair.h",
     "src/core/lib/iomgr/error.h",
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 2b24c9a..6270365 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -191,6 +191,7 @@
   src/core/lib/support/log_linux.c
   src/core/lib/support/log_posix.c
   src/core/lib/support/log_windows.c
+  src/core/lib/support/mpscq.c
   src/core/lib/support/murmur_hash.c
   src/core/lib/support/percent_encoding.c
   src/core/lib/support/slice.c
@@ -304,6 +305,7 @@
   src/core/lib/http/httpcli.c
   src/core/lib/http/parser.c
   src/core/lib/iomgr/closure.c
+  src/core/lib/iomgr/combiner.c
   src/core/lib/iomgr/endpoint.c
   src/core/lib/iomgr/endpoint_pair_posix.c
   src/core/lib/iomgr/endpoint_pair_windows.c
@@ -558,6 +560,7 @@
   src/core/lib/http/httpcli.c
   src/core/lib/http/parser.c
   src/core/lib/iomgr/closure.c
+  src/core/lib/iomgr/combiner.c
   src/core/lib/iomgr/endpoint.c
   src/core/lib/iomgr/endpoint_pair_posix.c
   src/core/lib/iomgr/endpoint_pair_windows.c
@@ -785,6 +788,7 @@
   src/core/lib/http/httpcli.c
   src/core/lib/http/parser.c
   src/core/lib/iomgr/closure.c
+  src/core/lib/iomgr/combiner.c
   src/core/lib/iomgr/endpoint.c
   src/core/lib/iomgr/endpoint_pair_posix.c
   src/core/lib/iomgr/endpoint_pair_windows.c
@@ -1038,6 +1042,7 @@
   src/core/lib/http/httpcli.c
   src/core/lib/http/parser.c
   src/core/lib/iomgr/closure.c
+  src/core/lib/iomgr/combiner.c
   src/core/lib/iomgr/endpoint.c
   src/core/lib/iomgr/endpoint_pair_posix.c
   src/core/lib/iomgr/endpoint_pair_windows.c
@@ -1227,6 +1232,7 @@
   include/grpc++/impl/codegen/service_type.h
   include/grpc++/impl/codegen/status.h
   include/grpc++/impl/codegen/status_code_enum.h
+  include/grpc++/impl/codegen/status_helper.h
   include/grpc++/impl/codegen/string_ref.h
   include/grpc++/impl/codegen/stub_options.h
   include/grpc++/impl/codegen/sync.h
@@ -1300,6 +1306,7 @@
   include/grpc++/impl/codegen/service_type.h
   include/grpc++/impl/codegen/status.h
   include/grpc++/impl/codegen/status_code_enum.h
+  include/grpc++/impl/codegen/status_helper.h
   include/grpc++/impl/codegen/string_ref.h
   include/grpc++/impl/codegen/stub_options.h
   include/grpc++/impl/codegen/sync.h
@@ -1387,6 +1394,7 @@
   src/core/lib/http/httpcli.c
   src/core/lib/http/parser.c
   src/core/lib/iomgr/closure.c
+  src/core/lib/iomgr/combiner.c
   src/core/lib/iomgr/endpoint.c
   src/core/lib/iomgr/endpoint_pair_posix.c
   src/core/lib/iomgr/endpoint_pair_windows.c
@@ -1575,6 +1583,7 @@
   include/grpc++/impl/codegen/service_type.h
   include/grpc++/impl/codegen/status.h
   include/grpc++/impl/codegen/status_code_enum.h
+  include/grpc++/impl/codegen/status_helper.h
   include/grpc++/impl/codegen/string_ref.h
   include/grpc++/impl/codegen/stub_options.h
   include/grpc++/impl/codegen/sync.h
diff --git a/Makefile b/Makefile
index af4d4f4..98266f6 100644
--- a/Makefile
+++ b/Makefile
@@ -915,6 +915,7 @@
 chttp2_stream_map_test: $(BINDIR)/$(CONFIG)/chttp2_stream_map_test
 chttp2_varint_test: $(BINDIR)/$(CONFIG)/chttp2_varint_test
 client_fuzzer: $(BINDIR)/$(CONFIG)/client_fuzzer
+combiner_test: $(BINDIR)/$(CONFIG)/combiner_test
 compression_test: $(BINDIR)/$(CONFIG)/compression_test
 concurrent_connectivity_test: $(BINDIR)/$(CONFIG)/concurrent_connectivity_test
 dns_resolver_connectivity_test: $(BINDIR)/$(CONFIG)/dns_resolver_connectivity_test
@@ -940,6 +941,7 @@
 gpr_histogram_test: $(BINDIR)/$(CONFIG)/gpr_histogram_test
 gpr_host_port_test: $(BINDIR)/$(CONFIG)/gpr_host_port_test
 gpr_log_test: $(BINDIR)/$(CONFIG)/gpr_log_test
+gpr_mpscq_test: $(BINDIR)/$(CONFIG)/gpr_mpscq_test
 gpr_percent_encoding_test: $(BINDIR)/$(CONFIG)/gpr_percent_encoding_test
 gpr_slice_buffer_test: $(BINDIR)/$(CONFIG)/gpr_slice_buffer_test
 gpr_slice_test: $(BINDIR)/$(CONFIG)/gpr_slice_test
@@ -1240,6 +1242,7 @@
   $(BINDIR)/$(CONFIG)/chttp2_status_conversion_test \
   $(BINDIR)/$(CONFIG)/chttp2_stream_map_test \
   $(BINDIR)/$(CONFIG)/chttp2_varint_test \
+  $(BINDIR)/$(CONFIG)/combiner_test \
   $(BINDIR)/$(CONFIG)/compression_test \
   $(BINDIR)/$(CONFIG)/concurrent_connectivity_test \
   $(BINDIR)/$(CONFIG)/dns_resolver_connectivity_test \
@@ -1262,6 +1265,7 @@
   $(BINDIR)/$(CONFIG)/gpr_histogram_test \
   $(BINDIR)/$(CONFIG)/gpr_host_port_test \
   $(BINDIR)/$(CONFIG)/gpr_log_test \
+  $(BINDIR)/$(CONFIG)/gpr_mpscq_test \
   $(BINDIR)/$(CONFIG)/gpr_percent_encoding_test \
   $(BINDIR)/$(CONFIG)/gpr_slice_buffer_test \
   $(BINDIR)/$(CONFIG)/gpr_slice_test \
@@ -1557,6 +1561,8 @@
 	$(Q) $(BINDIR)/$(CONFIG)/chttp2_stream_map_test || ( echo test chttp2_stream_map_test failed ; exit 1 )
 	$(E) "[RUN]     Testing chttp2_varint_test"
 	$(Q) $(BINDIR)/$(CONFIG)/chttp2_varint_test || ( echo test chttp2_varint_test failed ; exit 1 )
+	$(E) "[RUN]     Testing combiner_test"
+	$(Q) $(BINDIR)/$(CONFIG)/combiner_test || ( echo test combiner_test failed ; exit 1 )
 	$(E) "[RUN]     Testing compression_test"
 	$(Q) $(BINDIR)/$(CONFIG)/compression_test || ( echo test compression_test failed ; exit 1 )
 	$(E) "[RUN]     Testing concurrent_connectivity_test"
@@ -1597,6 +1603,8 @@
 	$(Q) $(BINDIR)/$(CONFIG)/gpr_host_port_test || ( echo test gpr_host_port_test failed ; exit 1 )
 	$(E) "[RUN]     Testing gpr_log_test"
 	$(Q) $(BINDIR)/$(CONFIG)/gpr_log_test || ( echo test gpr_log_test failed ; exit 1 )
+	$(E) "[RUN]     Testing gpr_mpscq_test"
+	$(Q) $(BINDIR)/$(CONFIG)/gpr_mpscq_test || ( echo test gpr_mpscq_test failed ; exit 1 )
 	$(E) "[RUN]     Testing gpr_percent_encoding_test"
 	$(Q) $(BINDIR)/$(CONFIG)/gpr_percent_encoding_test || ( echo test gpr_percent_encoding_test failed ; exit 1 )
 	$(E) "[RUN]     Testing gpr_slice_buffer_test"
@@ -2378,6 +2386,7 @@
     src/core/lib/support/log_linux.c \
     src/core/lib/support/log_posix.c \
     src/core/lib/support/log_windows.c \
+    src/core/lib/support/mpscq.c \
     src/core/lib/support/murmur_hash.c \
     src/core/lib/support/percent_encoding.c \
     src/core/lib/support/slice.c \
@@ -2525,6 +2534,7 @@
     src/core/lib/http/httpcli.c \
     src/core/lib/http/parser.c \
     src/core/lib/iomgr/closure.c \
+    src/core/lib/iomgr/combiner.c \
     src/core/lib/iomgr/endpoint.c \
     src/core/lib/iomgr/endpoint_pair_posix.c \
     src/core/lib/iomgr/endpoint_pair_windows.c \
@@ -2797,6 +2807,7 @@
     src/core/lib/http/httpcli.c \
     src/core/lib/http/parser.c \
     src/core/lib/iomgr/closure.c \
+    src/core/lib/iomgr/combiner.c \
     src/core/lib/iomgr/endpoint.c \
     src/core/lib/iomgr/endpoint_pair_posix.c \
     src/core/lib/iomgr/endpoint_pair_windows.c \
@@ -3058,6 +3069,7 @@
     src/core/lib/http/httpcli.c \
     src/core/lib/http/parser.c \
     src/core/lib/iomgr/closure.c \
+    src/core/lib/iomgr/combiner.c \
     src/core/lib/iomgr/endpoint.c \
     src/core/lib/iomgr/endpoint_pair_posix.c \
     src/core/lib/iomgr/endpoint_pair_windows.c \
@@ -3247,6 +3259,7 @@
     src/core/lib/http/httpcli.c \
     src/core/lib/http/parser.c \
     src/core/lib/iomgr/closure.c \
+    src/core/lib/iomgr/combiner.c \
     src/core/lib/iomgr/endpoint.c \
     src/core/lib/iomgr/endpoint_pair_posix.c \
     src/core/lib/iomgr/endpoint_pair_windows.c \
@@ -3583,6 +3596,7 @@
     src/core/lib/http/httpcli.c \
     src/core/lib/http/parser.c \
     src/core/lib/iomgr/closure.c \
+    src/core/lib/iomgr/combiner.c \
     src/core/lib/iomgr/endpoint.c \
     src/core/lib/iomgr/endpoint_pair_posix.c \
     src/core/lib/iomgr/endpoint_pair_windows.c \
@@ -3754,6 +3768,7 @@
     include/grpc++/impl/codegen/service_type.h \
     include/grpc++/impl/codegen/status.h \
     include/grpc++/impl/codegen/status_code_enum.h \
+    include/grpc++/impl/codegen/status_helper.h \
     include/grpc++/impl/codegen/string_ref.h \
     include/grpc++/impl/codegen/stub_options.h \
     include/grpc++/impl/codegen/sync.h \
@@ -3859,6 +3874,7 @@
     include/grpc++/impl/codegen/service_type.h \
     include/grpc++/impl/codegen/status.h \
     include/grpc++/impl/codegen/status_code_enum.h \
+    include/grpc++/impl/codegen/status_helper.h \
     include/grpc++/impl/codegen/string_ref.h \
     include/grpc++/impl/codegen/stub_options.h \
     include/grpc++/impl/codegen/sync.h \
@@ -4082,6 +4098,7 @@
     include/grpc++/impl/codegen/service_type.h \
     include/grpc++/impl/codegen/status.h \
     include/grpc++/impl/codegen/status_code_enum.h \
+    include/grpc++/impl/codegen/status_helper.h \
     include/grpc++/impl/codegen/string_ref.h \
     include/grpc++/impl/codegen/stub_options.h \
     include/grpc++/impl/codegen/sync.h \
@@ -4206,6 +4223,7 @@
     src/core/lib/http/httpcli.c \
     src/core/lib/http/parser.c \
     src/core/lib/iomgr/closure.c \
+    src/core/lib/iomgr/combiner.c \
     src/core/lib/iomgr/endpoint.c \
     src/core/lib/iomgr/endpoint_pair_posix.c \
     src/core/lib/iomgr/endpoint_pair_windows.c \
@@ -4377,6 +4395,7 @@
     include/grpc++/impl/codegen/service_type.h \
     include/grpc++/impl/codegen/status.h \
     include/grpc++/impl/codegen/status_code_enum.h \
+    include/grpc++/impl/codegen/status_helper.h \
     include/grpc++/impl/codegen/string_ref.h \
     include/grpc++/impl/codegen/stub_options.h \
     include/grpc++/impl/codegen/sync.h \
@@ -7378,6 +7397,38 @@
 endif
 
 
+COMBINER_TEST_SRC = \
+    test/core/iomgr/combiner_test.c \
+
+COMBINER_TEST_OBJS = $(addprefix $(OBJDIR)/$(CONFIG)/, $(addsuffix .o, $(basename $(COMBINER_TEST_SRC))))
+ifeq ($(NO_SECURE),true)
+
+# You can't build secure targets if you don't have OpenSSL.
+
+$(BINDIR)/$(CONFIG)/combiner_test: openssl_dep_error
+
+else
+
+
+
+$(BINDIR)/$(CONFIG)/combiner_test: $(COMBINER_TEST_OBJS) $(LIBDIR)/$(CONFIG)/libgrpc_test_util.a $(LIBDIR)/$(CONFIG)/libgrpc.a $(LIBDIR)/$(CONFIG)/libgpr_test_util.a $(LIBDIR)/$(CONFIG)/libgpr.a
+	$(E) "[LD]      Linking $@"
+	$(Q) mkdir -p `dirname $@`
+	$(Q) $(LD) $(LDFLAGS) $(COMBINER_TEST_OBJS) $(LIBDIR)/$(CONFIG)/libgrpc_test_util.a $(LIBDIR)/$(CONFIG)/libgrpc.a $(LIBDIR)/$(CONFIG)/libgpr_test_util.a $(LIBDIR)/$(CONFIG)/libgpr.a $(LDLIBS) $(LDLIBS_SECURE) -o $(BINDIR)/$(CONFIG)/combiner_test
+
+endif
+
+$(OBJDIR)/$(CONFIG)/test/core/iomgr/combiner_test.o:  $(LIBDIR)/$(CONFIG)/libgrpc_test_util.a $(LIBDIR)/$(CONFIG)/libgrpc.a $(LIBDIR)/$(CONFIG)/libgpr_test_util.a $(LIBDIR)/$(CONFIG)/libgpr.a
+
+deps_combiner_test: $(COMBINER_TEST_OBJS:.o=.dep)
+
+ifneq ($(NO_SECURE),true)
+ifneq ($(NO_DEPS),true)
+-include $(COMBINER_TEST_OBJS:.o=.dep)
+endif
+endif
+
+
 COMPRESSION_TEST_SRC = \
     test/core/compression/compression_test.c \
 
@@ -8178,6 +8229,38 @@
 endif
 
 
+GPR_MPSCQ_TEST_SRC = \
+    test/core/support/mpscq_test.c \
+
+GPR_MPSCQ_TEST_OBJS = $(addprefix $(OBJDIR)/$(CONFIG)/, $(addsuffix .o, $(basename $(GPR_MPSCQ_TEST_SRC))))
+ifeq ($(NO_SECURE),true)
+
+# You can't build secure targets if you don't have OpenSSL.
+
+$(BINDIR)/$(CONFIG)/gpr_mpscq_test: openssl_dep_error
+
+else
+
+
+
+$(BINDIR)/$(CONFIG)/gpr_mpscq_test: $(GPR_MPSCQ_TEST_OBJS) $(LIBDIR)/$(CONFIG)/libgpr_test_util.a $(LIBDIR)/$(CONFIG)/libgpr.a
+	$(E) "[LD]      Linking $@"
+	$(Q) mkdir -p `dirname $@`
+	$(Q) $(LD) $(LDFLAGS) $(GPR_MPSCQ_TEST_OBJS) $(LIBDIR)/$(CONFIG)/libgpr_test_util.a $(LIBDIR)/$(CONFIG)/libgpr.a $(LDLIBS) $(LDLIBS_SECURE) -o $(BINDIR)/$(CONFIG)/gpr_mpscq_test
+
+endif
+
+$(OBJDIR)/$(CONFIG)/test/core/support/mpscq_test.o:  $(LIBDIR)/$(CONFIG)/libgpr_test_util.a $(LIBDIR)/$(CONFIG)/libgpr.a
+
+deps_gpr_mpscq_test: $(GPR_MPSCQ_TEST_OBJS:.o=.dep)
+
+ifneq ($(NO_SECURE),true)
+ifneq ($(NO_DEPS),true)
+-include $(GPR_MPSCQ_TEST_OBJS:.o=.dep)
+endif
+endif
+
+
 GPR_PERCENT_ENCODING_TEST_SRC = \
     test/core/support/percent_encoding_test.c \
 
diff --git a/binding.gyp b/binding.gyp
index 7cc8a58..b4f182c 100644
--- a/binding.gyp
+++ b/binding.gyp
@@ -515,6 +515,7 @@
         'src/core/lib/support/log_linux.c',
         'src/core/lib/support/log_posix.c',
         'src/core/lib/support/log_windows.c',
+        'src/core/lib/support/mpscq.c',
         'src/core/lib/support/murmur_hash.c',
         'src/core/lib/support/percent_encoding.c',
         'src/core/lib/support/slice.c',
@@ -579,6 +580,7 @@
         'src/core/lib/http/httpcli.c',
         'src/core/lib/http/parser.c',
         'src/core/lib/iomgr/closure.c',
+        'src/core/lib/iomgr/combiner.c',
         'src/core/lib/iomgr/endpoint.c',
         'src/core/lib/iomgr/endpoint_pair_posix.c',
         'src/core/lib/iomgr/endpoint_pair_windows.c',
diff --git a/build.yaml b/build.yaml
index cd115c7..65cdea7 100644
--- a/build.yaml
+++ b/build.yaml
@@ -82,6 +82,7 @@
   - src/core/lib/support/backoff.h
   - src/core/lib/support/block_annotate.h
   - src/core/lib/support/env.h
+  - src/core/lib/support/mpscq.h
   - src/core/lib/support/murmur_hash.h
   - src/core/lib/support/percent_encoding.h
   - src/core/lib/support/stack_lockfree.h
@@ -111,6 +112,7 @@
   - src/core/lib/support/log_linux.c
   - src/core/lib/support/log_posix.c
   - src/core/lib/support/log_windows.c
+  - src/core/lib/support/mpscq.c
   - src/core/lib/support/murmur_hash.c
   - src/core/lib/support/percent_encoding.c
   - src/core/lib/support/slice.c
@@ -178,6 +180,7 @@
   - src/core/lib/http/httpcli.h
   - src/core/lib/http/parser.h
   - src/core/lib/iomgr/closure.h
+  - src/core/lib/iomgr/combiner.h
   - src/core/lib/iomgr/endpoint.h
   - src/core/lib/iomgr/endpoint_pair.h
   - src/core/lib/iomgr/error.h
@@ -258,6 +261,7 @@
   - src/core/lib/http/httpcli.c
   - src/core/lib/http/parser.c
   - src/core/lib/iomgr/closure.c
+  - src/core/lib/iomgr/combiner.c
   - src/core/lib/iomgr/endpoint.c
   - src/core/lib/iomgr/endpoint_pair_posix.c
   - src/core/lib/iomgr/endpoint_pair_windows.c
@@ -754,6 +758,7 @@
   - include/grpc++/impl/codegen/service_type.h
   - include/grpc++/impl/codegen/status.h
   - include/grpc++/impl/codegen/status_code_enum.h
+  - include/grpc++/impl/codegen/status_helper.h
   - include/grpc++/impl/codegen/string_ref.h
   - include/grpc++/impl/codegen/stub_options.h
   - include/grpc++/impl/codegen/sync.h
@@ -1404,6 +1409,17 @@
   - test/core/end2end/fuzzers/client_fuzzer_corpus
   dict: test/core/end2end/fuzzers/hpack.dictionary
   maxlen: 2048
+- name: combiner_test
+  cpu_cost: 30
+  build: test
+  language: c
+  src:
+  - test/core/iomgr/combiner_test.c
+  deps:
+  - grpc_test_util
+  - grpc
+  - gpr_test_util
+  - gpr
 - name: compression_test
   build: test
   language: c
@@ -1661,6 +1677,15 @@
   deps:
   - gpr_test_util
   - gpr
+- name: gpr_mpscq_test
+  cpu_cost: 30
+  build: test
+  language: c
+  src:
+  - test/core/support/mpscq_test.c
+  deps:
+  - gpr_test_util
+  - gpr
 - name: gpr_percent_encoding_test
   build: test
   language: c
diff --git a/config.m4 b/config.m4
index 5384585..5947306 100644
--- a/config.m4
+++ b/config.m4
@@ -56,6 +56,7 @@
     src/core/lib/support/log_linux.c \
     src/core/lib/support/log_posix.c \
     src/core/lib/support/log_windows.c \
+    src/core/lib/support/mpscq.c \
     src/core/lib/support/murmur_hash.c \
     src/core/lib/support/percent_encoding.c \
     src/core/lib/support/slice.c \
@@ -98,6 +99,7 @@
     src/core/lib/http/httpcli.c \
     src/core/lib/http/parser.c \
     src/core/lib/iomgr/closure.c \
+    src/core/lib/iomgr/combiner.c \
     src/core/lib/iomgr/endpoint.c \
     src/core/lib/iomgr/endpoint_pair_posix.c \
     src/core/lib/iomgr/endpoint_pair_windows.c \
diff --git a/doc/http-grpc-status-mapping.md b/doc/http-grpc-status-mapping.md
new file mode 100644
index 0000000..928fe54
--- /dev/null
+++ b/doc/http-grpc-status-mapping.md
@@ -0,0 +1,30 @@
+# HTTP to gRPC Status Code Mapping
+
+Since intermediaries are a common part of HTTP infrastructure some responses to
+gRPC requests may be received that do not include the grpc-status header. In
+some cases mapping error codes from an intermediary allows the gRPC client to
+behave more appropriately to the error situation without overloading the
+semantics of either error code.
+
+This table is to be used _only_ for clients that received a response that did
+not include grpc-status. If grpc-status was provided, it _must_ be used. Servers
+_must not_ use this table to determine an HTTP status code to use; the mappings
+are neither symmetric nor 1-to-1.
+
+| HTTP Status Code           | gRPC Status Code   |
+|----------------------------|--------------------|
+| 400 Bad Request            | INTERNAL           |
+| 401 Unauthorized           | UNAUTHENTICATED    |
+| 403 Forbidden              | PERMISSION\_DENIED |
+| 404 Not Found              | UNIMPLEMENTED      |
+| 429 Too Many Requests      | UNAVAILABLE        |
+| 502 Bad Gateway            | UNAVAILABLE        |
+| 503 Service Unavailable    | UNAVAILABLE        |
+| 504 Gateway Timeout        | UNAVAILABLE        |
+| _All other codes_          | UNKNOWN            |
+
+Technically, 1xx should have the entire header skipped and a subsequent header
+be read. See RFC 7540 §8.1.
+
+200 is UNKNOWN because there should be a grpc-status in case of truly OK
+response.
diff --git a/doc/server_reflection_tutorial.md b/doc/server_reflection_tutorial.md
new file mode 100644
index 0000000..ecb1767
--- /dev/null
+++ b/doc/server_reflection_tutorial.md
@@ -0,0 +1,192 @@
+# gRPC Server Reflection Tutorial
+
+gRPC Server Reflection provides information about publicly-accessible gRPC
+services on a server, and assists clients at runtime to construct RPC
+requests and responses without precompiled service information. It is used by
+gRPC CLI, which can be used to introspect server protos and send/receive test
+RPCs.
+
+## Enable Server Reflection
+
+### Enable server reflection in C++ servers
+
+C++ Server Reflection is an add-on library, `libgrpc++_reflction`. To enable C++
+server reflection, you can link this library to your server binary.
+
+Some platforms (e.g. Ubuntu 11.10 onwards) only link in libraries that directly
+contain symbols used by the application. On these platforms, LD flag
+`--no-as-needed` is needed for for dynamic linking and `--whole-archive` is
+needed for for static linking.
+
+This [Makefile](../examples/cpp/helloworld/Makefile#L37#L45) demonstrates
+enabling c++ server reflection on Linux and MacOS.
+
+## Test services using Server Reflection
+
+After enabling Server Reflection in a server application, you can use gRPC CLI
+to test its services.
+
+Instructions on how to use gRPC CLI can be found at
+[command_line_tool.md](command_line_tool.md), or using `grpc_cli help` command.
+
+Here we use `examples/cpp/helloworld` as an example to show the use of gRPC
+Server Reflection and gRPC CLI. First, we need to build gRPC CLI and setup an
+example server with Server Reflection enabled.
+
+- Setup an example server
+
+  Server Reflection has already been enabled in the
+  [Makefile](../examples/cpp/helloworld/Makefile) of the helloworld example. We
+  can simply make it and run the greeter_server.
+
+  ```sh
+  $ make -C examples/cpp/helloworld
+  $ examples/cpp/helloworld/greeter_server &
+  ```
+
+- Build gRPC CLI
+
+  ```sh
+  make grpc_cli
+  cd bins/opt
+  ```
+
+  gRPC CLI binary `grpc_cli` can be found at `bins/opt/` folder. This tool is
+  still new and does not have a `make install` target yet.
+
+### List services
+
+`grpc_cli ls` command lists services and methods exposed at a given port
+
+- List all the services exposed at a given port
+
+  ```sh
+  $ grpc_cli ls localhost:50051
+  ```
+
+  output:
+  ```sh
+  helloworld.Greeter
+  grpc.reflection.v1alpha.ServerReflection
+  ```
+
+- List one service with details
+
+  `grpc_cli ls` command inspects a service given its full name (in the format of
+  \<package\>.\<service\>). It can print information with a long listing format
+  when `-l` flag is set. This flag can be used to get more details about a
+  service.
+
+  ```sh
+  $ grpc_cli ls localhost:50051 helloworld.Greeter -l
+  ```
+
+  output:
+  ```sh
+  filename: helloworld.proto
+  package: helloworld;
+  service Greeter {
+    rpc SayHello(helloworld.HelloRequest) returns (helloworld.HelloReply) {}
+  }
+
+  ```
+
+### List methods
+
+- List one method with details
+
+  `grpc_cli ls` command also inspects a method given its full name (in the
+  format of \<package\>.\<service\>.\<method\>).
+
+  ```sh
+  $ grpc_cli ls localhost:50051 helloworld.Greeter.SayHello -l
+  ```
+
+  output:
+  ```sh
+    rpc SayHello(helloworld.HelloRequest) returns (helloworld.HelloReply) {}
+  ```
+
+### Inspect message types
+
+We can use`grpc_cli type` command to inspect request/response types given the
+full name of the type (in the format of \<package\>.\<type\>).
+
+- Get information about the request type
+
+  ```sh
+  $ grpc_cli type localhost:50051 helloworld.HelloRequest
+  ```
+
+  output:
+  ```sh
+  message HelloRequest {
+    optional string name = 1;
+  }
+  ```
+
+### Call a remote method
+
+We can send RPCs to a server and get responses using `grpc_cli call` command.
+
+- Call a unary method
+
+  ```sh
+  $ grpc_cli call localhost:50051 SayHello "name: 'gRPC CLI'"
+  ```
+
+  output:
+  ```sh
+  message: "Hello gRPC CLI"
+  ```
+
+## Use Server Reflection in a C++ client
+
+Server Reflection can be used by clients to get information about gRPC services
+at runtime. We've provided a descriptor database called
+[grpc::ProtoReflectionDescriptorDatabase](../test/cpp/util/proto_reflection_descriptor_database.h)
+which implements the
+[google::protobuf::DescriptorDatabase](https://developers.google.com/protocol-buffers/docs/reference/cpp/google.protobuf.descriptor_database#DescriptorDatabase)
+interface. It manages the communication between clients and reflection services
+and the storage of received information. Clients can use it as using a local
+descriptor database.
+
+- To use Server Reflection with grpc::ProtoReflectionDescriptorDatabase, first
+  initialize an instance with a grpc::Channel.
+
+  ```c++
+  std::shared_ptr<grpc::Channel> channel =
+      grpc::CreateChannel(server_address, server_cred);
+  grpc::ProtoReflectionDescriptorDatabase reflection_db(channel);
+  ```
+
+- Then use this instance to feed a
+  [google::protobuf::DescriptorPool](https://developers.google.com/protocol-buffers/docs/reference/cpp/google.protobuf.descriptor#DescriptorPool).
+
+  ```c++
+  google::protobuf::DescriptorPool desc_pool(&reflection_db);
+  ```
+
+- Example usage of this descriptor pool
+
+  * Get Service/method descriptors.
+
+    ```c++
+    const google::protobuf::ServiceDescriptor* service_desc =
+        desc_pool->FindServiceByName("helloworld.Greeter");
+    const google::protobuf::MethodDescriptor* method_desc =
+        desc_pool->FindMethodByName("helloworld.Greeter.SayHello");
+    ```
+
+  * Get message type descriptors.
+
+    ```c++
+    const google::protobuf::Descriptor* request_desc =
+        desc_pool->FindMessageTypeByName("helloworld.HelloRequest");
+    ```
+
+  * Feed [google::protobuf::DynamicMessageFactory](https://developers.google.com/protocol-buffers/docs/reference/cpp/google.protobuf.dynamic_message#DynamicMessageFactory).
+
+    ```c++
+    google::protobuf::DynamicMessageFactory(&desc_pool);
+    ```
diff --git a/etc/README.md b/etc/README.md
new file mode 100644
index 0000000..87af44f
--- /dev/null
+++ b/etc/README.md
@@ -0,0 +1,4 @@
+The roots.pem file is periodically generated from:
+https://hg.mozilla.org/mozilla-central/raw-file/tip/security/nss/lib/ckfw/builtins/certdata.txt
+using
+https://github.com/agl/extract-nss-root-certs
diff --git a/etc/roots.pem b/etc/roots.pem
index e6df88e..d376e58 100644
--- a/etc/roots.pem
+++ b/etc/roots.pem
@@ -5387,3 +5387,42 @@
 j9uEwov1NcoG3GRvaBbhj5G5AjEA2Euly8LQCGzpGPta3U1fJAuwACEl74+nBCZx
 4nxp5V2a+EEfOzmTk51V6s2N8fvB
 -----END CERTIFICATE-----
+
+# Issuer: CN=ISRG Root X1 O=Internet Security Research Group
+# Subject: CN=ISRG Root X1 O=Internet Security Research Group
+# Label: "ISRG Root X1"
+# Serial: 172886928669790476064670243504169061120
+# MD5 Fingerprint: 0c:d2:f9:e0:da:17:73:e9:ed:86:4d:a5:e3:70:e7:4e
+# SHA1 Fingerprint: ca:bd:2a:79:a1:07:6a:31:f2:1d:25:36:35:cb:03:9d:43:29:a5:e8
+# SHA256 Fingerprint: 96:bc:ec:06:26:49:76:f3:74:60:77:9a:cf:28:c5:a7:cf:e8:a3:c0:aa:e1:1a:8f:fc:ee:05:c0:bd:df:08:c6
+-----BEGIN CERTIFICATE-----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=
+-----END CERTIFICATE-----
diff --git a/examples/cpp/helloworld/greeter_async_client.cc b/examples/cpp/helloworld/greeter_async_client.cc
index 33de59f..595baae 100644
--- a/examples/cpp/helloworld/greeter_async_client.cc
+++ b/examples/cpp/helloworld/greeter_async_client.cc
@@ -36,6 +36,7 @@
 #include <string>
 
 #include <grpc++/grpc++.h>
+#include <grpc/support/log.h>
 
 #include "helloworld.grpc.pb.h"
 
diff --git a/examples/cpp/helloworld/greeter_async_client2.cc b/examples/cpp/helloworld/greeter_async_client2.cc
index 0902376..fe0a213 100644
--- a/examples/cpp/helloworld/greeter_async_client2.cc
+++ b/examples/cpp/helloworld/greeter_async_client2.cc
@@ -36,6 +36,7 @@
 #include <string>
 
 #include <grpc++/grpc++.h>
+#include <grpc/support/log.h>
 #include <thread>
 
 #include "helloworld.grpc.pb.h"
diff --git a/examples/cpp/helloworld/greeter_async_server.cc b/examples/cpp/helloworld/greeter_async_server.cc
index ead4418..bd14b0e 100644
--- a/examples/cpp/helloworld/greeter_async_server.cc
+++ b/examples/cpp/helloworld/greeter_async_server.cc
@@ -37,6 +37,7 @@
 #include <thread>
 
 #include <grpc++/grpc++.h>
+#include <grpc/support/log.h>
 
 #include "helloworld.grpc.pb.h"
 
diff --git a/gRPC-Core.podspec b/gRPC-Core.podspec
index 1fd96bb..c740787 100644
--- a/gRPC-Core.podspec
+++ b/gRPC-Core.podspec
@@ -193,6 +193,7 @@
                       'src/core/lib/support/backoff.h',
                       'src/core/lib/support/block_annotate.h',
                       'src/core/lib/support/env.h',
+                      'src/core/lib/support/mpscq.h',
                       'src/core/lib/support/murmur_hash.h',
                       'src/core/lib/support/percent_encoding.h',
                       'src/core/lib/support/stack_lockfree.h',
@@ -221,6 +222,7 @@
                       'src/core/lib/support/log_linux.c',
                       'src/core/lib/support/log_posix.c',
                       'src/core/lib/support/log_windows.c',
+                      'src/core/lib/support/mpscq.c',
                       'src/core/lib/support/murmur_hash.c',
                       'src/core/lib/support/percent_encoding.c',
                       'src/core/lib/support/slice.c',
@@ -263,6 +265,7 @@
                       'src/core/lib/http/httpcli.h',
                       'src/core/lib/http/parser.h',
                       'src/core/lib/iomgr/closure.h',
+                      'src/core/lib/iomgr/combiner.h',
                       'src/core/lib/iomgr/endpoint.h',
                       'src/core/lib/iomgr/endpoint_pair.h',
                       'src/core/lib/iomgr/error.h',
@@ -422,6 +425,7 @@
                       'src/core/lib/http/httpcli.c',
                       'src/core/lib/http/parser.c',
                       'src/core/lib/iomgr/closure.c',
+                      'src/core/lib/iomgr/combiner.c',
                       'src/core/lib/iomgr/endpoint.c',
                       'src/core/lib/iomgr/endpoint_pair_posix.c',
                       'src/core/lib/iomgr/endpoint_pair_windows.c',
@@ -601,6 +605,7 @@
                               'src/core/lib/support/backoff.h',
                               'src/core/lib/support/block_annotate.h',
                               'src/core/lib/support/env.h',
+                              'src/core/lib/support/mpscq.h',
                               'src/core/lib/support/murmur_hash.h',
                               'src/core/lib/support/percent_encoding.h',
                               'src/core/lib/support/stack_lockfree.h',
@@ -625,6 +630,7 @@
                               'src/core/lib/http/httpcli.h',
                               'src/core/lib/http/parser.h',
                               'src/core/lib/iomgr/closure.h',
+                              'src/core/lib/iomgr/combiner.h',
                               'src/core/lib/iomgr/endpoint.h',
                               'src/core/lib/iomgr/endpoint_pair.h',
                               'src/core/lib/iomgr/error.h',
diff --git a/grpc.gemspec b/grpc.gemspec
index 7f608e0..5d85108 100755
--- a/grpc.gemspec
+++ b/grpc.gemspec
@@ -87,6 +87,7 @@
   s.files += %w( src/core/lib/support/backoff.h )
   s.files += %w( src/core/lib/support/block_annotate.h )
   s.files += %w( src/core/lib/support/env.h )
+  s.files += %w( src/core/lib/support/mpscq.h )
   s.files += %w( src/core/lib/support/murmur_hash.h )
   s.files += %w( src/core/lib/support/percent_encoding.h )
   s.files += %w( src/core/lib/support/stack_lockfree.h )
@@ -115,6 +116,7 @@
   s.files += %w( src/core/lib/support/log_linux.c )
   s.files += %w( src/core/lib/support/log_posix.c )
   s.files += %w( src/core/lib/support/log_windows.c )
+  s.files += %w( src/core/lib/support/mpscq.c )
   s.files += %w( src/core/lib/support/murmur_hash.c )
   s.files += %w( src/core/lib/support/percent_encoding.c )
   s.files += %w( src/core/lib/support/slice.c )
@@ -183,6 +185,7 @@
   s.files += %w( src/core/lib/http/httpcli.h )
   s.files += %w( src/core/lib/http/parser.h )
   s.files += %w( src/core/lib/iomgr/closure.h )
+  s.files += %w( src/core/lib/iomgr/combiner.h )
   s.files += %w( src/core/lib/iomgr/endpoint.h )
   s.files += %w( src/core/lib/iomgr/endpoint_pair.h )
   s.files += %w( src/core/lib/iomgr/error.h )
@@ -342,6 +345,7 @@
   s.files += %w( src/core/lib/http/httpcli.c )
   s.files += %w( src/core/lib/http/parser.c )
   s.files += %w( src/core/lib/iomgr/closure.c )
+  s.files += %w( src/core/lib/iomgr/combiner.c )
   s.files += %w( src/core/lib/iomgr/endpoint.c )
   s.files += %w( src/core/lib/iomgr/endpoint_pair_posix.c )
   s.files += %w( src/core/lib/iomgr/endpoint_pair_windows.c )
diff --git a/include/grpc++/impl/codegen/call.h b/include/grpc++/impl/codegen/call.h
index 4221357..2008728 100644
--- a/include/grpc++/impl/codegen/call.h
+++ b/include/grpc++/impl/codegen/call.h
@@ -46,6 +46,7 @@
 #include <grpc++/impl/codegen/core_codegen_interface.h>
 #include <grpc++/impl/codegen/serialization_traits.h>
 #include <grpc++/impl/codegen/status.h>
+#include <grpc++/impl/codegen/status_helper.h>
 #include <grpc++/impl/codegen/string_ref.h>
 
 #include <grpc/impl/codegen/compression_types.h>
@@ -433,7 +434,7 @@
     trailing_metadata_count_ = trailing_metadata.size();
     trailing_metadata_ = FillMetadataArray(trailing_metadata);
     send_status_available_ = true;
-    send_status_code_ = static_cast<grpc_status_code>(status.error_code());
+    send_status_code_ = static_cast<grpc_status_code>(GetCanonicalCode(status));
     send_status_details_ = status.error_message();
   }
 
diff --git a/include/grpc++/impl/codegen/status_helper.h b/include/grpc++/impl/codegen/status_helper.h
new file mode 100644
index 0000000..bfe45d9
--- /dev/null
+++ b/include/grpc++/impl/codegen/status_helper.h
@@ -0,0 +1,47 @@
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifndef GRPCXX_IMPL_CODEGEN_STATUS_HELPER_H
+#define GRPCXX_IMPL_CODEGEN_STATUS_HELPER_H
+
+#include <grpc++/impl/codegen/status.h>
+
+namespace grpc {
+
+inline StatusCode GetCanonicalCode(const Status& status) {
+  return status.error_code();
+}
+
+}  // namespace grpc
+
+#endif  // GRPCXX_IMPL_CODEGEN_STATUS_HELPER_H
diff --git a/include/grpc/impl/codegen/atm.h b/include/grpc/impl/codegen/atm.h
index 5589d5d..ae00fb0 100644
--- a/include/grpc/impl/codegen/atm.h
+++ b/include/grpc/impl/codegen/atm.h
@@ -75,6 +75,9 @@
    int gpr_atm_no_barrier_cas(gpr_atm *p, gpr_atm o, gpr_atm n);
    int gpr_atm_acq_cas(gpr_atm *p, gpr_atm o, gpr_atm n);
    int gpr_atm_rel_cas(gpr_atm *p, gpr_atm o, gpr_atm n);
+
+   // Atomically, set *p=n and return the old value of *p
+   gpr_atm gpr_atm_full_xchg(gpr_atm *p, gpr_atm n);
 */
 
 #include <grpc/impl/codegen/port_platform.h>
diff --git a/include/grpc/impl/codegen/atm_gcc_atomic.h b/include/grpc/impl/codegen/atm_gcc_atomic.h
index 8caf7ed..7d4ae98 100644
--- a/include/grpc/impl/codegen/atm_gcc_atomic.h
+++ b/include/grpc/impl/codegen/atm_gcc_atomic.h
@@ -69,4 +69,6 @@
                                      __ATOMIC_RELAXED);
 }
 
+#define gpr_atm_full_xchg(p, n) __atomic_exchange_n((p), (n), __ATOMIC_ACQ_REL)
+
 #endif /* GRPC_IMPL_CODEGEN_ATM_GCC_ATOMIC_H */
diff --git a/include/grpc/impl/codegen/atm_gcc_sync.h b/include/grpc/impl/codegen/atm_gcc_sync.h
index 915b09f..9aa2b43 100644
--- a/include/grpc/impl/codegen/atm_gcc_sync.h
+++ b/include/grpc/impl/codegen/atm_gcc_sync.h
@@ -84,4 +84,12 @@
 #define gpr_atm_acq_cas(p, o, n) (__sync_bool_compare_and_swap((p), (o), (n)))
 #define gpr_atm_rel_cas(p, o, n) gpr_atm_acq_cas((p), (o), (n))
 
+static __inline gpr_atm gpr_atm_full_xchg(gpr_atm *p, gpr_atm n) {
+  gpr_atm cur;
+  do {
+    cur = gpr_atm_acq_load(p);
+  } while (!gpr_atm_rel_cas(p, cur, n));
+  return cur;
+}
+
 #endif /* GRPC_IMPL_CODEGEN_ATM_GCC_SYNC_H */
diff --git a/include/grpc/impl/codegen/atm_windows.h b/include/grpc/impl/codegen/atm_windows.h
index d5fa8c0..0ab70b9 100644
--- a/include/grpc/impl/codegen/atm_windows.h
+++ b/include/grpc/impl/codegen/atm_windows.h
@@ -122,4 +122,8 @@
   return old;
 }
 
+static __inline gpr_atm gpr_atm_full_xchg(gpr_atm *p, gpr_atm n) {
+  return (gpr_atm)InterlockedExchangePointer((PVOID *)p, (PVOID)n);
+}
+
 #endif /* GRPC_IMPL_CODEGEN_ATM_WINDOWS_H */
diff --git a/package.xml b/package.xml
index 8262ef6..7432830 100644
--- a/package.xml
+++ b/package.xml
@@ -94,6 +94,7 @@
     <file baseinstalldir="/" name="src/core/lib/support/backoff.h" role="src" />
     <file baseinstalldir="/" name="src/core/lib/support/block_annotate.h" role="src" />
     <file baseinstalldir="/" name="src/core/lib/support/env.h" role="src" />
+    <file baseinstalldir="/" name="src/core/lib/support/mpscq.h" role="src" />
     <file baseinstalldir="/" name="src/core/lib/support/murmur_hash.h" role="src" />
     <file baseinstalldir="/" name="src/core/lib/support/percent_encoding.h" role="src" />
     <file baseinstalldir="/" name="src/core/lib/support/stack_lockfree.h" role="src" />
@@ -122,6 +123,7 @@
     <file baseinstalldir="/" name="src/core/lib/support/log_linux.c" role="src" />
     <file baseinstalldir="/" name="src/core/lib/support/log_posix.c" role="src" />
     <file baseinstalldir="/" name="src/core/lib/support/log_windows.c" role="src" />
+    <file baseinstalldir="/" name="src/core/lib/support/mpscq.c" role="src" />
     <file baseinstalldir="/" name="src/core/lib/support/murmur_hash.c" role="src" />
     <file baseinstalldir="/" name="src/core/lib/support/percent_encoding.c" role="src" />
     <file baseinstalldir="/" name="src/core/lib/support/slice.c" role="src" />
@@ -190,6 +192,7 @@
     <file baseinstalldir="/" name="src/core/lib/http/httpcli.h" role="src" />
     <file baseinstalldir="/" name="src/core/lib/http/parser.h" role="src" />
     <file baseinstalldir="/" name="src/core/lib/iomgr/closure.h" role="src" />
+    <file baseinstalldir="/" name="src/core/lib/iomgr/combiner.h" role="src" />
     <file baseinstalldir="/" name="src/core/lib/iomgr/endpoint.h" role="src" />
     <file baseinstalldir="/" name="src/core/lib/iomgr/endpoint_pair.h" role="src" />
     <file baseinstalldir="/" name="src/core/lib/iomgr/error.h" role="src" />
@@ -349,6 +352,7 @@
     <file baseinstalldir="/" name="src/core/lib/http/httpcli.c" role="src" />
     <file baseinstalldir="/" name="src/core/lib/http/parser.c" role="src" />
     <file baseinstalldir="/" name="src/core/lib/iomgr/closure.c" role="src" />
+    <file baseinstalldir="/" name="src/core/lib/iomgr/combiner.c" role="src" />
     <file baseinstalldir="/" name="src/core/lib/iomgr/endpoint.c" role="src" />
     <file baseinstalldir="/" name="src/core/lib/iomgr/endpoint_pair_posix.c" role="src" />
     <file baseinstalldir="/" name="src/core/lib/iomgr/endpoint_pair_windows.c" role="src" />
diff --git a/src/core/ext/client_config/client_channel.c b/src/core/ext/client_config/client_channel.c
index 61e0125..6b779ef 100644
--- a/src/core/ext/client_config/client_channel.c
+++ b/src/core/ext/client_config/client_channel.c
@@ -387,13 +387,15 @@
   grpc_connected_subchannel *connected_subchannel;
   grpc_polling_entity *pollent;
 
-  grpc_transport_stream_op *waiting_ops;
+  grpc_transport_stream_op **waiting_ops;
   size_t waiting_ops_count;
   size_t waiting_ops_capacity;
 
   grpc_closure next_step;
 
   grpc_call_stack *owning_call;
+
+  grpc_linked_mdelem lb_token_mdelem;
 } call_data;
 
 static void add_waiting_locked(call_data *calld, grpc_transport_stream_op *op) {
@@ -404,7 +406,7 @@
         gpr_realloc(calld->waiting_ops,
                     calld->waiting_ops_capacity * sizeof(*calld->waiting_ops));
   }
-  calld->waiting_ops[calld->waiting_ops_count++] = *op;
+  calld->waiting_ops[calld->waiting_ops_count++] = op;
   GPR_TIMER_END("add_waiting_locked", 0);
 }
 
@@ -413,14 +415,14 @@
   size_t i;
   for (i = 0; i < calld->waiting_ops_count; i++) {
     grpc_transport_stream_op_finish_with_failure(
-        exec_ctx, &calld->waiting_ops[i], GRPC_ERROR_REF(error));
+        exec_ctx, calld->waiting_ops[i], GRPC_ERROR_REF(error));
   }
   calld->waiting_ops_count = 0;
   GRPC_ERROR_UNREF(error);
 }
 
 typedef struct {
-  grpc_transport_stream_op *ops;
+  grpc_transport_stream_op **ops;
   size_t nops;
   grpc_subchannel_call *call;
 } retry_ops_args;
@@ -429,7 +431,7 @@
   retry_ops_args *a = args;
   size_t i;
   for (i = 0; i < a->nops; i++) {
-    grpc_subchannel_call_process_op(exec_ctx, a->call, &a->ops[i]);
+    grpc_subchannel_call_process_op(exec_ctx, a->call, a->ops[i]);
   }
   GRPC_SUBCHANNEL_CALL_UNREF(exec_ctx, a->call, "retry_ops");
   gpr_free(a->ops);
@@ -437,6 +439,10 @@
 }
 
 static void retry_waiting_locked(grpc_exec_ctx *exec_ctx, call_data *calld) {
+  if (calld->waiting_ops_count == 0) {
+    return;
+  }
+
   retry_ops_args *a = gpr_malloc(sizeof(*a));
   a->ops = calld->waiting_ops;
   a->nops = calld->waiting_ops_count;
@@ -566,9 +572,11 @@
     int r;
     GRPC_LB_POLICY_REF(lb_policy, "pick_subchannel");
     gpr_mu_unlock(&chand->mu);
-    r = grpc_lb_policy_pick(exec_ctx, lb_policy, calld->pollent,
-                            initial_metadata, initial_metadata_flags,
-                            connected_subchannel, on_ready);
+    const grpc_lb_policy_pick_args inputs = {calld->pollent, initial_metadata,
+                                             initial_metadata_flags,
+                                             &calld->lb_token_mdelem};
+    r = grpc_lb_policy_pick(exec_ctx, lb_policy, &inputs, connected_subchannel,
+                            NULL, on_ready);
     GRPC_LB_POLICY_UNREF(exec_ctx, lb_policy, "pick_subchannel");
     GPR_TIMER_END("pick_subchannel", 0);
     return r;
diff --git a/src/core/ext/client_config/lb_policy.c b/src/core/ext/client_config/lb_policy.c
index 8b980b2..903563e 100644
--- a/src/core/ext/client_config/lb_policy.c
+++ b/src/core/ext/client_config/lb_policy.c
@@ -100,13 +100,11 @@
 }
 
 int grpc_lb_policy_pick(grpc_exec_ctx *exec_ctx, grpc_lb_policy *policy,
-                        grpc_polling_entity *pollent,
-                        grpc_metadata_batch *initial_metadata,
-                        uint32_t initial_metadata_flags,
-                        grpc_connected_subchannel **target,
+                        const grpc_lb_policy_pick_args *pick_args,
+                        grpc_connected_subchannel **target, void **user_data,
                         grpc_closure *on_complete) {
-  return policy->vtable->pick(exec_ctx, policy, pollent, initial_metadata,
-                              initial_metadata_flags, target, on_complete);
+  return policy->vtable->pick(exec_ctx, policy, pick_args, target, user_data,
+                              on_complete);
 }
 
 void grpc_lb_policy_cancel_pick(grpc_exec_ctx *exec_ctx, grpc_lb_policy *policy,
diff --git a/src/core/ext/client_config/lb_policy.h b/src/core/ext/client_config/lb_policy.h
index a2f5446..37c93d7 100644
--- a/src/core/ext/client_config/lb_policy.h
+++ b/src/core/ext/client_config/lb_policy.h
@@ -53,23 +53,38 @@
   grpc_pollset_set *interested_parties;
 };
 
+/** Extra arguments for an LB pick */
+typedef struct grpc_lb_policy_pick_args {
+  /** Parties interested in the pick's progress */
+  grpc_polling_entity *pollent;
+  /** Initial metadata associated with the picking call. */
+  grpc_metadata_batch *initial_metadata;
+  /** See \a GRPC_INITIAL_METADATA_* in grpc_types.h */
+  uint32_t initial_metadata_flags;
+  /** Storage for LB token in \a initial_metadata, or NULL if not used */
+  grpc_linked_mdelem *lb_token_mdelem_storage;
+} grpc_lb_policy_pick_args;
+
 struct grpc_lb_policy_vtable {
   void (*destroy)(grpc_exec_ctx *exec_ctx, grpc_lb_policy *policy);
-
   void (*shutdown)(grpc_exec_ctx *exec_ctx, grpc_lb_policy *policy);
 
-  /** implement grpc_lb_policy_pick */
+  /** \see grpc_lb_policy_pick */
   int (*pick)(grpc_exec_ctx *exec_ctx, grpc_lb_policy *policy,
-              grpc_polling_entity *pollent,
-              grpc_metadata_batch *initial_metadata,
-              uint32_t initial_metadata_flags,
-              grpc_connected_subchannel **target, grpc_closure *on_complete);
+              const grpc_lb_policy_pick_args *pick_args,
+              grpc_connected_subchannel **target, void **user_data,
+              grpc_closure *on_complete);
+
+  /** \see grpc_lb_policy_cancel_pick */
   void (*cancel_pick)(grpc_exec_ctx *exec_ctx, grpc_lb_policy *policy,
                       grpc_connected_subchannel **target);
+
+  /** \see grpc_lb_policy_cancel_picks */
   void (*cancel_picks)(grpc_exec_ctx *exec_ctx, grpc_lb_policy *policy,
                        uint32_t initial_metadata_flags_mask,
                        uint32_t initial_metadata_flags_eq);
 
+  /** \see grpc_lb_policy_ping_one */
   void (*ping_one)(grpc_exec_ctx *exec_ctx, grpc_lb_policy *policy,
                    grpc_closure *closure);
 
@@ -83,8 +98,7 @@
 
   /** call notify when the connectivity state of a channel changes from *state.
       Updates *state with the new state of the policy. Calling with a NULL \a
-      state cancels the subscription.
-      */
+      state cancels the subscription.  */
   void (*notify_on_state_change)(grpc_exec_ctx *exec_ctx,
                                  grpc_lb_policy *policy,
                                  grpc_connectivity_state *state,
@@ -124,26 +138,34 @@
 void grpc_lb_policy_init(grpc_lb_policy *policy,
                          const grpc_lb_policy_vtable *vtable);
 
-/** Given initial metadata in \a initial_metadata, find an appropriate
-    target for this rpc, and 'return' it by calling \a on_complete after setting
-    \a target.
-    Picking can be asynchronous. Any IO should be done under \a pollent. */
+/** Find an appropriate target for this call, based on \a pick_args.
+    Picking can be synchronous or asynchronous. In the synchronous case, when a
+    pick is readily available, it'll be returned in \a target and a non-zero
+    value will be returned.
+    In the asynchronous case, zero is returned and \a on_complete will be called
+    once \a target and \a user_data have been set. Any IO should be done under
+    \a pick_args->pollent. The opaque \a user_data output argument corresponds
+    to information that may need be propagated from the LB policy. It may be
+    NULL. Errors are signaled by receiving a NULL \a *target. */
 int grpc_lb_policy_pick(grpc_exec_ctx *exec_ctx, grpc_lb_policy *policy,
-                        grpc_polling_entity *pollent,
-                        grpc_metadata_batch *initial_metadata,
-                        uint32_t initial_metadata_flags,
-                        grpc_connected_subchannel **target,
+                        const grpc_lb_policy_pick_args *pick_args,
+                        grpc_connected_subchannel **target, void **user_data,
                         grpc_closure *on_complete);
 
+/** Perform a connected subchannel ping (see \a grpc_connected_subchannel_ping)
+    against one of the connected subchannels managed by \a policy. */
 void grpc_lb_policy_ping_one(grpc_exec_ctx *exec_ctx, grpc_lb_policy *policy,
                              grpc_closure *closure);
 
+/** Cancel picks for \a target.
+    The \a on_complete callback of the pending picks will be invoked with \a
+    *target set to NULL. */
 void grpc_lb_policy_cancel_pick(grpc_exec_ctx *exec_ctx, grpc_lb_policy *policy,
                                 grpc_connected_subchannel **target);
 
-/** Cancel all pending picks which have:
-    (initial_metadata_flags & initial_metadata_flags_mask) ==
-         initial_metadata_flags_eq */
+/** Cancel all pending picks for which their \a initial_metadata_flags (as given
+    in the call to \a grpc_lb_policy_pick) matches \a initial_metadata_flags_eq
+    when AND'd with \a initial_metadata_flags_mask */
 void grpc_lb_policy_cancel_picks(grpc_exec_ctx *exec_ctx,
                                  grpc_lb_policy *policy,
                                  uint32_t initial_metadata_flags_mask,
diff --git a/src/core/ext/client_config/lb_policy_factory.h b/src/core/ext/client_config/lb_policy_factory.h
index da1de35..7191ca7 100644
--- a/src/core/ext/client_config/lb_policy_factory.h
+++ b/src/core/ext/client_config/lb_policy_factory.h
@@ -47,8 +47,19 @@
   const grpc_lb_policy_factory_vtable *vtable;
 };
 
+/** A resolved address alongside any LB related information associated with it.
+ * \a user_data, if not NULL, contains opaque data meant to be consumed by the
+ * gRPC LB policy. Note that no all LB policies support \a user_data as input.
+ * Those who don't will simply ignore it and will correspondingly return NULL in
+ * their namesake pick() output argument. */
+typedef struct grpc_lb_address {
+  grpc_resolved_address *resolved_address;
+  void *user_data;
+} grpc_lb_address;
+
 typedef struct grpc_lb_policy_args {
-  grpc_resolved_addresses *addresses;
+  grpc_lb_address *addresses;
+  size_t num_addresses;
   grpc_client_channel_factory *client_channel_factory;
 } grpc_lb_policy_args;
 
diff --git a/src/core/ext/client_config/subchannel.c b/src/core/ext/client_config/subchannel.c
index df35904..2c4364b 100644
--- a/src/core/ext/client_config/subchannel.c
+++ b/src/core/ext/client_config/subchannel.c
@@ -504,14 +504,13 @@
                                           grpc_pollset_set *interested_parties,
                                           grpc_connectivity_state *state,
                                           grpc_closure *closure) {
-  grpc_transport_op op;
+  grpc_transport_op *op = grpc_make_transport_op(NULL);
   grpc_channel_element *elem;
-  memset(&op, 0, sizeof(op));
-  op.connectivity_state = state;
-  op.on_connectivity_state_change = closure;
-  op.bind_pollset_set = interested_parties;
+  op->connectivity_state = state;
+  op->on_connectivity_state_change = closure;
+  op->bind_pollset_set = interested_parties;
   elem = grpc_channel_stack_element(CHANNEL_STACK_FROM_CONNECTION(con), 0);
-  elem->filter->start_transport_op(exec_ctx, elem, &op);
+  elem->filter->start_transport_op(exec_ctx, elem, op);
 }
 
 void grpc_connected_subchannel_notify_on_state_change(
@@ -525,12 +524,11 @@
 void grpc_connected_subchannel_ping(grpc_exec_ctx *exec_ctx,
                                     grpc_connected_subchannel *con,
                                     grpc_closure *closure) {
-  grpc_transport_op op;
+  grpc_transport_op *op = grpc_make_transport_op(NULL);
   grpc_channel_element *elem;
-  memset(&op, 0, sizeof(op));
-  op.send_ping = closure;
+  op->send_ping = closure;
   elem = grpc_channel_stack_element(CHANNEL_STACK_FROM_CONNECTION(con), 0);
-  elem->filter->start_transport_op(exec_ctx, elem, &op);
+  elem->filter->start_transport_op(exec_ctx, elem, op);
 }
 
 static void publish_transport_locked(grpc_exec_ctx *exec_ctx,
diff --git a/src/core/ext/lb_policy/grpclb/grpclb.c b/src/core/ext/lb_policy/grpclb/grpclb.c
index af913d8..c6dfba0 100644
--- a/src/core/ext/lb_policy/grpclb/grpclb.c
+++ b/src/core/ext/lb_policy/grpclb/grpclb.c
@@ -76,9 +76,9 @@
  *    operations in progress over the old RR instance. This is done by
  *    decreasing the reference count on the old policy. The moment no more
  *    references are held on the old RR policy, it'll be destroyed and \a
- *    rr_connectivity_changed notified with a \a GRPC_CHANNEL_SHUTDOWN state.
- *    At this point we can transition to a new RR instance safely, which is done
- *    once again via \a rr_handover().
+ *    glb_rr_connectivity_changed notified with a \a GRPC_CHANNEL_SHUTDOWN
+ *    state. At this point we can transition to a new RR instance safely, which
+ *    is done once again via \a rr_handover().
  *
  *
  * Once a RR policy instance is in place (and getting updated as described),
@@ -96,6 +96,8 @@
  * - Implement LB service forwarding (point 2c. in the doc's diagram).
  */
 
+#include <errno.h>
+
 #include <string.h>
 
 #include <grpc/byte_buffer_reader.h>
@@ -109,18 +111,57 @@
 #include "src/core/ext/client_config/parse_address.h"
 #include "src/core/ext/lb_policy/grpclb/grpclb.h"
 #include "src/core/ext/lb_policy/grpclb/load_balancer_api.h"
+#include "src/core/lib/iomgr/sockaddr.h"
 #include "src/core/lib/iomgr/sockaddr_utils.h"
 #include "src/core/lib/support/string.h"
 #include "src/core/lib/surface/call.h"
 #include "src/core/lib/surface/channel.h"
+#include "src/core/lib/transport/static_metadata.h"
 
 int grpc_lb_glb_trace = 0;
 
+static void lb_addrs_destroy(grpc_lb_address *lb_addresses,
+                             size_t num_addresses) {
+  /* free "resolved" addresses memblock */
+  gpr_free(lb_addresses->resolved_address);
+  for (size_t i = 0; i < num_addresses; ++i) {
+    if (lb_addresses[i].user_data != NULL) {
+      GRPC_MDELEM_UNREF(lb_addresses[i].user_data);
+    }
+  }
+  gpr_free(lb_addresses);
+}
+
+/* add lb_token of selected subchannel (address) to the call's initial
+ * metadata */
+static void initial_metadata_add_lb_token(
+    grpc_metadata_batch *initial_metadata,
+    grpc_linked_mdelem *lb_token_mdelem_storage, grpc_mdelem *lb_token) {
+  GPR_ASSERT(lb_token_mdelem_storage != NULL);
+  GPR_ASSERT(lb_token != NULL);
+  grpc_metadata_batch_add_tail(initial_metadata, lb_token_mdelem_storage,
+                               lb_token);
+}
+
 typedef struct wrapped_rr_closure_arg {
   /* the original closure. Usually a on_complete/notify cb for pick() and ping()
    * calls against the internal RR instance, respectively. */
   grpc_closure *wrapped_closure;
 
+  /* the pick's initial metadata, kept in order to append the LB token for the
+   * pick */
+  grpc_metadata_batch *initial_metadata;
+
+  /* the picked target, used to determine which LB token to add to the pick's
+   * initial metadata */
+  grpc_connected_subchannel **target;
+
+  /* the LB token associated with the pick */
+  grpc_mdelem *lb_token;
+
+  /* storage for the lb token initial metadata mdelem */
+  grpc_linked_mdelem *lb_token_mdelem_storage;
+
   /* The RR instance related to the closure */
   grpc_lb_policy *rr_policy;
 
@@ -141,9 +182,20 @@
               (intptr_t)wc_arg->rr_policy);
     }
     GRPC_LB_POLICY_UNREF(exec_ctx, wc_arg->rr_policy, "wrapped_rr_closure");
+
+    /* if target is NULL, no pick has been made by the RR policy (eg, all
+     * addresses failed to connect). There won't be any user_data/token
+     * available */
+    if (wc_arg->target != NULL) {
+      initial_metadata_add_lb_token(wc_arg->initial_metadata,
+                                    wc_arg->lb_token_mdelem_storage,
+                                    GRPC_MDELEM_REF(wc_arg->lb_token));
+    }
   }
   GPR_ASSERT(wc_arg->wrapped_closure != NULL);
-  grpc_exec_ctx_sched(exec_ctx, wc_arg->wrapped_closure, error, NULL);
+
+  grpc_exec_ctx_sched(exec_ctx, wc_arg->wrapped_closure, GRPC_ERROR_REF(error),
+                      NULL);
   gpr_free(wc_arg->owning_pending_node);
 }
 
@@ -164,6 +216,9 @@
   /* the initial metadata for the pick. See grpc_lb_policy_pick() */
   grpc_metadata_batch *initial_metadata;
 
+  /* storage for the lb token initial metadata mdelem */
+  grpc_linked_mdelem *lb_token_mdelem_storage;
+
   /* bitmask passed to pick() and used for selective cancelling. See
    * grpc_lb_policy_cancel_picks() */
   uint32_t initial_metadata_flags;
@@ -180,20 +235,24 @@
   wrapped_rr_closure_arg wrapped_on_complete_arg;
 } pending_pick;
 
-static void add_pending_pick(pending_pick **root, grpc_polling_entity *pollent,
-                             grpc_metadata_batch *initial_metadata,
-                             uint32_t initial_metadata_flags,
+static void add_pending_pick(pending_pick **root,
+                             const grpc_lb_policy_pick_args *pick_args,
                              grpc_connected_subchannel **target,
                              grpc_closure *on_complete) {
   pending_pick *pp = gpr_malloc(sizeof(*pp));
   memset(pp, 0, sizeof(pending_pick));
   memset(&pp->wrapped_on_complete_arg, 0, sizeof(wrapped_rr_closure_arg));
   pp->next = *root;
-  pp->pollent = pollent;
+  pp->pollent = pick_args->pollent;
   pp->target = target;
-  pp->initial_metadata = initial_metadata;
-  pp->initial_metadata_flags = initial_metadata_flags;
+  pp->initial_metadata = pick_args->initial_metadata;
+  pp->initial_metadata_flags = pick_args->initial_metadata_flags;
+  pp->lb_token_mdelem_storage = pick_args->lb_token_mdelem_storage;
   pp->wrapped_on_complete_arg.wrapped_closure = on_complete;
+  pp->wrapped_on_complete_arg.target = target;
+  pp->wrapped_on_complete_arg.initial_metadata = pick_args->initial_metadata;
+  pp->wrapped_on_complete_arg.lb_token_mdelem_storage =
+      pick_args->lb_token_mdelem_storage;
   grpc_closure_init(&pp->wrapped_on_complete, wrapped_rr_closure,
                     &pp->wrapped_on_complete_arg);
   *root = pp;
@@ -252,6 +311,12 @@
    * response has arrived. */
   grpc_grpclb_serverlist *serverlist;
 
+  /** total number of valid addresses received in \a serverlist */
+  size_t num_ok_serverlist_addresses;
+
+  /** LB addresses from \a serverlist, \a num_ok_serverlist_addresses of them */
+  grpc_lb_address *lb_addresses;
+
   /** list of picks that are waiting on RR's policy connectivity */
   pending_pick *pending_picks;
 
@@ -279,58 +344,142 @@
   glb_lb_policy *glb_policy;
 };
 
+static bool is_server_valid(const grpc_grpclb_server *server, size_t idx,
+                            bool log) {
+  const grpc_grpclb_ip_address *ip = &server->ip_address;
+  if (server->port >> 16 != 0) {
+    if (log) {
+      gpr_log(GPR_ERROR,
+              "Invalid port '%d' at index %zu of serverlist. Ignoring.",
+              server->port, idx);
+    }
+    return false;
+  }
+
+  if (ip->size != 4 && ip->size != 16) {
+    if (log) {
+      gpr_log(GPR_ERROR,
+              "Expected IP to be 4 or 16 bytes, got %d at index %zu of "
+              "serverlist. Ignoring",
+              ip->size, idx);
+    }
+    return false;
+  }
+  return true;
+}
+
+/* populate \a addresses according to \a serverlist. Returns the number of
+ * addresses successfully parsed and added to \a addresses */
+static size_t process_serverlist(const grpc_grpclb_serverlist *serverlist,
+                                 grpc_lb_address **lb_addresses) {
+  size_t num_valid = 0;
+  /* first pass: count how many are valid in order to allocate the necessary
+   * memory in a single block */
+  for (size_t i = 0; i < serverlist->num_servers; ++i) {
+    if (is_server_valid(serverlist->servers[i], i, true)) ++num_valid;
+  }
+  if (num_valid == 0) {
+    return 0;
+  }
+
+  /* allocate the memory block for the "resolved" addresses. */
+  grpc_resolved_address *r_addrs_memblock =
+      gpr_malloc(sizeof(grpc_resolved_address) * num_valid);
+  memset(r_addrs_memblock, 0, sizeof(grpc_resolved_address) * num_valid);
+  grpc_lb_address *lb_addrs = gpr_malloc(sizeof(grpc_lb_address) * num_valid);
+  memset(lb_addrs, 0, sizeof(grpc_lb_address) * num_valid);
+
+  /* second pass: actually populate the addresses and LB tokens (aka user data
+   * to the outside world) to be read by the RR policy during its creation.
+   * Given that the validity tests are very cheap, they are performed again
+   * instead of marking the valid ones during the first pass, as this would
+   * incurr in an allocation due to the arbitrary number of server */
+  size_t addr_idx = 0;
+  for (size_t sl_idx = 0; sl_idx < serverlist->num_servers; ++sl_idx) {
+    GPR_ASSERT(addr_idx < num_valid);
+    const grpc_grpclb_server *server = serverlist->servers[sl_idx];
+    if (!is_server_valid(serverlist->servers[sl_idx], sl_idx, false)) continue;
+    grpc_lb_address *const lb_addr = &lb_addrs[addr_idx];
+
+    /* address processing */
+    const uint16_t netorder_port = htons((uint16_t)server->port);
+    /* the addresses are given in binary format (a in(6)_addr struct) in
+     * server->ip_address.bytes. */
+    const grpc_grpclb_ip_address *ip = &server->ip_address;
+
+    lb_addr->resolved_address = &r_addrs_memblock[addr_idx];
+    struct sockaddr_storage *sa =
+        (struct sockaddr_storage *)lb_addr->resolved_address->addr;
+    size_t *sa_len = &lb_addr->resolved_address->len;
+    *sa_len = 0;
+    if (ip->size == 4) {
+      struct sockaddr_in *addr4 = (struct sockaddr_in *)sa;
+      *sa_len = sizeof(struct sockaddr_in);
+      memset(addr4, 0, *sa_len);
+      addr4->sin_family = AF_INET;
+      memcpy(&addr4->sin_addr, ip->bytes, ip->size);
+      addr4->sin_port = netorder_port;
+    } else if (ip->size == 16) {
+      struct sockaddr_in6 *addr6 = (struct sockaddr_in6 *)sa;
+      *sa_len = sizeof(struct sockaddr_in6);
+      memset(addr6, 0, *sa_len);
+      addr6->sin6_family = AF_INET;
+      memcpy(&addr6->sin6_addr, ip->bytes, ip->size);
+      addr6->sin6_port = netorder_port;
+    }
+    GPR_ASSERT(*sa_len > 0);
+
+    /* lb token processing */
+    if (server->has_load_balance_token) {
+      const size_t lb_token_size =
+          GPR_ARRAY_SIZE(server->load_balance_token) - 1;
+      grpc_mdstr *lb_token_mdstr = grpc_mdstr_from_buffer(
+          (uint8_t *)server->load_balance_token, lb_token_size);
+      lb_addr->user_data = grpc_mdelem_from_metadata_strings(
+          GRPC_MDSTR_LOAD_REPORTING_INITIAL, lb_token_mdstr);
+    } else {
+      gpr_log(GPR_ERROR,
+              "Missing LB token for backend address '%s'. The empty token will "
+              "be used instead",
+              grpc_sockaddr_to_uri((struct sockaddr *)sa));
+      lb_addr->user_data = GRPC_MDELEM_LOAD_REPORTING_INITIAL_EMPTY;
+    }
+    ++addr_idx;
+  }
+  GPR_ASSERT(addr_idx == num_valid);
+  *lb_addresses = lb_addrs;
+  return num_valid;
+}
+
 static grpc_lb_policy *create_rr(grpc_exec_ctx *exec_ctx,
                                  const grpc_grpclb_serverlist *serverlist,
                                  glb_lb_policy *glb_policy) {
-  /* TODO(dgq): support mixed ip version */
   GPR_ASSERT(serverlist != NULL && serverlist->num_servers > 0);
-  char **host_ports = gpr_malloc(sizeof(char *) * serverlist->num_servers);
-  for (size_t i = 0; i < serverlist->num_servers; ++i) {
-    gpr_join_host_port(&host_ports[i], serverlist->servers[i]->ip_address,
-                       serverlist->servers[i]->port);
-  }
-
-  size_t uri_path_len;
-  char *concat_ipports = gpr_strjoin_sep(
-      (const char **)host_ports, serverlist->num_servers, ",", &uri_path_len);
 
   grpc_lb_policy_args args;
+  memset(&args, 0, sizeof(args));
   args.client_channel_factory = glb_policy->cc_factory;
-  args.addresses = gpr_malloc(sizeof(grpc_resolved_addresses));
-  args.addresses->naddrs = serverlist->num_servers;
-  args.addresses->addrs =
-      gpr_malloc(sizeof(grpc_resolved_address) * args.addresses->naddrs);
-  size_t out_addrs_idx = 0;
-  for (size_t i = 0; i < serverlist->num_servers; ++i) {
-    grpc_uri uri;
-    struct sockaddr_storage sa;
-    size_t sa_len;
-    uri.path = host_ports[i];
-    if (parse_ipv4(&uri, &sa, &sa_len)) { /* TODO(dgq): add support for ipv6 */
-      memcpy(args.addresses->addrs[out_addrs_idx].addr, &sa, sa_len);
-      args.addresses->addrs[out_addrs_idx].len = sa_len;
-      ++out_addrs_idx;
-    } else {
-      gpr_log(GPR_ERROR, "Invalid LB service address '%s', ignoring.",
-              host_ports[i]);
-    }
-  }
+  const size_t num_ok_addresses =
+      process_serverlist(serverlist, &args.addresses);
+  args.num_addresses = num_ok_addresses;
 
   grpc_lb_policy *rr = grpc_lb_policy_create(exec_ctx, "round_robin", &args);
 
-  gpr_free(concat_ipports);
-  for (size_t i = 0; i < serverlist->num_servers; i++) {
-    gpr_free(host_ports[i]);
+  if (glb_policy->lb_addresses != NULL) {
+    /* dispose of the previous version */
+    lb_addrs_destroy(glb_policy->lb_addresses,
+                     glb_policy->num_ok_serverlist_addresses);
   }
-  gpr_free(host_ports);
-  gpr_free(args.addresses->addrs);
-  gpr_free(args.addresses);
+  glb_policy->num_ok_serverlist_addresses = num_ok_addresses;
+  glb_policy->lb_addresses = args.addresses;
+
   return rr;
 }
 
 static void rr_handover(grpc_exec_ctx *exec_ctx, glb_lb_policy *glb_policy,
                         grpc_error *error) {
-  GRPC_ERROR_REF(error);
+  GPR_ASSERT(glb_policy->serverlist != NULL &&
+             glb_policy->serverlist->num_servers > 0);
   glb_policy->rr_policy =
       create_rr(exec_ctx, glb_policy->serverlist, glb_policy);
 
@@ -345,8 +494,8 @@
       exec_ctx, glb_policy->rr_policy, &glb_policy->rr_connectivity->state,
       &glb_policy->rr_connectivity->on_change);
   grpc_connectivity_state_set(exec_ctx, &glb_policy->state_tracker,
-                              glb_policy->rr_connectivity->state, error,
-                              "rr_handover");
+                              glb_policy->rr_connectivity->state,
+                              GRPC_ERROR_REF(error), "rr_handover");
   grpc_lb_policy_exit_idle(exec_ctx, glb_policy->rr_policy);
 
   /* flush pending ops */
@@ -359,9 +508,12 @@
       gpr_log(GPR_INFO, "Pending pick about to PICK from 0x%" PRIxPTR "",
               (intptr_t)glb_policy->rr_policy);
     }
-    grpc_lb_policy_pick(exec_ctx, glb_policy->rr_policy, pp->pollent,
-                        pp->initial_metadata, pp->initial_metadata_flags,
-                        pp->target, &pp->wrapped_on_complete);
+    const grpc_lb_policy_pick_args pick_args = {
+        pp->pollent, pp->initial_metadata, pp->initial_metadata_flags,
+        pp->lb_token_mdelem_storage};
+    grpc_lb_policy_pick(exec_ctx, glb_policy->rr_policy, &pick_args, pp->target,
+                        (void **)&pp->wrapped_on_complete_arg.lb_token,
+                        &pp->wrapped_on_complete);
     pp->wrapped_on_complete_arg.owning_pending_node = pp;
   }
 
@@ -378,13 +530,13 @@
                             &pping->wrapped_notify);
     pping->wrapped_notify_arg.owning_pending_node = pping;
   }
-  GRPC_ERROR_UNREF(error);
 }
 
-static void rr_connectivity_changed(grpc_exec_ctx *exec_ctx, void *arg,
-                                    grpc_error *error) {
+static void glb_rr_connectivity_changed(grpc_exec_ctx *exec_ctx, void *arg,
+                                        grpc_error *error) {
   rr_connectivity_data *rr_conn_data = arg;
   glb_lb_policy *glb_policy = rr_conn_data->glb_policy;
+
   if (rr_conn_data->state == GRPC_CHANNEL_SHUTDOWN) {
     if (glb_policy->serverlist != NULL) {
       /* a RR policy is shutting down but there's a serverlist available ->
@@ -398,8 +550,8 @@
     if (error == GRPC_ERROR_NONE) {
       /* RR not shutting down. Mimic the RR's policy state */
       grpc_connectivity_state_set(exec_ctx, &glb_policy->state_tracker,
-                                  rr_conn_data->state, error,
-                                  "rr_connectivity_changed");
+                                  rr_conn_data->state, GRPC_ERROR_REF(error),
+                                  "glb_rr_connectivity_changed");
       /* resubscribe */
       grpc_lb_policy_notify_on_state_change(exec_ctx, glb_policy->rr_policy,
                                             &rr_conn_data->state,
@@ -408,7 +560,6 @@
       gpr_free(rr_conn_data);
     }
   }
-  GRPC_ERROR_UNREF(error);
 }
 
 static grpc_lb_policy *glb_create(grpc_exec_ctx *exec_ctx,
@@ -418,31 +569,43 @@
   memset(glb_policy, 0, sizeof(*glb_policy));
 
   /* All input addresses in args->addresses come from a resolver that claims
-   * they are LB services. It's the resolver's responsibility to make sure this
+   * they are LB services. It's the resolver's responsibility to make sure
+   * this
    * policy is only instantiated and used in that case.
    *
    * Create a client channel over them to communicate with a LB service */
   glb_policy->cc_factory = args->client_channel_factory;
   GPR_ASSERT(glb_policy->cc_factory != NULL);
-  if (args->addresses->naddrs == 0) {
+  if (args->num_addresses == 0) {
     return NULL;
   }
 
-  /* construct a target from the args->addresses, in the form
+  if (args->addresses[0].user_data != NULL) {
+    gpr_log(GPR_ERROR,
+            "This LB policy doesn't support user data. It will be ignored");
+  }
+
+  /* construct a target from the addresses in args, given in the form
    * ipvX://ip1:port1,ip2:port2,...
    * TODO(dgq): support mixed ip version */
-  char **addr_strs = gpr_malloc(sizeof(char *) * args->addresses->naddrs);
-  addr_strs[0] =
-      grpc_sockaddr_to_uri((const struct sockaddr *)&args->addresses->addrs[0]);
-  for (size_t i = 1; i < args->addresses->naddrs; i++) {
-    GPR_ASSERT(grpc_sockaddr_to_string(
-                   &addr_strs[i],
-                   (const struct sockaddr *)&args->addresses->addrs[i],
-                   true) == 0);
+  char **addr_strs = gpr_malloc(sizeof(char *) * args->num_addresses);
+  addr_strs[0] = grpc_sockaddr_to_uri(
+      (const struct sockaddr *)&args->addresses[0].resolved_address->addr);
+  for (size_t i = 1; i < args->num_addresses; i++) {
+    if (args->addresses[i].user_data != NULL) {
+      gpr_log(GPR_ERROR,
+              "This LB policy doesn't support user data. It will be ignored");
+    }
+
+    GPR_ASSERT(
+        grpc_sockaddr_to_string(
+            &addr_strs[i],
+            (const struct sockaddr *)&args->addresses[i].resolved_address->addr,
+            true) == 0);
   }
   size_t uri_path_len;
   char *target_uri_str = gpr_strjoin_sep(
-      (const char **)addr_strs, args->addresses->naddrs, ",", &uri_path_len);
+      (const char **)addr_strs, args->num_addresses, ",", &uri_path_len);
 
   /* will pick using pick_first */
   glb_policy->lb_channel = grpc_client_channel_factory_create_channel(
@@ -450,7 +613,7 @@
       GRPC_CLIENT_CHANNEL_TYPE_LOAD_BALANCING, NULL);
 
   gpr_free(target_uri_str);
-  for (size_t i = 0; i < args->addresses->naddrs; i++) {
+  for (size_t i = 0; i < args->num_addresses; i++) {
     gpr_free(addr_strs[i]);
   }
   gpr_free(addr_strs);
@@ -463,7 +626,7 @@
   rr_connectivity_data *rr_connectivity =
       gpr_malloc(sizeof(rr_connectivity_data));
   memset(rr_connectivity, 0, sizeof(rr_connectivity_data));
-  grpc_closure_init(&rr_connectivity->on_change, rr_connectivity_changed,
+  grpc_closure_init(&rr_connectivity->on_change, glb_rr_connectivity_changed,
                     rr_connectivity);
   rr_connectivity->glb_policy = glb_policy;
   glb_policy->rr_connectivity = rr_connectivity;
@@ -486,6 +649,9 @@
     grpc_grpclb_destroy_serverlist(glb_policy->serverlist);
   }
   gpr_mu_destroy(&glb_policy->mu);
+
+  lb_addrs_destroy(glb_policy->lb_addresses,
+                   glb_policy->num_ok_serverlist_addresses);
   gpr_free(glb_policy);
 }
 
@@ -546,7 +712,6 @@
       *target = NULL;
       grpc_exec_ctx_sched(exec_ctx, &pp->wrapped_on_complete,
                           GRPC_ERROR_CANCELLED, NULL);
-      gpr_free(pp);
     } else {
       pp->next = glb_policy->pending_picks;
       glb_policy->pending_picks = pp;
@@ -576,7 +741,6 @@
           exec_ctx, pp->pollent, glb_policy->base.interested_parties);
       grpc_exec_ctx_sched(exec_ctx, &pp->wrapped_on_complete,
                           GRPC_ERROR_CANCELLED, NULL);
-      gpr_free(pp);
     } else {
       pp->next = glb_policy->pending_picks;
       glb_policy->pending_picks = pp;
@@ -603,12 +767,21 @@
 }
 
 static int glb_pick(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol,
-                    grpc_polling_entity *pollent,
-                    grpc_metadata_batch *initial_metadata,
-                    uint32_t initial_metadata_flags,
-                    grpc_connected_subchannel **target,
+                    const grpc_lb_policy_pick_args *pick_args,
+                    grpc_connected_subchannel **target, void **user_data,
                     grpc_closure *on_complete) {
   glb_lb_policy *glb_policy = (glb_lb_policy *)pol;
+
+  if (pick_args->lb_token_mdelem_storage == NULL) {
+    *target = NULL;
+    grpc_exec_ctx_sched(
+        exec_ctx, on_complete,
+        GRPC_ERROR_CREATE("No mdelem storage for the LB token. Load reporting "
+                          "won't work without it. Failing"),
+        NULL);
+    return 1;
+  }
+
   gpr_mu_lock(&glb_policy->mu);
   int r;
 
@@ -620,29 +793,36 @@
     GRPC_LB_POLICY_REF(glb_policy->rr_policy, "glb_pick");
     memset(&glb_policy->wc_arg, 0, sizeof(wrapped_rr_closure_arg));
     glb_policy->wc_arg.rr_policy = glb_policy->rr_policy;
+    glb_policy->wc_arg.target = target;
     glb_policy->wc_arg.wrapped_closure = on_complete;
+    glb_policy->wc_arg.lb_token_mdelem_storage =
+        pick_args->lb_token_mdelem_storage;
+    glb_policy->wc_arg.initial_metadata = pick_args->initial_metadata;
+    glb_policy->wc_arg.owning_pending_node = NULL;
     grpc_closure_init(&glb_policy->wrapped_on_complete, wrapped_rr_closure,
                       &glb_policy->wc_arg);
-    r = grpc_lb_policy_pick(exec_ctx, glb_policy->rr_policy, pollent,
-                            initial_metadata, initial_metadata_flags, target,
+
+    r = grpc_lb_policy_pick(exec_ctx, glb_policy->rr_policy, pick_args, target,
+                            (void **)&glb_policy->wc_arg.lb_token,
                             &glb_policy->wrapped_on_complete);
     if (r != 0) {
-      /* the call to grpc_lb_policy_pick has been sychronous. Unreffing the RR
-       * policy and notify the original callback */
-      glb_policy->wc_arg.wrapped_closure = NULL;
+      /* synchronous grpc_lb_policy_pick call. Unref the RR policy. */
       if (grpc_lb_glb_trace) {
         gpr_log(GPR_INFO, "Unreffing RR (0x%" PRIxPTR ")",
                 (intptr_t)glb_policy->wc_arg.rr_policy);
       }
       GRPC_LB_POLICY_UNREF(exec_ctx, glb_policy->wc_arg.rr_policy, "glb_pick");
-      grpc_exec_ctx_sched(exec_ctx, glb_policy->wc_arg.wrapped_closure,
-                          GRPC_ERROR_NONE, NULL);
+
+      /* add the load reporting initial metadata */
+      initial_metadata_add_lb_token(
+          pick_args->initial_metadata, pick_args->lb_token_mdelem_storage,
+          GRPC_MDELEM_REF(glb_policy->wc_arg.lb_token));
     }
   } else {
-    grpc_polling_entity_add_to_pollset_set(exec_ctx, pollent,
+    grpc_polling_entity_add_to_pollset_set(exec_ctx, pick_args->pollent,
                                            glb_policy->base.interested_parties);
-    add_pending_pick(&glb_policy->pending_picks, pollent, initial_metadata,
-                     initial_metadata_flags, target, on_complete);
+    add_pending_pick(&glb_policy->pending_picks, pick_args, target,
+                     on_complete);
 
     if (!glb_policy->started_picking) {
       start_picking(exec_ctx, glb_policy);
@@ -702,9 +882,6 @@
   /* called once initial metadata's been sent */
   grpc_closure md_sent;
 
-  /* called once initial metadata's been received */
-  grpc_closure md_rcvd;
-
   /* called once the LoadBalanceRequest has been sent to the LB server. See
    * src/proto/grpc/.../load_balancer.proto */
   grpc_closure req_sent;
@@ -741,7 +918,6 @@
 } lb_client_data;
 
 static void md_sent_cb(grpc_exec_ctx *exec_ctx, void *arg, grpc_error *error);
-static void md_recv_cb(grpc_exec_ctx *exec_ctx, void *arg, grpc_error *error);
 static void req_sent_cb(grpc_exec_ctx *exec_ctx, void *arg, grpc_error *error);
 static void res_recv_cb(grpc_exec_ctx *exec_ctx, void *arg, grpc_error *error);
 static void close_sent_cb(grpc_exec_ctx *exec_ctx, void *arg,
@@ -756,7 +932,6 @@
   gpr_mu_init(&lb_client->mu);
   grpc_closure_init(&lb_client->md_sent, md_sent_cb, lb_client);
 
-  grpc_closure_init(&lb_client->md_rcvd, md_recv_cb, lb_client);
   grpc_closure_init(&lb_client->req_sent, req_sent_cb, lb_client);
   grpc_closure_init(&lb_client->res_rcvd, res_recv_cb, lb_client);
   grpc_closure_init(&lb_client->close_sent, close_sent_cb, lb_client);
@@ -855,23 +1030,6 @@
   grpc_op ops[1];
   memset(ops, 0, sizeof(ops));
   grpc_op *op = ops;
-  op->op = GRPC_OP_RECV_INITIAL_METADATA;
-  op->data.recv_initial_metadata = &lb_client->initial_metadata_recv;
-  op->flags = 0;
-  op->reserved = NULL;
-  op++;
-  grpc_call_error call_error = grpc_call_start_batch_and_execute(
-      exec_ctx, lb_client->lb_call, ops, (size_t)(op - ops),
-      &lb_client->md_rcvd);
-  GPR_ASSERT(GRPC_CALL_OK == call_error);
-}
-
-static void md_recv_cb(grpc_exec_ctx *exec_ctx, void *arg, grpc_error *error) {
-  lb_client_data *lb_client = arg;
-  GPR_ASSERT(lb_client->lb_call);
-  grpc_op ops[1];
-  memset(ops, 0, sizeof(ops));
-  grpc_op *op = ops;
 
   op->op = GRPC_OP_SEND_MESSAGE;
   op->data.send_message = lb_client->request_payload;
@@ -886,11 +1044,18 @@
 
 static void req_sent_cb(grpc_exec_ctx *exec_ctx, void *arg, grpc_error *error) {
   lb_client_data *lb_client = arg;
+  GPR_ASSERT(lb_client->lb_call);
 
-  grpc_op ops[1];
+  grpc_op ops[2];
   memset(ops, 0, sizeof(ops));
   grpc_op *op = ops;
 
+  op->op = GRPC_OP_RECV_INITIAL_METADATA;
+  op->data.recv_initial_metadata = &lb_client->initial_metadata_recv;
+  op->flags = 0;
+  op->reserved = NULL;
+  op++;
+
   op->op = GRPC_OP_RECV_MESSAGE;
   op->data.recv_message = &lb_client->response_payload;
   op->flags = 0;
@@ -909,8 +1074,7 @@
   grpc_op *op = ops;
   if (lb_client->response_payload != NULL) {
     /* Received data from the LB server. Look inside
-     * lb_client->response_payload, for
-     * a serverlist. */
+     * lb_client->response_payload, for a serverlist. */
     grpc_byte_buffer_reader bbr;
     grpc_byte_buffer_reader_init(&bbr, lb_client->response_payload);
     gpr_slice response_slice = grpc_byte_buffer_reader_readall(&bbr);
@@ -947,7 +1111,7 @@
         } else {
           /* unref the RR policy, eventually leading to its substitution with a
            * new one constructed from the received serverlist (see
-           * rr_connectivity_changed) */
+           * glb_rr_connectivity_changed) */
           GRPC_LB_POLICY_UNREF(exec_ctx, lb_client->glb_policy->rr_policy,
                                "serverlist_received");
         }
@@ -1010,8 +1174,8 @@
             lb_client->status, lb_client->status_details,
             lb_client->status_details_capacity);
   }
-  /* TODO(dgq): deal with stream termination properly (fire up another one? fail
-   * the original call?) */
+  /* TODO(dgq): deal with stream termination properly (fire up another one?
+   * fail the original call?) */
 }
 
 /* Code wiring the policy with the rest of the core */
diff --git a/src/core/ext/lb_policy/grpclb/load_balancer_api.c b/src/core/ext/lb_policy/grpclb/load_balancer_api.c
index f4720a1..a888100 100644
--- a/src/core/ext/lb_policy/grpclb/load_balancer_api.c
+++ b/src/core/ext/lb_policy/grpclb/load_balancer_api.c
@@ -57,6 +57,7 @@
   if (dec_arg->first_pass) { /* count how many server do we have */
     grpc_grpclb_server server;
     if (!pb_decode(stream, grpc_lb_v1_Server_fields, &server)) {
+      gpr_log(GPR_ERROR, "nanopb error: %s", PB_GET_ERROR(stream));
       return false;
     }
     dec_arg->num_servers++;
@@ -69,6 +70,7 @@
           gpr_malloc(sizeof(grpc_grpclb_server *) * dec_arg->num_servers);
     }
     if (!pb_decode(stream, grpc_lb_v1_Server_fields, server)) {
+      gpr_log(GPR_ERROR, "nanopb error: %s", PB_GET_ERROR(stream));
       return false;
     }
     dec_arg->servers[dec_arg->decoding_idx++] = server;
@@ -118,6 +120,7 @@
   grpc_grpclb_response res;
   memset(&res, 0, sizeof(grpc_grpclb_response));
   if (!pb_decode(&stream, grpc_lb_v1_LoadBalanceResponse_fields, &res)) {
+    gpr_log(GPR_ERROR, "nanopb error: %s", PB_GET_ERROR(&stream));
     return NULL;
   }
   grpc_grpclb_initial_response *initial_res =
@@ -145,6 +148,7 @@
   arg.first_pass = true;
   status = pb_decode(&stream, grpc_lb_v1_LoadBalanceResponse_fields, &res);
   if (!status) {
+    gpr_log(GPR_ERROR, "nanopb error: %s", PB_GET_ERROR(&stream));
     return NULL;
   }
 
@@ -152,6 +156,7 @@
   status =
       pb_decode(&stream_at_start, grpc_lb_v1_LoadBalanceResponse_fields, &res);
   if (!status) {
+    gpr_log(GPR_ERROR, "nanopb error: %s", PB_GET_ERROR(&stream));
     return NULL;
   }
 
diff --git a/src/core/ext/lb_policy/grpclb/load_balancer_api.h b/src/core/ext/lb_policy/grpclb/load_balancer_api.h
index 9726c87..c1e73d0 100644
--- a/src/core/ext/lb_policy/grpclb/load_balancer_api.h
+++ b/src/core/ext/lb_policy/grpclb/load_balancer_api.h
@@ -45,6 +45,7 @@
 
 #define GRPC_GRPCLB_SERVICE_NAME_MAX_LENGTH 128
 
+typedef grpc_lb_v1_Server_ip_address_t grpc_grpclb_ip_address;
 typedef grpc_lb_v1_LoadBalanceRequest grpc_grpclb_request;
 typedef grpc_lb_v1_InitialLoadBalanceResponse grpc_grpclb_initial_response;
 typedef grpc_lb_v1_Server grpc_grpclb_server;
diff --git a/src/core/ext/lb_policy/grpclb/proto/grpc/lb/v1/load_balancer.pb.c b/src/core/ext/lb_policy/grpclb/proto/grpc/lb/v1/load_balancer.pb.c
index 52e11c4..afecb71 100644
--- a/src/core/ext/lb_policy/grpclb/proto/grpc/lb/v1/load_balancer.pb.c
+++ b/src/core/ext/lb_policy/grpclb/proto/grpc/lb/v1/load_balancer.pb.c
@@ -31,10 +31,11 @@
  *
  */
 /* Automatically generated nanopb constant definitions */
-/* Generated by nanopb-0.3.5-dev */
+/* Generated by nanopb-0.3.7-dev */
 
 #include "src/core/ext/lb_policy/grpclb/proto/grpc/lb/v1/load_balancer.pb.h"
 
+/* @@protoc_insertion_point(includes) */
 #if PB_PROTO_HEADER_VERSION != 30
 #error Regenerate this file with the current version of nanopb generator.
 #endif
@@ -72,8 +73,8 @@
 };
 
 const pb_field_t grpc_lb_v1_InitialLoadBalanceResponse_fields[3] = {
-    PB_FIELD(  2, STRING  , OPTIONAL, STATIC  , FIRST, grpc_lb_v1_InitialLoadBalanceResponse, load_balancer_delegate, load_balancer_delegate, 0),
-    PB_FIELD(  3, MESSAGE , OPTIONAL, STATIC  , OTHER, grpc_lb_v1_InitialLoadBalanceResponse, client_stats_report_interval, load_balancer_delegate, &grpc_lb_v1_Duration_fields),
+    PB_FIELD(  1, STRING  , OPTIONAL, STATIC  , FIRST, grpc_lb_v1_InitialLoadBalanceResponse, load_balancer_delegate, load_balancer_delegate, 0),
+    PB_FIELD(  2, MESSAGE , OPTIONAL, STATIC  , OTHER, grpc_lb_v1_InitialLoadBalanceResponse, client_stats_report_interval, load_balancer_delegate, &grpc_lb_v1_Duration_fields),
     PB_LAST_FIELD
 };
 
@@ -84,7 +85,7 @@
 };
 
 const pb_field_t grpc_lb_v1_Server_fields[5] = {
-    PB_FIELD(  1, STRING  , OPTIONAL, STATIC  , FIRST, grpc_lb_v1_Server, ip_address, ip_address, 0),
+    PB_FIELD(  1, BYTES   , OPTIONAL, STATIC  , FIRST, grpc_lb_v1_Server, ip_address, ip_address, 0),
     PB_FIELD(  2, INT32   , OPTIONAL, STATIC  , OTHER, grpc_lb_v1_Server, port, ip_address, 0),
     PB_FIELD(  3, STRING  , OPTIONAL, STATIC  , OTHER, grpc_lb_v1_Server, load_balance_token, port, 0),
     PB_FIELD(  4, BOOL    , OPTIONAL, STATIC  , OTHER, grpc_lb_v1_Server, drop_request, load_balance_token, 0),
@@ -116,3 +117,4 @@
 #endif
 
 
+/* @@protoc_insertion_point(eof) */
diff --git a/src/core/ext/lb_policy/grpclb/proto/grpc/lb/v1/load_balancer.pb.h b/src/core/ext/lb_policy/grpclb/proto/grpc/lb/v1/load_balancer.pb.h
index 46fe588..53fed22 100644
--- a/src/core/ext/lb_policy/grpclb/proto/grpc/lb/v1/load_balancer.pb.h
+++ b/src/core/ext/lb_policy/grpclb/proto/grpc/lb/v1/load_balancer.pb.h
@@ -31,11 +31,12 @@
  *
  */
 /* Automatically generated nanopb header */
-/* Generated by nanopb-0.3.5-dev */
+/* Generated by nanopb-0.3.7-dev */
 
-#ifndef GRPC_CORE_EXT_LB_POLICY_GRPCLB_PROTO_GRPC_LB_V1_LOAD_BALANCER_PB_H
-#define GRPC_CORE_EXT_LB_POLICY_GRPCLB_PROTO_GRPC_LB_V1_LOAD_BALANCER_PB_H
+#ifndef PB_GRPC_LB_V1_LOAD_BALANCER_PB_H_INCLUDED
+#define PB_GRPC_LB_V1_LOAD_BALANCER_PB_H_INCLUDED
 #include "third_party/nanopb/pb.h"
+/* @@protoc_insertion_point(includes) */
 #if PB_PROTO_HEADER_VERSION != 30
 #error Regenerate this file with the current version of nanopb generator.
 #endif
@@ -52,6 +53,7 @@
     int64_t client_rpc_errors;
     bool has_dropped_requests;
     int64_t dropped_requests;
+/* @@protoc_insertion_point(struct:grpc_lb_v1_ClientStats) */
 } grpc_lb_v1_ClientStats;
 
 typedef struct _grpc_lb_v1_Duration {
@@ -59,22 +61,26 @@
     int64_t seconds;
     bool has_nanos;
     int32_t nanos;
+/* @@protoc_insertion_point(struct:grpc_lb_v1_Duration) */
 } grpc_lb_v1_Duration;
 
 typedef struct _grpc_lb_v1_InitialLoadBalanceRequest {
     bool has_name;
     char name[128];
+/* @@protoc_insertion_point(struct:grpc_lb_v1_InitialLoadBalanceRequest) */
 } grpc_lb_v1_InitialLoadBalanceRequest;
 
+typedef PB_BYTES_ARRAY_T(16) grpc_lb_v1_Server_ip_address_t;
 typedef struct _grpc_lb_v1_Server {
     bool has_ip_address;
-    char ip_address[46];
+    grpc_lb_v1_Server_ip_address_t ip_address;
     bool has_port;
     int32_t port;
     bool has_load_balance_token;
-    char load_balance_token[64];
+    char load_balance_token[65];
     bool has_drop_request;
     bool drop_request;
+/* @@protoc_insertion_point(struct:grpc_lb_v1_Server) */
 } grpc_lb_v1_Server;
 
 typedef struct _grpc_lb_v1_InitialLoadBalanceResponse {
@@ -82,6 +88,7 @@
     char load_balancer_delegate[64];
     bool has_client_stats_report_interval;
     grpc_lb_v1_Duration client_stats_report_interval;
+/* @@protoc_insertion_point(struct:grpc_lb_v1_InitialLoadBalanceResponse) */
 } grpc_lb_v1_InitialLoadBalanceResponse;
 
 typedef struct _grpc_lb_v1_LoadBalanceRequest {
@@ -89,12 +96,14 @@
     grpc_lb_v1_InitialLoadBalanceRequest initial_request;
     bool has_client_stats;
     grpc_lb_v1_ClientStats client_stats;
+/* @@protoc_insertion_point(struct:grpc_lb_v1_LoadBalanceRequest) */
 } grpc_lb_v1_LoadBalanceRequest;
 
 typedef struct _grpc_lb_v1_ServerList {
     pb_callback_t servers;
     bool has_expiration_interval;
     grpc_lb_v1_Duration expiration_interval;
+/* @@protoc_insertion_point(struct:grpc_lb_v1_ServerList) */
 } grpc_lb_v1_ServerList;
 
 typedef struct _grpc_lb_v1_LoadBalanceResponse {
@@ -102,6 +111,7 @@
     grpc_lb_v1_InitialLoadBalanceResponse initial_response;
     bool has_server_list;
     grpc_lb_v1_ServerList server_list;
+/* @@protoc_insertion_point(struct:grpc_lb_v1_LoadBalanceResponse) */
 } grpc_lb_v1_LoadBalanceResponse;
 
 /* Default values for struct fields */
@@ -114,7 +124,7 @@
 #define grpc_lb_v1_LoadBalanceResponse_init_default {false, grpc_lb_v1_InitialLoadBalanceResponse_init_default, false, grpc_lb_v1_ServerList_init_default}
 #define grpc_lb_v1_InitialLoadBalanceResponse_init_default {false, "", false, grpc_lb_v1_Duration_init_default}
 #define grpc_lb_v1_ServerList_init_default       {{{NULL}, NULL}, false, grpc_lb_v1_Duration_init_default}
-#define grpc_lb_v1_Server_init_default           {false, "", false, 0, false, "", false, 0}
+#define grpc_lb_v1_Server_init_default           {false, {0, {0}}, false, 0, false, "", false, 0}
 #define grpc_lb_v1_Duration_init_zero            {false, 0, false, 0}
 #define grpc_lb_v1_LoadBalanceRequest_init_zero  {false, grpc_lb_v1_InitialLoadBalanceRequest_init_zero, false, grpc_lb_v1_ClientStats_init_zero}
 #define grpc_lb_v1_InitialLoadBalanceRequest_init_zero {false, ""}
@@ -122,7 +132,7 @@
 #define grpc_lb_v1_LoadBalanceResponse_init_zero {false, grpc_lb_v1_InitialLoadBalanceResponse_init_zero, false, grpc_lb_v1_ServerList_init_zero}
 #define grpc_lb_v1_InitialLoadBalanceResponse_init_zero {false, "", false, grpc_lb_v1_Duration_init_zero}
 #define grpc_lb_v1_ServerList_init_zero          {{{NULL}, NULL}, false, grpc_lb_v1_Duration_init_zero}
-#define grpc_lb_v1_Server_init_zero              {false, "", false, 0, false, "", false, 0}
+#define grpc_lb_v1_Server_init_zero              {false, {0, {0}}, false, 0, false, "", false, 0}
 
 /* Field tags (for use in manual encoding/decoding) */
 #define grpc_lb_v1_ClientStats_total_requests_tag 1
@@ -135,8 +145,8 @@
 #define grpc_lb_v1_Server_port_tag               2
 #define grpc_lb_v1_Server_load_balance_token_tag 3
 #define grpc_lb_v1_Server_drop_request_tag       4
-#define grpc_lb_v1_InitialLoadBalanceResponse_load_balancer_delegate_tag 2
-#define grpc_lb_v1_InitialLoadBalanceResponse_client_stats_report_interval_tag 3
+#define grpc_lb_v1_InitialLoadBalanceResponse_load_balancer_delegate_tag 1
+#define grpc_lb_v1_InitialLoadBalanceResponse_client_stats_report_interval_tag 2
 #define grpc_lb_v1_LoadBalanceRequest_initial_request_tag 1
 #define grpc_lb_v1_LoadBalanceRequest_client_stats_tag 2
 #define grpc_lb_v1_ServerList_servers_tag        1
@@ -161,7 +171,8 @@
 #define grpc_lb_v1_ClientStats_size              33
 #define grpc_lb_v1_LoadBalanceResponse_size      (98 + grpc_lb_v1_ServerList_size)
 #define grpc_lb_v1_InitialLoadBalanceResponse_size 90
-#define grpc_lb_v1_Server_size                   127
+/* grpc_lb_v1_ServerList_size depends on runtime parameters */
+#define grpc_lb_v1_Server_size                   98
 
 /* Message IDs (where set with "msgid" option) */
 #ifdef PB_MSGID
@@ -174,5 +185,6 @@
 #ifdef __cplusplus
 } /* extern "C" */
 #endif
+/* @@protoc_insertion_point(eof) */
 
 #endif
diff --git a/src/core/ext/lb_policy/pick_first/pick_first.c b/src/core/ext/lb_policy/pick_first/pick_first.c
index 9decf70..9513078 100644
--- a/src/core/ext/lb_policy/pick_first/pick_first.c
+++ b/src/core/ext/lb_policy/pick_first/pick_first.c
@@ -199,10 +199,8 @@
 }
 
 static int pf_pick(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol,
-                   grpc_polling_entity *pollent,
-                   grpc_metadata_batch *initial_metadata,
-                   uint32_t initial_metadata_flags,
-                   grpc_connected_subchannel **target,
+                   const grpc_lb_policy_pick_args *pick_args,
+                   grpc_connected_subchannel **target, void **user_data,
                    grpc_closure *on_complete) {
   pick_first_lb_policy *p = (pick_first_lb_policy *)pol;
   pending_pick *pp;
@@ -225,13 +223,13 @@
     if (!p->started_picking) {
       start_picking(exec_ctx, p);
     }
-    grpc_polling_entity_add_to_pollset_set(exec_ctx, pollent,
+    grpc_polling_entity_add_to_pollset_set(exec_ctx, pick_args->pollent,
                                            p->base.interested_parties);
     pp = gpr_malloc(sizeof(*pp));
     pp->next = p->pending_picks;
-    pp->pollent = pollent;
+    pp->pollent = pick_args->pollent;
     pp->target = target;
-    pp->initial_metadata_flags = initial_metadata_flags;
+    pp->initial_metadata_flags = pick_args->initial_metadata_flags;
     pp->on_complete = on_complete;
     p->pending_picks = pp;
     gpr_mu_unlock(&p->mu);
@@ -443,20 +441,25 @@
   GPR_ASSERT(args->addresses != NULL);
   GPR_ASSERT(args->client_channel_factory != NULL);
 
-  if (args->addresses->naddrs == 0) return NULL;
+  if (args->num_addresses == 0) return NULL;
 
   pick_first_lb_policy *p = gpr_malloc(sizeof(*p));
   memset(p, 0, sizeof(*p));
 
-  p->subchannels =
-      gpr_malloc(sizeof(grpc_subchannel *) * args->addresses->naddrs);
-  memset(p->subchannels, 0, sizeof(*p->subchannels) * args->addresses->naddrs);
+  p->subchannels = gpr_malloc(sizeof(grpc_subchannel *) * args->num_addresses);
+  memset(p->subchannels, 0, sizeof(*p->subchannels) * args->num_addresses);
   grpc_subchannel_args sc_args;
   size_t subchannel_idx = 0;
-  for (size_t i = 0; i < args->addresses->naddrs; i++) {
+  for (size_t i = 0; i < args->num_addresses; i++) {
+    if (args->addresses[i].user_data != NULL) {
+      gpr_log(GPR_ERROR,
+              "This LB policy doesn't support user data. It will be ignored");
+    }
+
     memset(&sc_args, 0, sizeof(grpc_subchannel_args));
-    sc_args.addr = (struct sockaddr *)(args->addresses->addrs[i].addr);
-    sc_args.addr_len = (size_t)args->addresses->addrs[i].len;
+    sc_args.addr =
+        (struct sockaddr *)(args->addresses[i].resolved_address->addr);
+    sc_args.addr_len = (size_t)args->addresses[i].resolved_address->len;
 
     grpc_subchannel *subchannel = grpc_client_channel_factory_create_subchannel(
         exec_ctx, args->client_channel_factory, &sc_args);
diff --git a/src/core/ext/lb_policy/round_robin/round_robin.c b/src/core/ext/lb_policy/round_robin/round_robin.c
index 7bcf608..a9c37ac 100644
--- a/src/core/ext/lb_policy/round_robin/round_robin.c
+++ b/src/core/ext/lb_policy/round_robin/round_robin.c
@@ -66,6 +66,7 @@
 #include "src/core/ext/client_config/lb_policy_registry.h"
 #include "src/core/lib/debug/trace.h"
 #include "src/core/lib/transport/connectivity_state.h"
+#include "src/core/lib/transport/static_metadata.h"
 
 typedef struct round_robin_lb_policy round_robin_lb_policy;
 
@@ -76,15 +77,32 @@
  * Once a pick is available, \a target is updated and \a on_complete called. */
 typedef struct pending_pick {
   struct pending_pick *next;
+
+  /* polling entity for the pick()'s async notification */
   grpc_polling_entity *pollent;
+
+  /* output argument where to store the pick()ed user_data. It'll be NULL if no
+   * such data is present or there's an error (the definite test for errors is
+   * \a target being NULL). */
+  void **user_data;
+
+  /* bitmask passed to pick() and used for selective cancelling. See
+   * grpc_lb_policy_cancel_picks() */
   uint32_t initial_metadata_flags;
+
+  /* output argument where to store the pick()ed connected subchannel, or NULL
+   * upon error. */
   grpc_connected_subchannel **target;
+
+  /* to be invoked once the pick() has completed (regardless of success) */
   grpc_closure *on_complete;
 } pending_pick;
 
 /** List of subchannels in a connectivity READY state */
 typedef struct ready_list {
   grpc_subchannel *subchannel;
+  /* references namesake entry in subchannel_data */
+  void *user_data;
   struct ready_list *next;
   struct ready_list *prev;
 } ready_list;
@@ -102,12 +120,21 @@
   ready_list *ready_list_node;
   /** last observed connectivity */
   grpc_connectivity_state connectivity_state;
+  /** the subchannel's target user data */
+  void *user_data;
 } subchannel_data;
 
 struct round_robin_lb_policy {
   /** base policy: must be first */
   grpc_lb_policy base;
 
+  /** total number of addresses received at creation time */
+  size_t num_addresses;
+  /** array holding the borrowed and opaque pointers to incoming user data, one
+   * per incoming address.  These individual pointers will be returned as-is in
+   * successful picks. */
+  void **user_data_pointers;
+
   /** all our subchannels */
   size_t num_subchannels;
   subchannel_data **subchannels;
@@ -166,16 +193,19 @@
 
   if (grpc_lb_round_robin_trace) {
     gpr_log(GPR_DEBUG, "[READYLIST] ADVANCED LAST PICK. NOW AT NODE %p (SC %p)",
-            p->ready_list_last_pick, p->ready_list_last_pick->subchannel);
+            (void *)p->ready_list_last_pick,
+            (void *)p->ready_list_last_pick->subchannel);
   }
 }
 
 /** Prepends (relative to the root at p->ready_list) the connected subchannel \a
  * csc to the list of ready subchannels. */
 static ready_list *add_connected_sc_locked(round_robin_lb_policy *p,
-                                           grpc_subchannel *sc) {
+                                           subchannel_data *sd) {
   ready_list *new_elem = gpr_malloc(sizeof(ready_list));
-  new_elem->subchannel = sc;
+  memset(new_elem, 0, sizeof(ready_list));
+  new_elem->subchannel = sd->subchannel;
+  new_elem->user_data = sd->user_data;
   if (p->ready_list.prev == NULL) {
     /* first element */
     new_elem->next = &p->ready_list;
@@ -189,7 +219,8 @@
     p->ready_list.prev = new_elem;
   }
   if (grpc_lb_round_robin_trace) {
-    gpr_log(GPR_DEBUG, "[READYLIST] ADDING NODE %p (SC %p)", new_elem, sc);
+    gpr_log(GPR_DEBUG, "[READYLIST] ADDING NODE %p (Conn. SC %p)",
+            (void *)new_elem, (void *)sd->subchannel);
   }
   return new_elem;
 }
@@ -216,8 +247,8 @@
   }
 
   if (grpc_lb_round_robin_trace) {
-    gpr_log(GPR_DEBUG, "[READYLIST] REMOVED NODE %p (SC %p)", node,
-            node->subchannel);
+    gpr_log(GPR_DEBUG, "[READYLIST] REMOVED NODE %p (SC %p)", (void *)node,
+            (void *)node->subchannel);
   }
 
   node->next = NULL;
@@ -229,9 +260,8 @@
 
 static void rr_destroy(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol) {
   round_robin_lb_policy *p = (round_robin_lb_policy *)pol;
-  size_t i;
   ready_list *elem;
-  for (i = 0; i < p->num_subchannels; i++) {
+  for (size_t i = 0; i < p->num_subchannels; i++) {
     subchannel_data *sd = p->subchannels[i];
     GRPC_SUBCHANNEL_UNREF(exec_ctx, sd->subchannel, "round_robin");
     gpr_free(sd);
@@ -251,6 +281,8 @@
     gpr_free(elem);
     elem = tmp;
   }
+
+  gpr_free(p->user_data_pointers);
   gpr_free(p);
 }
 
@@ -337,7 +369,7 @@
   p->started_picking = 1;
 
   if (grpc_lb_round_robin_trace) {
-    gpr_log(GPR_DEBUG, "LB_POLICY: p=%p num_subchannels=%" PRIuPTR, p,
+    gpr_log(GPR_DEBUG, "LB_POLICY: p=%p num_subchannels=%" PRIuPTR, (void *)p,
             p->num_subchannels);
   }
 
@@ -361,38 +393,43 @@
 }
 
 static int rr_pick(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol,
-                   grpc_polling_entity *pollent,
-                   grpc_metadata_batch *initial_metadata,
-                   uint32_t initial_metadata_flags,
-                   grpc_connected_subchannel **target,
+                   const grpc_lb_policy_pick_args *pick_args,
+                   grpc_connected_subchannel **target, void **user_data,
                    grpc_closure *on_complete) {
   round_robin_lb_policy *p = (round_robin_lb_policy *)pol;
   pending_pick *pp;
   ready_list *selected;
   gpr_mu_lock(&p->mu);
   if ((selected = peek_next_connected_locked(p))) {
+    /* readily available, report right away */
     gpr_mu_unlock(&p->mu);
     *target = grpc_subchannel_get_connected_subchannel(selected->subchannel);
+
+    if (user_data != NULL) {
+      *user_data = selected->user_data;
+    }
     if (grpc_lb_round_robin_trace) {
       gpr_log(GPR_DEBUG,
-              "[RR PICK] TARGET <-- CONNECTED SUBCHANNEL %p (NODE %p)", *target,
-              selected);
+              "[RR PICK] TARGET <-- CONNECTED SUBCHANNEL %p (NODE %p)",
+              (void *)*target, (void *)selected);
     }
     /* only advance the last picked pointer if the selection was used */
     advance_last_picked_locked(p);
     return 1;
   } else {
+    /* no pick currently available. Save for later in list of pending picks */
     if (!p->started_picking) {
       start_picking(exec_ctx, p);
     }
-    grpc_polling_entity_add_to_pollset_set(exec_ctx, pollent,
+    grpc_polling_entity_add_to_pollset_set(exec_ctx, pick_args->pollent,
                                            p->base.interested_parties);
     pp = gpr_malloc(sizeof(*pp));
     pp->next = p->pending_picks;
-    pp->pollent = pollent;
+    pp->pollent = pick_args->pollent;
     pp->target = target;
     pp->on_complete = on_complete;
-    pp->initial_metadata_flags = initial_metadata_flags;
+    pp->initial_metadata_flags = pick_args->initial_metadata_flags;
+    pp->user_data = user_data;
     p->pending_picks = pp;
     gpr_mu_unlock(&p->mu);
     return 0;
@@ -421,7 +458,7 @@
                                     "connecting_ready");
         /* add the newly connected subchannel to the list of connected ones.
          * Note that it goes to the "end of the line". */
-        sd->ready_list_node = add_connected_sc_locked(p, sd->subchannel);
+        sd->ready_list_node = add_connected_sc_locked(p, sd);
         /* at this point we know there's at least one suitable subchannel. Go
          * ahead and pick one and notify the pending suitors in
          * p->pending_picks. This preemtively replicates rr_pick()'s actions. */
@@ -433,12 +470,16 @@
         }
         while ((pp = p->pending_picks)) {
           p->pending_picks = pp->next;
+
           *pp->target =
               grpc_subchannel_get_connected_subchannel(selected->subchannel);
+          if (pp->user_data != NULL) {
+            *pp->user_data = selected->user_data;
+          }
           if (grpc_lb_round_robin_trace) {
             gpr_log(GPR_DEBUG,
                     "[RR CONN CHANGED] TARGET <-- SUBCHANNEL %p (NODE %p)",
-                    selected->subchannel, selected);
+                    (void *)selected->subchannel, (void *)selected);
           }
           grpc_polling_entity_del_from_pollset_set(exec_ctx, pp->pollent,
                                                    p->base.interested_parties);
@@ -570,20 +611,25 @@
                                           grpc_lb_policy_args *args) {
   GPR_ASSERT(args->addresses != NULL);
   GPR_ASSERT(args->client_channel_factory != NULL);
+  if (args->num_addresses == 0) return NULL;
 
   round_robin_lb_policy *p = gpr_malloc(sizeof(*p));
   memset(p, 0, sizeof(*p));
 
-  p->subchannels =
-      gpr_malloc(sizeof(*p->subchannels) * args->addresses->naddrs);
-  memset(p->subchannels, 0, sizeof(*p->subchannels) * args->addresses->naddrs);
+  p->num_addresses = args->num_addresses;
+  p->subchannels = gpr_malloc(sizeof(subchannel_data) * p->num_addresses);
+  memset(p->subchannels, 0, sizeof(*p->subchannels) * p->num_addresses);
+  p->user_data_pointers = gpr_malloc(sizeof(void *) * p->num_addresses);
+  memset(p->user_data_pointers, 0, sizeof(void *) * p->num_addresses);
 
   grpc_subchannel_args sc_args;
   size_t subchannel_idx = 0;
-  for (size_t i = 0; i < args->addresses->naddrs; i++) {
+  for (size_t i = 0; i < p->num_addresses; i++) {
     memset(&sc_args, 0, sizeof(grpc_subchannel_args));
-    sc_args.addr = (struct sockaddr *)(args->addresses->addrs[i].addr);
-    sc_args.addr_len = (size_t)args->addresses->addrs[i].len;
+    sc_args.addr = (struct sockaddr *)args->addresses[i].resolved_address->addr;
+    sc_args.addr_len = args->addresses[i].resolved_address->len;
+
+    p->user_data_pointers[i] = args->addresses[i].user_data;
 
     grpc_subchannel *subchannel = grpc_client_channel_factory_create_subchannel(
         exec_ctx, args->client_channel_factory, &sc_args);
@@ -595,12 +641,14 @@
       sd->policy = p;
       sd->index = subchannel_idx;
       sd->subchannel = subchannel;
+      sd->user_data = p->user_data_pointers[i];
       ++subchannel_idx;
       grpc_closure_init(&sd->connectivity_changed_closure,
                         rr_connectivity_changed, sd);
     }
   }
   if (subchannel_idx == 0) {
+    /* couldn't create any subchannel. Bail out */
     gpr_free(p->subchannels);
     gpr_free(p);
     return NULL;
diff --git a/src/core/ext/resolver/dns/native/dns_resolver.c b/src/core/ext/resolver/dns/native/dns_resolver.c
index 79682e7..32e9de6 100644
--- a/src/core/ext/resolver/dns/native/dns_resolver.c
+++ b/src/core/ext/resolver/dns/native/dns_resolver.c
@@ -175,10 +175,18 @@
     grpc_lb_policy_args lb_policy_args;
     result = grpc_resolver_result_create();
     memset(&lb_policy_args, 0, sizeof(lb_policy_args));
-    lb_policy_args.addresses = addresses;
+    lb_policy_args.num_addresses = addresses->naddrs;
+    lb_policy_args.addresses =
+        gpr_malloc(sizeof(grpc_lb_address) * lb_policy_args.num_addresses);
+    memset(lb_policy_args.addresses, 0,
+           sizeof(grpc_lb_address) * lb_policy_args.num_addresses);
+    for (size_t i = 0; i < addresses->naddrs; ++i) {
+      lb_policy_args.addresses[i].resolved_address = &r->addresses->addrs[i];
+    }
     lb_policy_args.client_channel_factory = r->client_channel_factory;
     lb_policy =
         grpc_lb_policy_create(exec_ctx, r->lb_policy_name, &lb_policy_args);
+    gpr_free(lb_policy_args.addresses);
     if (lb_policy != NULL) {
       grpc_resolver_result_set_lb_policy(result, lb_policy);
       GRPC_LB_POLICY_UNREF(exec_ctx, lb_policy, "construction");
diff --git a/src/core/ext/resolver/sockaddr/sockaddr_resolver.c b/src/core/ext/resolver/sockaddr/sockaddr_resolver.c
index 3807522..4252852 100644
--- a/src/core/ext/resolver/sockaddr/sockaddr_resolver.c
+++ b/src/core/ext/resolver/sockaddr/sockaddr_resolver.c
@@ -125,10 +125,18 @@
     grpc_resolver_result *result = grpc_resolver_result_create();
     grpc_lb_policy_args lb_policy_args;
     memset(&lb_policy_args, 0, sizeof(lb_policy_args));
-    lb_policy_args.addresses = r->addresses;
+    lb_policy_args.num_addresses = r->addresses->naddrs;
+    lb_policy_args.addresses =
+        gpr_malloc(sizeof(grpc_lb_address) * lb_policy_args.num_addresses);
+    memset(lb_policy_args.addresses, 0,
+           sizeof(grpc_lb_address) * lb_policy_args.num_addresses);
+    for (size_t i = 0; i < lb_policy_args.num_addresses; ++i) {
+      lb_policy_args.addresses[i].resolved_address = &r->addresses->addrs[i];
+    }
     lb_policy_args.client_channel_factory = r->client_channel_factory;
     grpc_lb_policy *lb_policy =
         grpc_lb_policy_create(exec_ctx, r->lb_policy_name, &lb_policy_args);
+    gpr_free(lb_policy_args.addresses);
     grpc_resolver_result_set_lb_policy(result, lb_policy);
     GRPC_LB_POLICY_UNREF(exec_ctx, lb_policy, "sockaddr");
     r->published = 1;
diff --git a/src/core/ext/transport/chttp2/transport/chttp2_transport.c b/src/core/ext/transport/chttp2/transport/chttp2_transport.c
index 00999e3..53da0e5 100644
--- a/src/core/ext/transport/chttp2/transport/chttp2_transport.c
+++ b/src/core/ext/transport/chttp2/transport/chttp2_transport.c
@@ -89,13 +89,20 @@
 static void writing_action(grpc_exec_ctx *exec_ctx, void *t, grpc_error *error);
 static void reading_action(grpc_exec_ctx *exec_ctx, void *t, grpc_error *error);
 static void parsing_action(grpc_exec_ctx *exec_ctx, void *t, grpc_error *error);
-static void initiate_writing(grpc_exec_ctx *exec_ctx, void *t,
-                             grpc_error *error);
+static void reading_action_locked(grpc_exec_ctx *exec_ctx, void *arg,
+                                  grpc_error *error);
+static void post_parse_locked(grpc_exec_ctx *exec_ctx, void *arg,
+                              grpc_error *error);
+static void initiate_writing_locked(grpc_exec_ctx *exec_ctx, void *t,
+                                    grpc_error *error);
+static void initiate_read_flush_locked(grpc_exec_ctx *exec_ctx, void *t,
+                                       grpc_error *error);
+static void terminate_writing_with_lock(grpc_exec_ctx *exec_ctx, void *t,
+                                        grpc_error *error);
 
 static void start_writing(grpc_exec_ctx *exec_ctx, grpc_chttp2_transport *t);
 static void end_waiting_for_write(grpc_exec_ctx *exec_ctx,
-                                  grpc_chttp2_transport *t, grpc_error *error,
-                                  const char *reason);
+                                  grpc_chttp2_transport *t, grpc_error *error);
 
 /** Set a transport level setting, and push it to our peer */
 static void push_setting(grpc_exec_ctx *exec_ctx, grpc_chttp2_transport *t,
@@ -105,11 +112,6 @@
 static void drop_connection(grpc_exec_ctx *exec_ctx, grpc_chttp2_transport *t,
                             grpc_error *error);
 
-/** Perform a transport_op */
-static void perform_stream_op_locked(grpc_exec_ctx *exec_ctx,
-                                     grpc_chttp2_transport *t,
-                                     grpc_chttp2_stream *s, void *transport_op);
-
 /** Cancel a stream: coming from the transport API */
 static void cancel_from_api(grpc_exec_ctx *exec_ctx,
                             grpc_chttp2_transport_global *transport_global,
@@ -121,22 +123,10 @@
                            grpc_chttp2_stream_global *stream_global,
                            grpc_error *error);
 
-/** Add endpoint from this transport to pollset */
-static void add_to_pollset_locked(grpc_exec_ctx *exec_ctx,
-                                  grpc_chttp2_transport *t,
-                                  grpc_chttp2_stream *s_ignored, void *pollset);
-static void add_to_pollset_set_locked(grpc_exec_ctx *exec_ctx,
-                                      grpc_chttp2_transport *t,
-                                      grpc_chttp2_stream *s_ignored,
-                                      void *pollset_set);
-
 /** Start new streams that have been created if we can */
 static void maybe_start_some_streams(
     grpc_exec_ctx *exec_ctx, grpc_chttp2_transport_global *transport_global);
 
-static void finish_global_actions(grpc_exec_ctx *exec_ctx,
-                                  grpc_chttp2_transport *t);
-
 static void connectivity_state_set(
     grpc_exec_ctx *exec_ctx, grpc_chttp2_transport_global *transport_global,
     grpc_connectivity_state state, grpc_error *error, const char *reason);
@@ -149,14 +139,16 @@
     grpc_chttp2_stream_global *stream_global, size_t max_size_hint,
     size_t have_already);
 static void incoming_byte_stream_destroy_locked(grpc_exec_ctx *exec_ctx,
-                                                grpc_chttp2_transport *t,
-                                                grpc_chttp2_stream *s,
-                                                void *byte_stream);
+                                                void *byte_stream,
+                                                grpc_error *error_ignored);
 static void fail_pending_writes(grpc_exec_ctx *exec_ctx,
                                 grpc_chttp2_transport_global *transport_global,
                                 grpc_chttp2_stream_global *stream_global,
                                 grpc_error *error);
 
+static void set_write_state(grpc_chttp2_transport *t,
+                            grpc_chttp2_write_state state, const char *reason);
+
 /*******************************************************************************
  * CONSTRUCTION/DESTRUCTION/REFCOUNTING
  */
@@ -165,9 +157,7 @@
                                grpc_chttp2_transport *t) {
   size_t i;
 
-  gpr_mu_lock(&t->executor.mu);
-
-  GPR_ASSERT(t->ep == NULL);
+  grpc_endpoint_destroy(exec_ctx, t->ep);
 
   gpr_slice_buffer_destroy(&t->global.qbuf);
 
@@ -191,8 +181,7 @@
   grpc_chttp2_stream_map_destroy(&t->new_stream_map);
   grpc_connectivity_state_destroy(exec_ctx, &t->channel_callback.state_tracker);
 
-  gpr_mu_unlock(&t->executor.mu);
-  gpr_mu_destroy(&t->executor.mu);
+  grpc_combiner_destroy(exec_ctx, t->executor.combiner);
 
   /* callback remaining pings: they're not allowed to call into the transpot,
      and maybe they hold resources that need to be freed */
@@ -250,12 +239,13 @@
   memset(t, 0, sizeof(*t));
 
   t->base.vtable = &vtable;
+  t->executor.write_state = GRPC_CHTTP2_WRITES_CORKED;
   t->ep = ep;
-  /* one ref is for destroy, the other for when ep becomes NULL */
-  gpr_ref_init(&t->refs, 2);
+  /* one ref is for destroy */
+  gpr_ref_init(&t->refs, 1);
   /* ref is dropped at transport close() */
   gpr_ref_init(&t->shutdown_ep_refs, 1);
-  gpr_mu_init(&t->executor.mu);
+  t->executor.combiner = grpc_combiner_create(grpc_endpoint_get_workqueue(ep));
   t->peer_string = grpc_endpoint_get_peer(ep);
   t->endpoint_reading = 1;
   t->global.next_stream_id = is_client ? 1 : 2;
@@ -281,23 +271,22 @@
   grpc_chttp2_hpack_compressor_init(&t->writing.hpack_compressor);
   grpc_closure_init(&t->writing_action, writing_action, t);
   grpc_closure_init(&t->reading_action, reading_action, t);
+  grpc_closure_init(&t->reading_action_locked, reading_action_locked, t);
   grpc_closure_init(&t->parsing_action, parsing_action, t);
-  grpc_closure_init(&t->initiate_writing, initiate_writing, t);
+  grpc_closure_init(&t->post_parse_locked, post_parse_locked, t);
+  grpc_closure_init(&t->initiate_writing, initiate_writing_locked, t);
+  grpc_closure_init(&t->terminate_writing, terminate_writing_with_lock, t);
+  grpc_closure_init(&t->initiate_read_flush_locked, initiate_read_flush_locked,
+                    t);
+  grpc_closure_init(&t->writing.done_cb, grpc_chttp2_terminate_writing,
+                    &t->writing);
 
   gpr_slice_buffer_init(&t->parsing.qbuf);
   grpc_chttp2_goaway_parser_init(&t->parsing.goaway_parser);
   grpc_chttp2_hpack_parser_init(&t->parsing.hpack_parser);
 
-  grpc_closure_init(&t->writing.done_cb, grpc_chttp2_terminate_writing,
-                    &t->writing);
   gpr_slice_buffer_init(&t->read_buffer);
 
-  if (is_client) {
-    gpr_slice_buffer_add(
-        &t->global.qbuf,
-        gpr_slice_from_copied_string(GRPC_CHTTP2_CLIENT_CONNECT_STRING));
-    grpc_chttp2_initiate_write(exec_ctx, &t->global, false, "initial_write");
-  }
   /* 8 is a random stab in the dark as to a good initial size: it's small enough
      that it shouldn't waste memory for infrequently used connections, yet
      large enough that the exponential growth should happen nicely when it's
@@ -320,6 +309,13 @@
   t->global.force_send_settings = 1 << GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE;
   t->global.sent_local_settings = 0;
 
+  if (is_client) {
+    gpr_slice_buffer_add(
+        &t->writing.outbuf,
+        gpr_slice_from_copied_string(GRPC_CHTTP2_CLIENT_CONNECT_STRING));
+    grpc_chttp2_initiate_write(exec_ctx, &t->global, false, "initial_write");
+  }
+
   /* configure http2 the way we like it */
   if (is_client) {
     push_setting(exec_ctx, t, GRPC_CHTTP2_SETTINGS_ENABLE_PUSH, 0);
@@ -424,47 +420,39 @@
       }
     }
   }
+
+  set_write_state(t, GRPC_CHTTP2_WRITING_INACTIVE, "uncork");
+  grpc_chttp2_initiate_write(exec_ctx, &t->global, false, "init");
 }
 
-static void destroy_transport_locked(grpc_exec_ctx *exec_ctx,
-                                     grpc_chttp2_transport *t,
-                                     grpc_chttp2_stream *s_ignored,
-                                     void *arg_ignored) {
+static void destroy_transport_locked(grpc_exec_ctx *exec_ctx, void *tp,
+                                     grpc_error *error) {
+  grpc_chttp2_transport *t = tp;
   t->destroying = 1;
   drop_connection(exec_ctx, t, GRPC_ERROR_CREATE("Transport destroyed"));
+  UNREF_TRANSPORT(exec_ctx, t, "destroy");
 }
 
 static void destroy_transport(grpc_exec_ctx *exec_ctx, grpc_transport *gt) {
   grpc_chttp2_transport *t = (grpc_chttp2_transport *)gt;
-  grpc_chttp2_run_with_global_lock(exec_ctx, t, NULL, destroy_transport_locked,
-                                   NULL, 0);
-  UNREF_TRANSPORT(exec_ctx, t, "destroy");
+  grpc_combiner_execute(exec_ctx, t->executor.combiner,
+                        grpc_closure_create(destroy_transport_locked, t),
+                        GRPC_ERROR_NONE);
 }
 
 /** block grpc_endpoint_shutdown being called until a paired
     allow_endpoint_shutdown is made */
 static void prevent_endpoint_shutdown(grpc_chttp2_transport *t) {
-  GPR_ASSERT(t->ep);
   gpr_ref(&t->shutdown_ep_refs);
 }
 
 static void allow_endpoint_shutdown_locked(grpc_exec_ctx *exec_ctx,
                                            grpc_chttp2_transport *t) {
   if (gpr_unref(&t->shutdown_ep_refs)) {
-    if (t->ep) {
-      grpc_endpoint_shutdown(exec_ctx, t->ep);
-    }
+    grpc_endpoint_shutdown(exec_ctx, t->ep);
   }
 }
 
-static void destroy_endpoint(grpc_exec_ctx *exec_ctx,
-                             grpc_chttp2_transport *t) {
-  grpc_endpoint_destroy(exec_ctx, t->ep);
-  t->ep = NULL;
-  /* safe because we'll still have the ref for write */
-  UNREF_TRANSPORT(exec_ctx, t, "disconnect");
-}
-
 static void close_transport_locked(grpc_exec_ctx *exec_ctx,
                                    grpc_chttp2_transport *t,
                                    grpc_error *error) {
@@ -475,9 +463,7 @@
     t->closed = 1;
     connectivity_state_set(exec_ctx, &t->global, GRPC_CHANNEL_SHUTDOWN,
                            GRPC_ERROR_REF(error), "close_transport");
-    if (t->ep) {
-      allow_endpoint_shutdown_locked(exec_ctx, t);
-    }
+    allow_endpoint_shutdown_locked(exec_ctx, t);
 
     /* flush writable stream list to avoid dangling references */
     grpc_chttp2_stream_global *stream_global;
@@ -511,21 +497,23 @@
 }
 #endif
 
-static void finish_init_stream_locked(grpc_exec_ctx *exec_ctx,
-                                      grpc_chttp2_transport *t,
-                                      grpc_chttp2_stream *s,
-                                      void *arg_ignored) {
-  grpc_chttp2_register_stream(t, s);
+static void finish_init_stream_locked(grpc_exec_ctx *exec_ctx, void *sp,
+                                      grpc_error *error) {
+  grpc_chttp2_stream *s = sp;
+  grpc_chttp2_register_stream(s->t, s);
+  GRPC_CHTTP2_STREAM_UNREF(exec_ctx, &s->global, "init");
 }
 
 static int init_stream(grpc_exec_ctx *exec_ctx, grpc_transport *gt,
                        grpc_stream *gs, grpc_stream_refcount *refcount,
                        const void *server_data) {
+  GPR_TIMER_BEGIN("init_stream", 0);
   grpc_chttp2_transport *t = (grpc_chttp2_transport *)gt;
   grpc_chttp2_stream *s = (grpc_chttp2_stream *)gs;
 
   memset(s, 0, sizeof(*s));
 
+  s->t = t;
   s->refcount = refcount;
   /* We reserve one 'active stream' that's dropped when the stream is
      read-closed. The others are for incoming_byte_streams that are actively
@@ -560,16 +548,21 @@
     s->global.in_stream_map = true;
   }
 
-  grpc_chttp2_run_with_global_lock(exec_ctx, t, s, finish_init_stream_locked,
-                                   NULL, 0);
+  grpc_closure_init(&s->init_stream, finish_init_stream_locked, s);
+  GRPC_CHTTP2_STREAM_REF(&s->global, "init");
+  grpc_combiner_execute(exec_ctx, t->executor.combiner, &s->init_stream,
+                        GRPC_ERROR_NONE);
+
+  GPR_TIMER_END("init_stream", 0);
 
   return 0;
 }
 
-static void destroy_stream_locked(grpc_exec_ctx *exec_ctx,
-                                  grpc_chttp2_transport *t,
-                                  grpc_chttp2_stream *s, void *arg) {
+static void destroy_stream_locked(grpc_exec_ctx *exec_ctx, void *sp,
+                                  grpc_error *error) {
   grpc_byte_stream *bs;
+  grpc_chttp2_stream *s = sp;
+  grpc_chttp2_transport *t = s->t;
 
   GPR_TIMER_BEGIN("destroy_stream", 0);
 
@@ -588,7 +581,7 @@
 
   while (
       (bs = grpc_chttp2_incoming_frame_queue_pop(&s->global.incoming_frames))) {
-    incoming_byte_stream_destroy_locked(exec_ctx, NULL, NULL, bs);
+    incoming_byte_stream_destroy_locked(exec_ctx, bs, GRPC_ERROR_NONE);
   }
 
   grpc_chttp2_list_remove_unannounced_incoming_window_available(&t->global,
@@ -625,16 +618,20 @@
 
   GPR_TIMER_END("destroy_stream", 0);
 
-  gpr_free(arg);
+  gpr_free(s->destroy_stream_arg);
 }
 
 static void destroy_stream(grpc_exec_ctx *exec_ctx, grpc_transport *gt,
                            grpc_stream *gs, void *and_free_memory) {
+  GPR_TIMER_BEGIN("destroy_stream", 0);
   grpc_chttp2_transport *t = (grpc_chttp2_transport *)gt;
   grpc_chttp2_stream *s = (grpc_chttp2_stream *)gs;
 
-  grpc_chttp2_run_with_global_lock(exec_ctx, t, s, destroy_stream_locked,
-                                   and_free_memory, 0);
+  s->destroy_stream_arg = and_free_memory;
+  grpc_closure_init(&s->destroy_stream, destroy_stream_locked, s);
+  grpc_combiner_execute(exec_ctx, t->executor.combiner, &s->destroy_stream,
+                        GRPC_ERROR_NONE);
+  GPR_TIMER_END("destroy_stream", 0);
 }
 
 grpc_chttp2_stream_parsing *grpc_chttp2_parsing_lookup_stream(
@@ -665,12 +662,10 @@
 
 static const char *write_state_name(grpc_chttp2_write_state state) {
   switch (state) {
+    case GRPC_CHTTP2_WRITES_CORKED:
+      return "CORKED";
     case GRPC_CHTTP2_WRITING_INACTIVE:
       return "INACTIVE";
-    case GRPC_CHTTP2_WRITE_REQUESTED_NO_POLLER:
-      return "REQUESTED[p=0]";
-    case GRPC_CHTTP2_WRITE_REQUESTED_WITH_POLLER:
-      return "REQUESTED[p=1]";
     case GRPC_CHTTP2_WRITE_SCHEDULED:
       return "SCHEDULED";
     case GRPC_CHTTP2_WRITING:
@@ -693,120 +688,18 @@
   t->executor.write_state = state;
 }
 
-static void finish_global_actions(grpc_exec_ctx *exec_ctx,
-                                  grpc_chttp2_transport *t) {
-  grpc_chttp2_executor_action_header *hdr;
-  grpc_chttp2_executor_action_header *next;
-
-  GPR_TIMER_BEGIN("finish_global_actions", 0);
-
-  for (;;) {
-    check_read_ops(exec_ctx, &t->global);
-
-    gpr_mu_lock(&t->executor.mu);
-    if (t->executor.pending_actions_head != NULL) {
-      hdr = t->executor.pending_actions_head;
-      t->executor.pending_actions_head = t->executor.pending_actions_tail =
-          NULL;
-      gpr_mu_unlock(&t->executor.mu);
-      while (hdr != NULL) {
-        GPR_TIMER_BEGIN("chttp2:locked_action", 0);
-        hdr->action(exec_ctx, t, hdr->stream, hdr->arg);
-        GPR_TIMER_END("chttp2:locked_action", 0);
-        next = hdr->next;
-        gpr_free(hdr);
-        UNREF_TRANSPORT(exec_ctx, t, "pending_action");
-        hdr = next;
-      }
-      continue;
-    } else {
-      t->executor.global_active = false;
-      switch (t->executor.write_state) {
-        case GRPC_CHTTP2_WRITE_REQUESTED_WITH_POLLER:
-          set_write_state(t, GRPC_CHTTP2_WRITE_SCHEDULED, "unlocking");
-          REF_TRANSPORT(t, "initiate_writing");
-          gpr_mu_unlock(&t->executor.mu);
-          grpc_exec_ctx_sched(
-              exec_ctx, &t->initiate_writing, GRPC_ERROR_NONE,
-              t->ep != NULL ? grpc_endpoint_get_workqueue(t->ep) : NULL);
-          break;
-        case GRPC_CHTTP2_WRITE_REQUESTED_NO_POLLER:
-          start_writing(exec_ctx, t);
-          gpr_mu_unlock(&t->executor.mu);
-          break;
-        case GRPC_CHTTP2_WRITING_INACTIVE:
-        case GRPC_CHTTP2_WRITING:
-        case GRPC_CHTTP2_WRITING_STALE_WITH_POLLER:
-        case GRPC_CHTTP2_WRITING_STALE_NO_POLLER:
-        case GRPC_CHTTP2_WRITE_SCHEDULED:
-          gpr_mu_unlock(&t->executor.mu);
-          break;
-      }
-    }
-    break;
-  }
-
-  GPR_TIMER_END("finish_global_actions", 0);
+static void initiate_writing_locked(grpc_exec_ctx *exec_ctx, void *tp,
+                                    grpc_error *error) {
+  grpc_chttp2_transport *t = tp;
+  GPR_ASSERT(t->executor.write_state == GRPC_CHTTP2_WRITE_SCHEDULED);
+  start_writing(exec_ctx, t);
 }
 
-void grpc_chttp2_run_with_global_lock(grpc_exec_ctx *exec_ctx,
-                                      grpc_chttp2_transport *t,
-                                      grpc_chttp2_stream *optional_stream,
-                                      grpc_chttp2_locked_action action,
-                                      void *arg, size_t sizeof_arg) {
-  grpc_chttp2_executor_action_header *hdr;
-
-  GPR_TIMER_BEGIN("grpc_chttp2_run_with_global_lock", 0);
-
-  REF_TRANSPORT(t, "run_global");
-  gpr_mu_lock(&t->executor.mu);
-
-  for (;;) {
-    if (!t->executor.global_active) {
-      t->executor.global_active = 1;
-      gpr_mu_unlock(&t->executor.mu);
-
-      GPR_TIMER_BEGIN("chttp2:locked_action", 0);
-      action(exec_ctx, t, optional_stream, arg);
-      GPR_TIMER_END("chttp2:locked_action", 0);
-
-      finish_global_actions(exec_ctx, t);
-    } else {
-      gpr_mu_unlock(&t->executor.mu);
-
-      hdr = gpr_malloc(sizeof(*hdr) + sizeof_arg);
-      hdr->stream = optional_stream;
-      hdr->action = action;
-      if (sizeof_arg == 0) {
-        hdr->arg = arg;
-      } else {
-        hdr->arg = hdr + 1;
-        memcpy(hdr->arg, arg, sizeof_arg);
-      }
-
-      gpr_mu_lock(&t->executor.mu);
-      if (!t->executor.global_active) {
-        /* global lock was released while allocating memory: release & retry */
-        gpr_free(hdr);
-        continue;
-      }
-      hdr->next = NULL;
-      if (t->executor.pending_actions_head != NULL) {
-        t->executor.pending_actions_tail =
-            t->executor.pending_actions_tail->next = hdr;
-      } else {
-        t->executor.pending_actions_tail = t->executor.pending_actions_head =
-            hdr;
-      }
-      REF_TRANSPORT(t, "pending_action");
-      gpr_mu_unlock(&t->executor.mu);
-    }
-    break;
-  }
-
-  UNREF_TRANSPORT(exec_ctx, t, "run_global");
-
-  GPR_TIMER_END("grpc_chttp2_run_with_global_lock", 0);
+static void initiate_read_flush_locked(grpc_exec_ctx *exec_ctx, void *tp,
+                                       grpc_error *error) {
+  grpc_chttp2_transport *t = tp;
+  t->executor.check_read_ops_scheduled = false;
+  check_read_ops(exec_ctx, &t->global);
 }
 
 /*******************************************************************************
@@ -816,11 +709,12 @@
 void grpc_chttp2_initiate_write(grpc_exec_ctx *exec_ctx,
                                 grpc_chttp2_transport_global *transport_global,
                                 bool covered_by_poller, const char *reason) {
+  GPR_TIMER_BEGIN("grpc_chttp2_initiate_write", 0);
+
   /* Perform state checks, and transition to a scheduled state if appropriate.
-     Each time we finish the global lock execution, we check if we need to
-     write. If we do:
-      - (if there is a poller surrounding the write) schedule
-        initiate_writing, which locks and calls initiate_writing_locked to...
+     If we are inactive, schedule a write chain to begin once the transport
+     combiner finishes any executions in its current batch (which may be
+     scheduled AFTER this code executes). The write chain will:
       - call start_writing, which verifies (under the global lock) that there
         are things that need to be written by calling
         grpc_chttp2_unlocking_check_writes, and if so schedules writing_action
@@ -830,30 +724,27 @@
         to do *another* write immediately, and if so loops back to
         start_writing.
 
-      Current problems:
+     Current problems:
        - too much lock entry/exiting
        - the writing thread can become stuck indefinitely (punt through the
          workqueue periodically to fix) */
 
   grpc_chttp2_transport *t = TRANSPORT_FROM_GLOBAL(transport_global);
   switch (t->executor.write_state) {
+    case GRPC_CHTTP2_WRITES_CORKED:
+      break;
     case GRPC_CHTTP2_WRITING_INACTIVE:
-      set_write_state(t, covered_by_poller
-                             ? GRPC_CHTTP2_WRITE_REQUESTED_WITH_POLLER
-                             : GRPC_CHTTP2_WRITE_REQUESTED_NO_POLLER,
-                      reason);
-      break;
-    case GRPC_CHTTP2_WRITE_REQUESTED_WITH_POLLER:
-      /* nothing to do: write already requested */
-      break;
-    case GRPC_CHTTP2_WRITE_REQUESTED_NO_POLLER:
-      if (covered_by_poller) {
-        /* upgrade to note poller is available to cover the write */
-        set_write_state(t, GRPC_CHTTP2_WRITE_REQUESTED_WITH_POLLER, reason);
-      }
+      set_write_state(t, GRPC_CHTTP2_WRITE_SCHEDULED, reason);
+      REF_TRANSPORT(t, "writing");
+      grpc_combiner_execute_finally(exec_ctx, t->executor.combiner,
+                                    &t->initiate_writing, GRPC_ERROR_NONE,
+                                    covered_by_poller);
       break;
     case GRPC_CHTTP2_WRITE_SCHEDULED:
-      /* nothing to do: write already scheduled */
+      if (covered_by_poller) {
+        /* upgrade to note poller is available to cover the write */
+        grpc_combiner_force_async_finally(t->executor.combiner);
+      }
       break;
     case GRPC_CHTTP2_WRITING:
       set_write_state(t,
@@ -871,15 +762,15 @@
       }
       break;
   }
+  GPR_TIMER_END("grpc_chttp2_initiate_write", 0);
 }
 
 static void start_writing(grpc_exec_ctx *exec_ctx, grpc_chttp2_transport *t) {
-  GPR_ASSERT(t->executor.write_state == GRPC_CHTTP2_WRITE_SCHEDULED ||
-             t->executor.write_state == GRPC_CHTTP2_WRITE_REQUESTED_NO_POLLER);
+  GPR_TIMER_BEGIN("start_writing", 0);
+  GPR_ASSERT(t->executor.write_state == GRPC_CHTTP2_WRITE_SCHEDULED);
   if (!t->closed &&
       grpc_chttp2_unlocking_check_writes(exec_ctx, &t->global, &t->writing)) {
     set_write_state(t, GRPC_CHTTP2_WRITING, "start_writing");
-    REF_TRANSPORT(t, "writing");
     prevent_endpoint_shutdown(t);
     grpc_exec_ctx_sched(exec_ctx, &t->writing_action, GRPC_ERROR_NONE, NULL);
   } else {
@@ -890,25 +781,10 @@
       set_write_state(t, GRPC_CHTTP2_WRITING_INACTIVE,
                       "start_writing:nothing_to_write");
     }
-    end_waiting_for_write(exec_ctx, t, GRPC_ERROR_NONE, "Nothing to write");
-    if (t->ep && !t->endpoint_reading) {
-      destroy_endpoint(exec_ctx, t);
-    }
+    end_waiting_for_write(exec_ctx, t, GRPC_ERROR_NONE);
+    UNREF_TRANSPORT(exec_ctx, t, "writing");
   }
-}
-
-static void initiate_writing_locked(grpc_exec_ctx *exec_ctx,
-                                    grpc_chttp2_transport *t,
-                                    grpc_chttp2_stream *s_unused,
-                                    void *arg_ignored) {
-  start_writing(exec_ctx, t);
-  UNREF_TRANSPORT(exec_ctx, t, "initiate_writing");
-}
-
-static void initiate_writing(grpc_exec_ctx *exec_ctx, void *arg,
-                             grpc_error *error) {
-  grpc_chttp2_run_with_global_lock(exec_ctx, arg, NULL, initiate_writing_locked,
-                                   NULL, 0);
+  GPR_TIMER_END("start_writing", 0);
 }
 
 void grpc_chttp2_become_writable(grpc_exec_ctx *exec_ctx,
@@ -942,15 +818,10 @@
 /* error may be GRPC_ERROR_NONE if there is no error allocated yet.
    In that case, use "reason" as the text for a new error. */
 static void end_waiting_for_write(grpc_exec_ctx *exec_ctx,
-                                  grpc_chttp2_transport *t, grpc_error *error,
-                                  const char *reason) {
+                                  grpc_chttp2_transport *t, grpc_error *error) {
   grpc_chttp2_stream_global *stream_global;
   while (grpc_chttp2_list_pop_closed_waiting_for_writing(&t->global,
                                                          &stream_global)) {
-    if (error == GRPC_ERROR_NONE && reason != NULL) {
-      /* create error object. */
-      error = GRPC_ERROR_CREATE(reason);
-    }
     fail_pending_writes(exec_ctx, &t->global, stream_global,
                         GRPC_ERROR_REF(error));
     GRPC_CHTTP2_STREAM_UNREF(exec_ctx, stream_global, "finish_writes");
@@ -958,12 +829,10 @@
   GRPC_ERROR_UNREF(error);
 }
 
-static void terminate_writing_with_lock(grpc_exec_ctx *exec_ctx,
-                                        grpc_chttp2_transport *t,
-                                        grpc_chttp2_stream *s_ignored,
-                                        void *a) {
-  grpc_error *error = a;
-
+static void terminate_writing_with_lock(grpc_exec_ctx *exec_ctx, void *tp,
+                                        grpc_error *error) {
+  GPR_TIMER_BEGIN("terminate_writing_with_lock", 0);
+  grpc_chttp2_transport *t = tp;
   allow_endpoint_shutdown_locked(exec_ctx, t);
 
   if (error != GRPC_ERROR_NONE) {
@@ -972,39 +841,46 @@
 
   grpc_chttp2_cleanup_writing(exec_ctx, &t->global, &t->writing);
 
-  end_waiting_for_write(exec_ctx, t, error, NULL);
+  end_waiting_for_write(exec_ctx, t, GRPC_ERROR_REF(error));
 
   switch (t->executor.write_state) {
+    case GRPC_CHTTP2_WRITES_CORKED:
     case GRPC_CHTTP2_WRITING_INACTIVE:
-    case GRPC_CHTTP2_WRITE_REQUESTED_WITH_POLLER:
-    case GRPC_CHTTP2_WRITE_REQUESTED_NO_POLLER:
     case GRPC_CHTTP2_WRITE_SCHEDULED:
       GPR_UNREACHABLE_CODE(break);
     case GRPC_CHTTP2_WRITING:
+      GPR_TIMER_MARK("state=writing", 0);
       set_write_state(t, GRPC_CHTTP2_WRITING_INACTIVE, "terminate_writing");
       break;
     case GRPC_CHTTP2_WRITING_STALE_WITH_POLLER:
-      set_write_state(t, GRPC_CHTTP2_WRITE_REQUESTED_WITH_POLLER,
-                      "terminate_writing");
+      GPR_TIMER_MARK("state=writing_stale_with_poller", 0);
+      set_write_state(t, GRPC_CHTTP2_WRITE_SCHEDULED, "terminate_writing");
+      REF_TRANSPORT(t, "writing");
+      grpc_combiner_execute_finally(exec_ctx, t->executor.combiner,
+                                    &t->initiate_writing, GRPC_ERROR_NONE,
+                                    true);
       break;
     case GRPC_CHTTP2_WRITING_STALE_NO_POLLER:
-      set_write_state(t, GRPC_CHTTP2_WRITE_REQUESTED_NO_POLLER,
-                      "terminate_writing");
+      GPR_TIMER_MARK("state=writing_stale_no_poller", 0);
+      set_write_state(t, GRPC_CHTTP2_WRITE_SCHEDULED, "terminate_writing");
+      REF_TRANSPORT(t, "writing");
+      grpc_combiner_execute_finally(exec_ctx, t->executor.combiner,
+                                    &t->initiate_writing, GRPC_ERROR_NONE,
+                                    false);
       break;
   }
 
-  if (t->ep && !t->endpoint_reading) {
-    destroy_endpoint(exec_ctx, t);
-  }
-
   UNREF_TRANSPORT(exec_ctx, t, "writing");
+  GPR_TIMER_END("terminate_writing_with_lock", 0);
 }
 
 void grpc_chttp2_terminate_writing(grpc_exec_ctx *exec_ctx,
                                    void *transport_writing, grpc_error *error) {
+  GPR_TIMER_BEGIN("grpc_chttp2_terminate_writing", 0);
   grpc_chttp2_transport *t = TRANSPORT_FROM_WRITING(transport_writing);
-  grpc_chttp2_run_with_global_lock(
-      exec_ctx, t, NULL, terminate_writing_with_lock, GRPC_ERROR_REF(error), 0);
+  grpc_combiner_execute(exec_ctx, t->executor.combiner, &t->terminate_writing,
+                        GRPC_ERROR_REF(error));
+  GPR_TIMER_END("grpc_chttp2_terminate_writing", 0);
 }
 
 static void writing_action(grpc_exec_ctx *exec_ctx, void *gt,
@@ -1148,15 +1024,22 @@
 
 static void do_nothing(grpc_exec_ctx *exec_ctx, void *arg, grpc_error *error) {}
 
-static void perform_stream_op_locked(grpc_exec_ctx *exec_ctx,
-                                     grpc_chttp2_transport *t,
-                                     grpc_chttp2_stream *s, void *stream_op) {
+static void perform_stream_op_locked(grpc_exec_ctx *exec_ctx, void *stream_op,
+                                     grpc_error *error_ignored) {
   GPR_TIMER_BEGIN("perform_stream_op_locked", 0);
 
   grpc_transport_stream_op *op = stream_op;
+  grpc_chttp2_transport *t = op->transport_private.args[0];
+  grpc_chttp2_stream *s = op->transport_private.args[1];
   grpc_chttp2_transport_global *transport_global = &t->global;
   grpc_chttp2_stream_global *stream_global = &s->global;
 
+  if (grpc_http_trace) {
+    char *str = grpc_transport_stream_op_string(op);
+    gpr_log(GPR_DEBUG, "perform_stream_op_locked: %s", str);
+    gpr_free(str);
+  }
+
   grpc_closure *on_complete = op->on_complete;
   if (on_complete == NULL) {
     on_complete = grpc_closure_create(do_nothing, NULL);
@@ -1211,7 +1094,8 @@
     } else {
       if (contains_non_ok_status(transport_global, op->send_initial_metadata)) {
         stream_global->seen_error = true;
-        grpc_chttp2_list_add_check_read_ops(transport_global, stream_global);
+        grpc_chttp2_list_add_check_read_ops(exec_ctx, transport_global,
+                                            stream_global);
       }
       if (!stream_global->write_closed) {
         if (transport_global->is_client) {
@@ -1278,7 +1162,8 @@
       if (contains_non_ok_status(transport_global,
                                  op->send_trailing_metadata)) {
         stream_global->seen_error = true;
-        grpc_chttp2_list_add_check_read_ops(transport_global, stream_global);
+        grpc_chttp2_list_add_check_read_ops(exec_ctx, transport_global,
+                                            stream_global);
       }
       if (stream_global->write_closed) {
         stream_global->send_trailing_metadata = NULL;
@@ -1303,7 +1188,8 @@
     stream_global->recv_initial_metadata_ready =
         op->recv_initial_metadata_ready;
     stream_global->recv_initial_metadata = op->recv_initial_metadata;
-    grpc_chttp2_list_add_check_read_ops(transport_global, stream_global);
+    grpc_chttp2_list_add_check_read_ops(exec_ctx, transport_global,
+                                        stream_global);
   }
 
   if (op->recv_message != NULL) {
@@ -1317,7 +1203,8 @@
           exec_ctx, transport_global, stream_global,
           transport_global->stream_lookahead, 0);
     }
-    grpc_chttp2_list_add_check_read_ops(transport_global, stream_global);
+    grpc_chttp2_list_add_check_read_ops(exec_ctx, transport_global,
+                                        stream_global);
   }
 
   if (op->recv_trailing_metadata != NULL) {
@@ -1326,21 +1213,30 @@
         add_closure_barrier(on_complete);
     stream_global->recv_trailing_metadata = op->recv_trailing_metadata;
     stream_global->final_metadata_requested = true;
-    grpc_chttp2_list_add_check_read_ops(transport_global, stream_global);
+    grpc_chttp2_list_add_check_read_ops(exec_ctx, transport_global,
+                                        stream_global);
   }
 
   grpc_chttp2_complete_closure_step(exec_ctx, transport_global, stream_global,
                                     &on_complete, GRPC_ERROR_NONE);
 
   GPR_TIMER_END("perform_stream_op_locked", 0);
+  GRPC_CHTTP2_STREAM_UNREF(exec_ctx, &s->global, "perform_stream_op");
 }
 
 static void perform_stream_op(grpc_exec_ctx *exec_ctx, grpc_transport *gt,
                               grpc_stream *gs, grpc_transport_stream_op *op) {
+  GPR_TIMER_BEGIN("perform_stream_op", 0);
   grpc_chttp2_transport *t = (grpc_chttp2_transport *)gt;
   grpc_chttp2_stream *s = (grpc_chttp2_stream *)gs;
-  grpc_chttp2_run_with_global_lock(exec_ctx, t, s, perform_stream_op_locked, op,
-                                   sizeof(*op));
+  grpc_closure_init(&op->transport_private.closure, perform_stream_op_locked,
+                    op);
+  op->transport_private.args[0] = gt;
+  op->transport_private.args[1] = gs;
+  GRPC_CHTTP2_STREAM_REF(&s->global, "perform_stream_op");
+  grpc_combiner_execute(exec_ctx, t->executor.combiner,
+                        &op->transport_private.closure, GRPC_ERROR_NONE);
+  GPR_TIMER_END("perform_stream_op", 0);
 }
 
 static void send_ping_locked(grpc_exec_ctx *exec_ctx, grpc_chttp2_transport *t,
@@ -1362,13 +1258,20 @@
   grpc_chttp2_initiate_write(exec_ctx, &t->global, true, "send_ping");
 }
 
-static void ack_ping_locked(grpc_exec_ctx *exec_ctx, grpc_chttp2_transport *t,
-                            grpc_chttp2_stream *s, void *opaque_8bytes) {
+typedef struct ack_ping_args {
+  grpc_closure closure;
+  grpc_chttp2_transport *t;
+  uint8_t opaque_8bytes[8];
+} ack_ping_args;
+
+static void ack_ping_locked(grpc_exec_ctx *exec_ctx, void *a,
+                            grpc_error *error_ignored) {
+  ack_ping_args *args = a;
   grpc_chttp2_outstanding_ping *ping;
-  grpc_chttp2_transport_global *transport_global = &t->global;
+  grpc_chttp2_transport_global *transport_global = &args->t->global;
   for (ping = transport_global->pings.next; ping != &transport_global->pings;
        ping = ping->next) {
-    if (0 == memcmp(opaque_8bytes, ping->id, 8)) {
+    if (0 == memcmp(args->opaque_8bytes, ping->id, 8)) {
       grpc_exec_ctx_sched(exec_ctx, ping->on_recv, GRPC_ERROR_NONE, NULL);
       ping->next->prev = ping->prev;
       ping->prev->next = ping->next;
@@ -1376,21 +1279,27 @@
       break;
     }
   }
+  UNREF_TRANSPORT(exec_ctx, args->t, "ack_ping");
+  gpr_free(args);
 }
 
 void grpc_chttp2_ack_ping(grpc_exec_ctx *exec_ctx,
                           grpc_chttp2_transport_parsing *transport_parsing,
                           const uint8_t *opaque_8bytes) {
-  grpc_chttp2_run_with_global_lock(
-      exec_ctx, TRANSPORT_FROM_PARSING(transport_parsing), NULL,
-      ack_ping_locked, (void *)opaque_8bytes, 8);
+  ack_ping_args *args = gpr_malloc(sizeof(*args));
+  args->t = TRANSPORT_FROM_PARSING(transport_parsing);
+  memcpy(args->opaque_8bytes, opaque_8bytes, sizeof(args->opaque_8bytes));
+  grpc_closure_init(&args->closure, ack_ping_locked, args);
+  REF_TRANSPORT(args->t, "ack_ping");
+  grpc_combiner_execute(exec_ctx, args->t->executor.combiner, &args->closure,
+                        GRPC_ERROR_NONE);
 }
 
 static void perform_transport_op_locked(grpc_exec_ctx *exec_ctx,
-                                        grpc_chttp2_transport *t,
-                                        grpc_chttp2_stream *s_unused,
-                                        void *stream_op) {
+                                        void *stream_op,
+                                        grpc_error *error_ignored) {
   grpc_transport_op *op = stream_op;
+  grpc_chttp2_transport *t = op->transport_private.args[0];
   grpc_error *close_transport = op->disconnect_with_error;
 
   /* If there's a set_accept_stream ensure that we're not parsing
@@ -1402,8 +1311,6 @@
     return;
   }
 
-  grpc_exec_ctx_sched(exec_ctx, op->on_consumed, GRPC_ERROR_NONE, NULL);
-
   if (op->on_connectivity_state_change != NULL) {
     grpc_connectivity_state_notify_on_state_change(
         exec_ctx, &t->channel_callback.state_tracker, op->connectivity_state,
@@ -1429,11 +1336,11 @@
   }
 
   if (op->bind_pollset) {
-    add_to_pollset_locked(exec_ctx, t, NULL, op->bind_pollset);
+    grpc_endpoint_add_to_pollset(exec_ctx, t->ep, op->bind_pollset);
   }
 
   if (op->bind_pollset_set) {
-    add_to_pollset_set_locked(exec_ctx, t, NULL, op->bind_pollset_set);
+    grpc_endpoint_add_to_pollset_set(exec_ctx, t->ep, op->bind_pollset_set);
   }
 
   if (op->send_ping) {
@@ -1443,13 +1350,21 @@
   if (close_transport != GRPC_ERROR_NONE) {
     close_transport_locked(exec_ctx, t, close_transport);
   }
+
+  grpc_exec_ctx_sched(exec_ctx, op->on_consumed, GRPC_ERROR_NONE, NULL);
+
+  UNREF_TRANSPORT(exec_ctx, t, "transport_op");
 }
 
 static void perform_transport_op(grpc_exec_ctx *exec_ctx, grpc_transport *gt,
                                  grpc_transport_op *op) {
   grpc_chttp2_transport *t = (grpc_chttp2_transport *)gt;
-  grpc_chttp2_run_with_global_lock(
-      exec_ctx, t, NULL, perform_transport_op_locked, op, sizeof(*op));
+  op->transport_private.args[0] = gt;
+  grpc_closure_init(&op->transport_private.closure, perform_transport_op_locked,
+                    op);
+  REF_TRANSPORT(t, "transport_op");
+  grpc_combiner_execute(exec_ctx, t->executor.combiner,
+                        &op->transport_private.closure, GRPC_ERROR_NONE);
 }
 
 /*******************************************************************************
@@ -1458,6 +1373,7 @@
 
 static void check_read_ops(grpc_exec_ctx *exec_ctx,
                            grpc_chttp2_transport_global *transport_global) {
+  GPR_TIMER_BEGIN("check_read_ops", 0);
   grpc_chttp2_stream_global *stream_global;
   grpc_byte_stream *bs;
   while (
@@ -1467,7 +1383,7 @@
       if (stream_global->seen_error) {
         while ((bs = grpc_chttp2_incoming_frame_queue_pop(
                     &stream_global->incoming_frames)) != NULL) {
-          incoming_byte_stream_destroy_locked(exec_ctx, NULL, NULL, bs);
+          incoming_byte_stream_destroy_locked(exec_ctx, bs, GRPC_ERROR_NONE);
         }
         if (stream_global->exceeded_metadata_size) {
           cancel_from_api(
@@ -1490,7 +1406,7 @@
              stream_global->seen_error &&
              (bs = grpc_chttp2_incoming_frame_queue_pop(
                   &stream_global->incoming_frames)) != NULL) {
-        incoming_byte_stream_destroy_locked(exec_ctx, NULL, NULL, bs);
+        incoming_byte_stream_destroy_locked(exec_ctx, bs, GRPC_ERROR_NONE);
       }
       if (stream_global->incoming_frames.head != NULL) {
         *stream_global->recv_message = grpc_chttp2_incoming_frame_queue_pop(
@@ -1511,7 +1427,7 @@
       if (stream_global->seen_error) {
         while ((bs = grpc_chttp2_incoming_frame_queue_pop(
                     &stream_global->incoming_frames)) != NULL) {
-          incoming_byte_stream_destroy_locked(exec_ctx, NULL, NULL, bs);
+          incoming_byte_stream_destroy_locked(exec_ctx, bs, GRPC_ERROR_NONE);
         }
         if (stream_global->exceeded_metadata_size) {
           cancel_from_api(
@@ -1532,6 +1448,7 @@
       }
     }
   }
+  GPR_TIMER_END("check_read_ops", 0);
 }
 
 static void decrement_active_streams_locked(
@@ -1539,7 +1456,8 @@
     grpc_chttp2_stream_global *stream_global) {
   if ((stream_global->all_incoming_byte_streams_finished =
            gpr_unref(&stream_global->active_streams))) {
-    grpc_chttp2_list_add_check_read_ops(transport_global, stream_global);
+    grpc_chttp2_list_add_check_read_ops(exec_ctx, transport_global,
+                                        stream_global);
   }
 }
 
@@ -1643,7 +1561,8 @@
   }
   if (due_to_error != GRPC_ERROR_NONE && !stream_global->seen_error) {
     stream_global->seen_error = true;
-    grpc_chttp2_list_add_check_read_ops(transport_global, stream_global);
+    grpc_chttp2_list_add_check_read_ops(exec_ctx, transport_global,
+                                        stream_global);
   }
   grpc_chttp2_mark_stream_closed(exec_ctx, transport_global, stream_global, 1,
                                  1, due_to_error);
@@ -1655,7 +1574,8 @@
                              grpc_status_code status, gpr_slice *slice) {
   if (status != GRPC_STATUS_OK) {
     stream_global->seen_error = true;
-    grpc_chttp2_list_add_check_read_ops(transport_global, stream_global);
+    grpc_chttp2_list_add_check_read_ops(exec_ctx, transport_global,
+                                        stream_global);
   }
   /* stream_global->recv_trailing_metadata_finished gives us a
      last chance replacement: we've received trailing metadata,
@@ -1679,7 +1599,8 @@
               grpc_mdstr_from_slice(gpr_slice_ref(*slice))));
     }
     stream_global->published_trailing_metadata = true;
-    grpc_chttp2_list_add_check_read_ops(transport_global, stream_global);
+    grpc_chttp2_list_add_check_read_ops(exec_ctx, transport_global,
+                                        stream_global);
   }
   if (slice) {
     gpr_slice_unref(*slice);
@@ -1739,7 +1660,8 @@
     GRPC_ERROR_UNREF(error);
     return;
   }
-  grpc_chttp2_list_add_check_read_ops(transport_global, stream_global);
+  grpc_chttp2_list_add_check_read_ops(exec_ctx, transport_global,
+                                      stream_global);
   if (close_reads && !stream_global->read_closed) {
     stream_global->read_closed_error = GRPC_ERROR_REF(error);
     stream_global->read_closed = true;
@@ -1920,6 +1842,10 @@
 
 static void drop_connection(grpc_exec_ctx *exec_ctx, grpc_chttp2_transport *t,
                             grpc_error *error) {
+  if (!grpc_error_get_int(error, GRPC_ERROR_INT_GRPC_STATUS, NULL)) {
+    error = grpc_error_set_int(error, GRPC_ERROR_INT_GRPC_STATUS,
+                               GRPC_STATUS_UNAVAILABLE);
+  }
   close_transport_locked(exec_ctx, t, GRPC_ERROR_REF(error));
   end_all_the_calls(exec_ctx, t, error);
 }
@@ -1955,16 +1881,12 @@
  * INPUT PROCESSING - PARSING
  */
 
-static void reading_action_locked(grpc_exec_ctx *exec_ctx,
-                                  grpc_chttp2_transport *t,
-                                  grpc_chttp2_stream *s_unused, void *arg);
 static void parsing_action(grpc_exec_ctx *exec_ctx, void *arg,
                            grpc_error *error);
-static void post_reading_action_locked(grpc_exec_ctx *exec_ctx,
-                                       grpc_chttp2_transport *t,
-                                       grpc_chttp2_stream *s_unused, void *arg);
-static void post_parse_locked(grpc_exec_ctx *exec_ctx, grpc_chttp2_transport *t,
-                              grpc_chttp2_stream *s_unused, void *arg);
+static void post_reading_action_locked(grpc_exec_ctx *exec_ctx, void *arg,
+                                       grpc_error *error);
+static void post_parse_locked(grpc_exec_ctx *exec_ctx, void *arg,
+                              grpc_error *error);
 
 static void reading_action(grpc_exec_ctx *exec_ctx, void *tp,
                            grpc_error *error) {
@@ -1972,16 +1894,20 @@
      reading_action_locked ->
        (parse_unlocked -> post_parse_locked)? ->
        post_reading_action_locked */
-  grpc_chttp2_run_with_global_lock(exec_ctx, tp, NULL, reading_action_locked,
-                                   GRPC_ERROR_REF(error), 0);
+  GPR_TIMER_BEGIN("reading_action", 0);
+  grpc_chttp2_transport *t = tp;
+  grpc_combiner_execute(exec_ctx, t->executor.combiner,
+                        &t->reading_action_locked, GRPC_ERROR_REF(error));
+  GPR_TIMER_END("reading_action", 0);
 }
 
-static void reading_action_locked(grpc_exec_ctx *exec_ctx,
-                                  grpc_chttp2_transport *t,
-                                  grpc_chttp2_stream *s_unused, void *arg) {
+static void reading_action_locked(grpc_exec_ctx *exec_ctx, void *tp,
+                                  grpc_error *error) {
+  GPR_TIMER_BEGIN("reading_action_locked", 0);
+
+  grpc_chttp2_transport *t = tp;
   grpc_chttp2_transport_global *transport_global = &t->global;
   grpc_chttp2_transport_parsing *transport_parsing = &t->parsing;
-  grpc_error *error = arg;
 
   GPR_ASSERT(!t->executor.parsing_active);
   if (!t->closed) {
@@ -1990,10 +1916,13 @@
     grpc_chttp2_stream_map_move_into(&t->new_stream_map,
                                      &t->parsing_stream_map);
     grpc_chttp2_prepare_to_read(transport_global, transport_parsing);
-    grpc_exec_ctx_sched(exec_ctx, &t->parsing_action, error, NULL);
+    grpc_exec_ctx_sched(exec_ctx, &t->parsing_action, GRPC_ERROR_REF(error),
+                        NULL);
   } else {
-    post_reading_action_locked(exec_ctx, t, s_unused, arg);
+    post_reading_action_locked(exec_ctx, t, error);
   }
+
+  GPR_TIMER_END("reading_action_locked", 0);
 }
 
 static grpc_error *try_http_parsing(grpc_exec_ctx *exec_ctx,
@@ -2045,13 +1974,15 @@
   for (i = 0; i < GPR_ARRAY_SIZE(errors); i++) {
     GRPC_ERROR_UNREF(errors[i]);
   }
+  grpc_combiner_execute(exec_ctx, t->executor.combiner, &t->post_parse_locked,
+                        err);
   GPR_TIMER_END("reading_action.parse", 0);
-  grpc_chttp2_run_with_global_lock(exec_ctx, t, NULL, post_parse_locked, err,
-                                   0);
 }
 
-static void post_parse_locked(grpc_exec_ctx *exec_ctx, grpc_chttp2_transport *t,
-                              grpc_chttp2_stream *s_unused, void *arg) {
+static void post_parse_locked(grpc_exec_ctx *exec_ctx, void *arg,
+                              grpc_error *error) {
+  GPR_TIMER_BEGIN("post_parse_locked", 0);
+  grpc_chttp2_transport *t = arg;
   grpc_chttp2_transport_global *transport_global = &t->global;
   grpc_chttp2_transport_parsing *transport_parsing = &t->parsing;
   /* copy parsing qbuf to global qbuf */
@@ -2077,7 +2008,7 @@
   if (t->post_parsing_op) {
     grpc_transport_op *op = t->post_parsing_op;
     t->post_parsing_op = NULL;
-    perform_transport_op_locked(exec_ctx, t, NULL, op);
+    perform_transport_op_locked(exec_ctx, op, GRPC_ERROR_NONE);
     gpr_free(op);
   }
   /* if a stream is in the stream map, and gets cancelled, we need to
@@ -2094,39 +2025,32 @@
     GRPC_CHTTP2_STREAM_UNREF(exec_ctx, stream_global, "chttp2");
   }
 
-  post_reading_action_locked(exec_ctx, t, s_unused, arg);
+  post_reading_action_locked(exec_ctx, t, error);
+  GPR_TIMER_END("post_parse_locked", 0);
 }
 
-static void post_reading_action_locked(grpc_exec_ctx *exec_ctx,
-                                       grpc_chttp2_transport *t,
-                                       grpc_chttp2_stream *s_unused,
-                                       void *arg) {
-  grpc_error *error = arg;
+static void post_reading_action_locked(grpc_exec_ctx *exec_ctx, void *arg,
+                                       grpc_error *error) {
+  GPR_TIMER_BEGIN("post_reading_action_locked", 0);
+  grpc_chttp2_transport *t = arg;
   bool keep_reading = false;
+  GRPC_ERROR_REF(error);
   if (error == GRPC_ERROR_NONE && t->closed) {
     error = GRPC_ERROR_CREATE("Transport closed");
   }
   if (error != GRPC_ERROR_NONE) {
-    if (!grpc_error_get_int(error, GRPC_ERROR_INT_GRPC_STATUS, NULL)) {
-      error = grpc_error_set_int(error, GRPC_ERROR_INT_GRPC_STATUS,
-                                 GRPC_STATUS_UNAVAILABLE);
-    }
     drop_connection(exec_ctx, t, GRPC_ERROR_REF(error));
     t->endpoint_reading = 0;
     if (grpc_http_write_state_trace) {
       gpr_log(GPR_DEBUG, "R:%p -> 0 ws=%s", t,
               write_state_name(t->executor.write_state));
     }
-    if (t->executor.write_state == GRPC_CHTTP2_WRITING_INACTIVE && t->ep) {
-      destroy_endpoint(exec_ctx, t);
-    }
   } else if (!t->closed) {
     keep_reading = true;
     REF_TRANSPORT(t, "keep_reading");
     prevent_endpoint_shutdown(t);
   }
   gpr_slice_buffer_reset_and_unref(&t->read_buffer);
-  GRPC_ERROR_UNREF(error);
 
   if (keep_reading) {
     grpc_endpoint_read(exec_ctx, t->ep, &t->read_buffer, &t->reading_action);
@@ -2135,6 +2059,9 @@
   } else {
     UNREF_TRANSPORT(exec_ctx, t, "reading_action");
   }
+  GRPC_ERROR_UNREF(error);
+
+  GPR_TIMER_END("post_reading_action_locked", 0);
 }
 
 /*******************************************************************************
@@ -2156,36 +2083,16 @@
  * POLLSET STUFF
  */
 
-static void add_to_pollset_locked(grpc_exec_ctx *exec_ctx,
-                                  grpc_chttp2_transport *t,
-                                  grpc_chttp2_stream *s_unused, void *pollset) {
-  if (t->ep) {
-    grpc_endpoint_add_to_pollset(exec_ctx, t->ep, pollset);
-  }
-}
-
-static void add_to_pollset_set_locked(grpc_exec_ctx *exec_ctx,
-                                      grpc_chttp2_transport *t,
-                                      grpc_chttp2_stream *s_unused,
-                                      void *pollset_set) {
-  if (t->ep) {
-    grpc_endpoint_add_to_pollset_set(exec_ctx, t->ep, pollset_set);
-  }
-}
-
 static void set_pollset(grpc_exec_ctx *exec_ctx, grpc_transport *gt,
                         grpc_stream *gs, grpc_pollset *pollset) {
-  /* TODO(ctiller): keep pollset alive */
-  grpc_chttp2_run_with_global_lock(exec_ctx, (grpc_chttp2_transport *)gt,
-                                   (grpc_chttp2_stream *)gs,
-                                   add_to_pollset_locked, pollset, 0);
+  grpc_chttp2_transport *t = (grpc_chttp2_transport *)gt;
+  grpc_endpoint_add_to_pollset(exec_ctx, t->ep, pollset);
 }
 
 static void set_pollset_set(grpc_exec_ctx *exec_ctx, grpc_transport *gt,
                             grpc_stream *gs, grpc_pollset_set *pollset_set) {
-  grpc_chttp2_run_with_global_lock(exec_ctx, (grpc_chttp2_transport *)gt,
-                                   (grpc_chttp2_stream *)gs,
-                                   add_to_pollset_set_locked, pollset_set, 0);
+  grpc_chttp2_transport *t = (grpc_chttp2_transport *)gt;
+  grpc_endpoint_add_to_pollset_set(exec_ctx, t->ep, pollset_set);
 }
 
 /*******************************************************************************
@@ -2197,6 +2104,7 @@
   if (gpr_unref(&bs->refs)) {
     GRPC_ERROR_UNREF(bs->error);
     gpr_slice_buffer_destroy(&bs->slices);
+    gpr_mu_destroy(&bs->slice_mu);
     gpr_free(bs);
   }
 }
@@ -2242,38 +2150,34 @@
   }
 }
 
-typedef struct {
-  grpc_chttp2_incoming_byte_stream *byte_stream;
-  gpr_slice *slice;
-  size_t max_size_hint;
-  grpc_closure *on_complete;
-} incoming_byte_stream_next_arg;
-
 static void incoming_byte_stream_next_locked(grpc_exec_ctx *exec_ctx,
-                                             grpc_chttp2_transport *t,
-                                             grpc_chttp2_stream *s,
-                                             void *argp) {
-  incoming_byte_stream_next_arg *arg = argp;
-  grpc_chttp2_incoming_byte_stream *bs =
-      (grpc_chttp2_incoming_byte_stream *)arg->byte_stream;
+                                             void *argp,
+                                             grpc_error *error_ignored) {
+  grpc_chttp2_incoming_byte_stream *bs = argp;
   grpc_chttp2_transport_global *transport_global = &bs->transport->global;
   grpc_chttp2_stream_global *stream_global = &bs->stream->global;
 
   if (bs->is_tail) {
-    incoming_byte_stream_update_flow_control(exec_ctx, transport_global,
-                                             stream_global, arg->max_size_hint,
-                                             bs->slices.length);
+    gpr_mu_lock(&bs->slice_mu);
+    size_t cur_length = bs->slices.length;
+    gpr_mu_unlock(&bs->slice_mu);
+    incoming_byte_stream_update_flow_control(
+        exec_ctx, transport_global, stream_global,
+        bs->next_action.max_size_hint, cur_length);
   }
+  gpr_mu_lock(&bs->slice_mu);
   if (bs->slices.count > 0) {
-    *arg->slice = gpr_slice_buffer_take_first(&bs->slices);
-    grpc_exec_ctx_sched(exec_ctx, arg->on_complete, GRPC_ERROR_NONE, NULL);
-  } else if (bs->error != GRPC_ERROR_NONE) {
-    grpc_exec_ctx_sched(exec_ctx, arg->on_complete, GRPC_ERROR_REF(bs->error),
+    *bs->next_action.slice = gpr_slice_buffer_take_first(&bs->slices);
+    grpc_exec_ctx_sched(exec_ctx, bs->next_action.on_complete, GRPC_ERROR_NONE,
                         NULL);
+  } else if (bs->error != GRPC_ERROR_NONE) {
+    grpc_exec_ctx_sched(exec_ctx, bs->next_action.on_complete,
+                        GRPC_ERROR_REF(bs->error), NULL);
   } else {
-    bs->on_next = arg->on_complete;
-    bs->next = arg->slice;
+    bs->on_next = bs->next_action.on_complete;
+    bs->next = bs->next_action.slice;
   }
+  gpr_mu_unlock(&bs->slice_mu);
   incoming_byte_stream_unref(exec_ctx, bs);
 }
 
@@ -2281,13 +2185,18 @@
                                      grpc_byte_stream *byte_stream,
                                      gpr_slice *slice, size_t max_size_hint,
                                      grpc_closure *on_complete) {
+  GPR_TIMER_BEGIN("incoming_byte_stream_next", 0);
   grpc_chttp2_incoming_byte_stream *bs =
       (grpc_chttp2_incoming_byte_stream *)byte_stream;
-  incoming_byte_stream_next_arg arg = {bs, slice, max_size_hint, on_complete};
   gpr_ref(&bs->refs);
-  grpc_chttp2_run_with_global_lock(exec_ctx, bs->transport, bs->stream,
-                                   incoming_byte_stream_next_locked, &arg,
-                                   sizeof(arg));
+  bs->next_action.slice = slice;
+  bs->next_action.max_size_hint = max_size_hint;
+  bs->next_action.on_complete = on_complete;
+  grpc_closure_init(&bs->next_action.closure, incoming_byte_stream_next_locked,
+                    bs);
+  grpc_combiner_execute(exec_ctx, bs->transport->executor.combiner,
+                        &bs->next_action.closure, GRPC_ERROR_NONE);
+  GPR_TIMER_END("incoming_byte_stream_next", 0);
   return 0;
 }
 
@@ -2295,9 +2204,8 @@
                                          grpc_byte_stream *byte_stream);
 
 static void incoming_byte_stream_destroy_locked(grpc_exec_ctx *exec_ctx,
-                                                grpc_chttp2_transport *t,
-                                                grpc_chttp2_stream *s,
-                                                void *byte_stream) {
+                                                void *byte_stream,
+                                                grpc_error *error_ignored) {
   grpc_chttp2_incoming_byte_stream *bs = byte_stream;
   GPR_ASSERT(bs->base.destroy == incoming_byte_stream_destroy);
   decrement_active_streams_locked(exec_ctx, &bs->transport->global,
@@ -2307,10 +2215,14 @@
 
 static void incoming_byte_stream_destroy(grpc_exec_ctx *exec_ctx,
                                          grpc_byte_stream *byte_stream) {
+  GPR_TIMER_BEGIN("incoming_byte_stream_destroy", 0);
   grpc_chttp2_incoming_byte_stream *bs =
       (grpc_chttp2_incoming_byte_stream *)byte_stream;
-  grpc_chttp2_run_with_global_lock(exec_ctx, bs->transport, bs->stream,
-                                   incoming_byte_stream_destroy_locked, bs, 0);
+  grpc_closure_init(&bs->destroy_action, incoming_byte_stream_destroy_locked,
+                    bs);
+  grpc_combiner_execute(exec_ctx, bs->transport->executor.combiner,
+                        &bs->destroy_action, GRPC_ERROR_NONE);
+  GPR_TIMER_END("incoming_byte_stream_destroy", 0);
 }
 
 typedef struct {
@@ -2318,90 +2230,45 @@
   gpr_slice slice;
 } incoming_byte_stream_push_arg;
 
-static void incoming_byte_stream_push_locked(grpc_exec_ctx *exec_ctx,
-                                             grpc_chttp2_transport *t,
-                                             grpc_chttp2_stream *s,
-                                             void *argp) {
-  incoming_byte_stream_push_arg *arg = argp;
-  grpc_chttp2_incoming_byte_stream *bs = arg->byte_stream;
-  if (bs->on_next != NULL) {
-    *bs->next = arg->slice;
-    grpc_exec_ctx_sched(exec_ctx, bs->on_next, GRPC_ERROR_NONE, NULL);
-    bs->on_next = NULL;
-  } else {
-    gpr_slice_buffer_add(&bs->slices, arg->slice);
-  }
-  incoming_byte_stream_unref(exec_ctx, bs);
-}
-
 void grpc_chttp2_incoming_byte_stream_push(grpc_exec_ctx *exec_ctx,
                                            grpc_chttp2_incoming_byte_stream *bs,
                                            gpr_slice slice) {
-  incoming_byte_stream_push_arg arg = {bs, slice};
-  gpr_ref(&bs->refs);
-  grpc_chttp2_run_with_global_lock(exec_ctx, bs->transport, bs->stream,
-                                   incoming_byte_stream_push_locked, &arg,
-                                   sizeof(arg));
+  gpr_mu_lock(&bs->slice_mu);
+  if (bs->on_next != NULL) {
+    *bs->next = slice;
+    grpc_exec_ctx_sched(exec_ctx, bs->on_next, GRPC_ERROR_NONE, NULL);
+    bs->on_next = NULL;
+  } else {
+    gpr_slice_buffer_add(&bs->slices, slice);
+  }
+  gpr_mu_unlock(&bs->slice_mu);
 }
 
-typedef struct {
-  grpc_chttp2_incoming_byte_stream *bs;
-  grpc_error *error;
-} bs_fail_args;
-
-static bs_fail_args *make_bs_fail_args(grpc_chttp2_incoming_byte_stream *bs,
-                                       grpc_error *error) {
-  bs_fail_args *a = gpr_malloc(sizeof(*a));
-  a->bs = bs;
-  a->error = error;
-  return a;
-}
-
-static void incoming_byte_stream_finished_failed_locked(
-    grpc_exec_ctx *exec_ctx, grpc_chttp2_transport *t, grpc_chttp2_stream *s,
-    void *argp) {
-  bs_fail_args *a = argp;
-  grpc_chttp2_incoming_byte_stream *bs = a->bs;
-  grpc_error *error = a->error;
-  gpr_free(a);
-  grpc_exec_ctx_sched(exec_ctx, bs->on_next, GRPC_ERROR_REF(error), NULL);
-  bs->on_next = NULL;
-  GRPC_ERROR_UNREF(bs->error);
-  bs->error = error;
-  incoming_byte_stream_unref(exec_ctx, bs);
-}
-
-static void incoming_byte_stream_finished_ok_locked(grpc_exec_ctx *exec_ctx,
-                                                    grpc_chttp2_transport *t,
-                                                    grpc_chttp2_stream *s,
-                                                    void *argp) {
-  grpc_chttp2_incoming_byte_stream *bs = argp;
+static void incoming_byte_stream_finished_locked(grpc_exec_ctx *exec_ctx,
+                                                 void *bsp, grpc_error *error) {
+  grpc_chttp2_incoming_byte_stream *bs = bsp;
+  if (error != GRPC_ERROR_NONE) {
+    grpc_exec_ctx_sched(exec_ctx, bs->on_next, GRPC_ERROR_REF(error), NULL);
+    bs->on_next = NULL;
+    GRPC_ERROR_UNREF(bs->error);
+    bs->error = error;
+  }
   incoming_byte_stream_unref(exec_ctx, bs);
 }
 
 void grpc_chttp2_incoming_byte_stream_finished(
     grpc_exec_ctx *exec_ctx, grpc_chttp2_incoming_byte_stream *bs,
     grpc_error *error, int from_parsing_thread) {
+  GPR_TIMER_BEGIN("grpc_chttp2_incoming_byte_stream_finished", 0);
   if (from_parsing_thread) {
-    if (error == GRPC_ERROR_NONE) {
-      grpc_chttp2_run_with_global_lock(exec_ctx, bs->transport, bs->stream,
-                                       incoming_byte_stream_finished_ok_locked,
-                                       bs, 0);
-    } else {
-      grpc_chttp2_run_with_global_lock(
-          exec_ctx, bs->transport, bs->stream,
-          incoming_byte_stream_finished_failed_locked,
-          make_bs_fail_args(bs, error), 0);
-    }
+    grpc_closure_init(&bs->finished_action,
+                      incoming_byte_stream_finished_locked, bs);
+    grpc_combiner_execute(exec_ctx, bs->transport->executor.combiner,
+                          &bs->finished_action, GRPC_ERROR_REF(error));
   } else {
-    if (error == GRPC_ERROR_NONE) {
-      incoming_byte_stream_finished_ok_locked(exec_ctx, bs->transport,
-                                              bs->stream, bs);
-    } else {
-      incoming_byte_stream_finished_failed_locked(
-          exec_ctx, bs->transport, bs->stream, make_bs_fail_args(bs, error));
-    }
+    incoming_byte_stream_finished_locked(exec_ctx, bs, error);
   }
+  GPR_TIMER_END("grpc_chttp2_incoming_byte_stream_finished", 0);
 }
 
 grpc_chttp2_incoming_byte_stream *grpc_chttp2_incoming_byte_stream_create(
@@ -2414,6 +2281,7 @@
   incoming_byte_stream->base.flags = flags;
   incoming_byte_stream->base.next = incoming_byte_stream_next;
   incoming_byte_stream->base.destroy = incoming_byte_stream_destroy;
+  gpr_mu_init(&incoming_byte_stream->slice_mu);
   gpr_ref_init(&incoming_byte_stream->refs, 2);
   incoming_byte_stream->next_message = NULL;
   incoming_byte_stream->transport = TRANSPORT_FROM_PARSING(transport_parsing);
diff --git a/src/core/ext/transport/chttp2/transport/internal.h b/src/core/ext/transport/chttp2/transport/internal.h
index d67c014..04b788b 100644
--- a/src/core/ext/transport/chttp2/transport/internal.h
+++ b/src/core/ext/transport/chttp2/transport/internal.h
@@ -48,6 +48,7 @@
 #include "src/core/ext/transport/chttp2/transport/hpack_parser.h"
 #include "src/core/ext/transport/chttp2/transport/incoming_metadata.h"
 #include "src/core/ext/transport/chttp2/transport/stream_map.h"
+#include "src/core/lib/iomgr/combiner.h"
 #include "src/core/lib/iomgr/endpoint.h"
 #include "src/core/lib/transport/connectivity_state.h"
 #include "src/core/lib/transport/transport_impl.h"
@@ -161,9 +162,20 @@
   grpc_chttp2_transport *transport;
   grpc_chttp2_stream *stream;
   int is_tail;
+
+  gpr_mu slice_mu;  // protects slices, on_next
   gpr_slice_buffer slices;
   grpc_closure *on_next;
   gpr_slice *next;
+
+  struct {
+    grpc_closure closure;
+    gpr_slice *slice;
+    size_t max_size_hint;
+    grpc_closure *on_complete;
+  } next_action;
+  grpc_closure destroy_action;
+  grpc_closure finished_action;
 };
 
 typedef struct {
@@ -296,23 +308,11 @@
   int64_t outgoing_window;
 };
 
-typedef void (*grpc_chttp2_locked_action)(grpc_exec_ctx *ctx,
-                                          grpc_chttp2_transport *t,
-                                          grpc_chttp2_stream *s, void *arg);
-
-typedef struct grpc_chttp2_executor_action_header {
-  grpc_chttp2_stream *stream;
-  grpc_chttp2_locked_action action;
-  struct grpc_chttp2_executor_action_header *next;
-  void *arg;
-} grpc_chttp2_executor_action_header;
-
 typedef enum {
+  /** no writing activity allowed */
+  GRPC_CHTTP2_WRITES_CORKED,
   /** no writing activity */
   GRPC_CHTTP2_WRITING_INACTIVE,
-  /** write has been requested, but not scheduled yet */
-  GRPC_CHTTP2_WRITE_REQUESTED_WITH_POLLER,
-  GRPC_CHTTP2_WRITE_REQUESTED_NO_POLLER,
   /** write has been requested and scheduled against the workqueue */
   GRPC_CHTTP2_WRITE_SCHEDULED,
   /** write has been initiated after being reaped from the workqueue */
@@ -333,7 +333,7 @@
   gpr_refcount shutdown_ep_refs;
 
   struct {
-    gpr_mu mu;
+    grpc_combiner *combiner;
 
     /** is a thread currently in the global lock */
     bool global_active;
@@ -341,9 +341,8 @@
     bool parsing_active;
     /** write execution state of the transport */
     grpc_chttp2_write_state write_state;
-
-    grpc_chttp2_executor_action_header *pending_actions_head;
-    grpc_chttp2_executor_action_header *pending_actions_tail;
+    /** has a check_read_ops been scheduled */
+    bool check_read_ops_scheduled;
   } executor;
 
   /** is the transport destroying itself? */
@@ -380,10 +379,16 @@
   grpc_closure writing_action;
   /** closure to start reading from the endpoint */
   grpc_closure reading_action;
+  grpc_closure reading_action_locked;
+  grpc_closure post_parse_locked;
   /** closure to actually do parsing */
   grpc_closure parsing_action;
   /** closure to initiate writing */
   grpc_closure initiate_writing;
+  /** closure to finish writing */
+  grpc_closure terminate_writing;
+  /** closure to flush read state up the stack */
+  grpc_closure initiate_read_flush_locked;
 
   /** incoming read bytes */
   gpr_slice_buffer read_buffer;
@@ -527,11 +532,16 @@
 };
 
 struct grpc_chttp2_stream {
+  grpc_chttp2_transport *t;
   grpc_stream_refcount *refcount;
   grpc_chttp2_stream_global global;
   grpc_chttp2_stream_writing writing;
   grpc_chttp2_stream_parsing parsing;
 
+  grpc_closure init_stream;
+  grpc_closure destroy_stream;
+  void *destroy_stream_arg;
+
   grpc_chttp2_stream_link links[STREAM_LIST_COUNT];
   uint8_t included[STREAM_LIST_COUNT];
 };
@@ -626,7 +636,7 @@
     grpc_chttp2_stream_global **stream_global);
 
 void grpc_chttp2_list_add_check_read_ops(
-    grpc_chttp2_transport_global *transport_global,
+    grpc_exec_ctx *exec_ctx, grpc_chttp2_transport_global *transport_global,
     grpc_chttp2_stream_global *stream_global);
 bool grpc_chttp2_list_remove_check_read_ops(
     grpc_chttp2_transport_global *transport_global,
@@ -706,12 +716,6 @@
     grpc_chttp2_stream_global *stream_global, grpc_closure **pclosure,
     grpc_error *error);
 
-void grpc_chttp2_run_with_global_lock(grpc_exec_ctx *exec_ctx,
-                                      grpc_chttp2_transport *transport,
-                                      grpc_chttp2_stream *optional_stream,
-                                      grpc_chttp2_locked_action action,
-                                      void *arg, size_t sizeof_arg);
-
 #define GRPC_CHTTP2_CLIENT_CONNECT_STRING "PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n"
 #define GRPC_CHTTP2_CLIENT_CONNECT_STRLEN \
   (sizeof(GRPC_CHTTP2_CLIENT_CONNECT_STRING) - 1)
diff --git a/src/core/ext/transport/chttp2/transport/parsing.c b/src/core/ext/transport/chttp2/transport/parsing.c
index 482cd55..0e6d579 100644
--- a/src/core/ext/transport/chttp2/transport/parsing.c
+++ b/src/core/ext/transport/chttp2/transport/parsing.c
@@ -177,7 +177,8 @@
       stream_global->seen_error = true;
       stream_global->exceeded_metadata_size =
           stream_parsing->exceeded_metadata_size;
-      grpc_chttp2_list_add_check_read_ops(transport_global, stream_global);
+      grpc_chttp2_list_add_check_read_ops(exec_ctx, transport_global,
+                                          stream_global);
     }
 
     /* flush stats to global stream state */
@@ -203,7 +204,8 @@
       stream_global->incoming_frames.tail->is_tail = 0;
     }
     if (stream_parsing->data_parser.incoming_frames.head != NULL) {
-      grpc_chttp2_list_add_check_read_ops(transport_global, stream_global);
+      grpc_chttp2_list_add_check_read_ops(exec_ctx, transport_global,
+                                          stream_global);
     }
     grpc_chttp2_incoming_frame_queue_merge(
         &stream_global->incoming_frames,
@@ -219,7 +221,8 @@
       GPR_SWAP(grpc_chttp2_incoming_metadata_buffer,
                stream_parsing->metadata_buffer[0],
                stream_global->received_initial_metadata);
-      grpc_chttp2_list_add_check_read_ops(transport_global, stream_global);
+      grpc_chttp2_list_add_check_read_ops(exec_ctx, transport_global,
+                                          stream_global);
     }
     if (!stream_global->published_trailing_metadata &&
         stream_parsing->got_metadata_on_parse[1]) {
@@ -228,7 +231,8 @@
       GPR_SWAP(grpc_chttp2_incoming_metadata_buffer,
                stream_parsing->metadata_buffer[1],
                stream_global->received_trailing_metadata);
-      grpc_chttp2_list_add_check_read_ops(transport_global, stream_global);
+      grpc_chttp2_list_add_check_read_ops(exec_ctx, transport_global,
+                                          stream_global);
     }
 
     if (stream_parsing->forced_close_error != GRPC_ERROR_NONE) {
diff --git a/src/core/ext/transport/chttp2/transport/stream_lists.c b/src/core/ext/transport/chttp2/transport/stream_lists.c
index 2eb5f5f..4dc4968 100644
--- a/src/core/ext/transport/chttp2/transport/stream_lists.c
+++ b/src/core/ext/transport/chttp2/transport/stream_lists.c
@@ -298,8 +298,15 @@
 }
 
 void grpc_chttp2_list_add_check_read_ops(
-    grpc_chttp2_transport_global *transport_global,
+    grpc_exec_ctx *exec_ctx, grpc_chttp2_transport_global *transport_global,
     grpc_chttp2_stream_global *stream_global) {
+  grpc_chttp2_transport *t = TRANSPORT_FROM_GLOBAL(transport_global);
+  if (!t->executor.check_read_ops_scheduled) {
+    grpc_combiner_execute_finally(exec_ctx, t->executor.combiner,
+                                  &t->initiate_read_flush_locked,
+                                  GRPC_ERROR_NONE, false);
+    t->executor.check_read_ops_scheduled = true;
+  }
   stream_list_add(TRANSPORT_FROM_GLOBAL(transport_global),
                   STREAM_FROM_GLOBAL(stream_global),
                   GRPC_CHTTP2_LIST_CHECK_READ_OPS);
diff --git a/src/core/ext/transport/chttp2/transport/writing.c b/src/core/ext/transport/chttp2/transport/writing.c
index 311b26e..979515b 100644
--- a/src/core/ext/transport/chttp2/transport/writing.c
+++ b/src/core/ext/transport/chttp2/transport/writing.c
@@ -55,15 +55,6 @@
       transport_global->settings[GRPC_ACKED_SETTINGS]
                                 [GRPC_CHTTP2_SETTINGS_MAX_FRAME_SIZE];
 
-  /* simple writes are queued to qbuf, and flushed here */
-  gpr_slice_buffer_swap(&transport_global->qbuf, &transport_writing->outbuf);
-  GPR_ASSERT(transport_global->qbuf.count == 0);
-
-  grpc_chttp2_hpack_compressor_set_max_table_size(
-      &transport_writing->hpack_compressor,
-      transport_global->settings[GRPC_PEER_SETTINGS]
-                                [GRPC_CHTTP2_SETTINGS_HEADER_TABLE_SIZE]);
-
   if (transport_global->dirtied_local_settings &&
       !transport_global->sent_local_settings) {
     gpr_slice_buffer_add(
@@ -77,6 +68,16 @@
     transport_global->sent_local_settings = 1;
   }
 
+  /* simple writes are queued to qbuf, and flushed here */
+  gpr_slice_buffer_move_into(&transport_global->qbuf,
+                             &transport_writing->outbuf);
+  GPR_ASSERT(transport_global->qbuf.count == 0);
+
+  grpc_chttp2_hpack_compressor_set_max_table_size(
+      &transport_writing->hpack_compressor,
+      transport_global->settings[GRPC_PEER_SETTINGS]
+                                [GRPC_CHTTP2_SETTINGS_HEADER_TABLE_SIZE]);
+
   GRPC_CHTTP2_FLOW_MOVE_TRANSPORT("write", transport_writing, outgoing_window,
                                   transport_global, outgoing_window);
   if (transport_writing->outgoing_window > 0) {
@@ -344,6 +345,7 @@
 void grpc_chttp2_cleanup_writing(
     grpc_exec_ctx *exec_ctx, grpc_chttp2_transport_global *transport_global,
     grpc_chttp2_transport_writing *transport_writing) {
+  GPR_TIMER_BEGIN("grpc_chttp2_cleanup_writing", 0);
   grpc_chttp2_stream_writing *stream_writing;
   grpc_chttp2_stream_global *stream_global;
 
@@ -382,4 +384,5 @@
     GRPC_CHTTP2_STREAM_UNREF(exec_ctx, stream_global, "chttp2_writing");
   }
   gpr_slice_buffer_reset_and_unref(&transport_writing->outbuf);
+  GPR_TIMER_END("grpc_chttp2_cleanup_writing", 0);
 }
diff --git a/src/core/lib/channel/channel_stack.c b/src/core/lib/channel/channel_stack.c
index 98f304f..0655b93 100644
--- a/src/core/lib/channel/channel_stack.c
+++ b/src/core/lib/channel/channel_stack.c
@@ -32,6 +32,7 @@
  */
 
 #include "src/core/lib/channel/channel_stack.h"
+#include <grpc/support/alloc.h>
 #include <grpc/support/log.h>
 
 #include <stdlib.h>
@@ -270,21 +271,27 @@
       sizeof(grpc_call_stack)));
 }
 
+static void destroy_op(grpc_exec_ctx *exec_ctx, void *op, grpc_error *error) {
+  gpr_free(op);
+}
+
 void grpc_call_element_send_cancel(grpc_exec_ctx *exec_ctx,
                                    grpc_call_element *cur_elem) {
-  grpc_transport_stream_op op;
-  memset(&op, 0, sizeof(op));
-  op.cancel_error = GRPC_ERROR_CANCELLED;
-  grpc_call_next_op(exec_ctx, cur_elem, &op);
+  grpc_transport_stream_op *op = gpr_malloc(sizeof(*op));
+  memset(op, 0, sizeof(*op));
+  op->cancel_error = GRPC_ERROR_CANCELLED;
+  op->on_complete = grpc_closure_create(destroy_op, op);
+  grpc_call_next_op(exec_ctx, cur_elem, op);
 }
 
 void grpc_call_element_send_cancel_with_message(grpc_exec_ctx *exec_ctx,
                                                 grpc_call_element *cur_elem,
                                                 grpc_status_code status,
                                                 gpr_slice *optional_message) {
-  grpc_transport_stream_op op;
-  memset(&op, 0, sizeof(op));
-  grpc_transport_stream_op_add_cancellation_with_message(&op, status,
+  grpc_transport_stream_op *op = gpr_malloc(sizeof(*op));
+  memset(op, 0, sizeof(*op));
+  op->on_complete = grpc_closure_create(destroy_op, op);
+  grpc_transport_stream_op_add_cancellation_with_message(op, status,
                                                          optional_message);
-  grpc_call_next_op(exec_ctx, cur_elem, &op);
+  grpc_call_next_op(exec_ctx, cur_elem, op);
 }
diff --git a/src/core/lib/channel/compress_filter.c b/src/core/lib/channel/compress_filter.c
index 134180e..0981d59 100644
--- a/src/core/lib/channel/compress_filter.c
+++ b/src/core/lib/channel/compress_filter.c
@@ -60,7 +60,7 @@
   /** If true, contents of \a compression_algorithm are authoritative */
   int has_compression_algorithm;
 
-  grpc_transport_stream_op send_op;
+  grpc_transport_stream_op *send_op;
   uint32_t send_length;
   uint32_t send_flags;
   gpr_slice incoming_slice;
@@ -199,11 +199,11 @@
 
   grpc_slice_buffer_stream_init(&calld->replacement_stream, &calld->slices,
                                 calld->send_flags);
-  calld->send_op.send_message = &calld->replacement_stream.base;
-  calld->post_send = calld->send_op.on_complete;
-  calld->send_op.on_complete = &calld->send_done;
+  calld->send_op->send_message = &calld->replacement_stream.base;
+  calld->post_send = calld->send_op->on_complete;
+  calld->send_op->on_complete = &calld->send_done;
 
-  grpc_call_next_op(exec_ctx, elem, &calld->send_op);
+  grpc_call_next_op(exec_ctx, elem, calld->send_op);
 }
 
 static void got_slice(grpc_exec_ctx *exec_ctx, void *elemp, grpc_error *error) {
@@ -220,7 +220,7 @@
 static void continue_send_message(grpc_exec_ctx *exec_ctx,
                                   grpc_call_element *elem) {
   call_data *calld = elem->call_data;
-  while (grpc_byte_stream_next(exec_ctx, calld->send_op.send_message,
+  while (grpc_byte_stream_next(exec_ctx, calld->send_op->send_message,
                                &calld->incoming_slice, ~(size_t)0,
                                &calld->got_slice)) {
     gpr_slice_buffer_add(&calld->slices, calld->incoming_slice);
@@ -243,7 +243,7 @@
   }
   if (op->send_message != NULL && !skip_compression(elem) &&
       0 == (op->send_message->flags & GRPC_WRITE_NO_COMPRESS)) {
-    calld->send_op = *op;
+    calld->send_op = op;
     calld->send_length = op->send_message->length;
     calld->send_flags = op->send_message->flags;
     continue_send_message(exec_ctx, elem);
diff --git a/src/core/lib/iomgr/closure.c b/src/core/lib/iomgr/closure.c
index 0b6c3b2..1ba0a5c 100644
--- a/src/core/lib/iomgr/closure.c
+++ b/src/core/lib/iomgr/closure.c
@@ -41,6 +41,10 @@
   closure->cb_arg = cb_arg;
 }
 
+void grpc_closure_list_init(grpc_closure_list *closure_list) {
+  closure_list->head = closure_list->tail = NULL;
+}
+
 void grpc_closure_list_append(grpc_closure_list *closure_list,
                               grpc_closure *closure, grpc_error *error) {
   if (closure == NULL) {
diff --git a/src/core/lib/iomgr/closure.h b/src/core/lib/iomgr/closure.h
index 08e59a1..c1a22b6 100644
--- a/src/core/lib/iomgr/closure.h
+++ b/src/core/lib/iomgr/closure.h
@@ -37,6 +37,7 @@
 #include <grpc/support/port_platform.h>
 #include <stdbool.h>
 #include "src/core/lib/iomgr/error.h"
+#include "src/core/lib/support/mpscq.h"
 
 struct grpc_closure;
 typedef struct grpc_closure grpc_closure;
@@ -60,6 +61,14 @@
 
 /** A closure over a grpc_iomgr_cb_func. */
 struct grpc_closure {
+  /** Once queued, next indicates the next queued closure; before then, scratch
+   *  space */
+  union {
+    grpc_closure *next;
+    gpr_mpscq_node atm_next;
+    uintptr_t scratch;
+  } next_data;
+
   /** Bound callback. */
   grpc_iomgr_cb_func cb;
 
@@ -68,13 +77,6 @@
 
   /** Once queued, the result of the closure. Before then: scratch space */
   grpc_error *error;
-
-  /** Once queued, next indicates the next queued closure; before then, scratch
-   *  space */
-  union {
-    grpc_closure *next;
-    uintptr_t scratch;
-  } next_data;
 };
 
 /** Initializes \a closure with \a cb and \a cb_arg. */
@@ -87,6 +89,8 @@
 #define GRPC_CLOSURE_LIST_INIT \
   { NULL, NULL }
 
+void grpc_closure_list_init(grpc_closure_list *list);
+
 /** add \a closure to the end of \a list
     and set \a closure's result to \a error */
 void grpc_closure_list_append(grpc_closure_list *list, grpc_closure *closure,
diff --git a/src/core/lib/iomgr/combiner.c b/src/core/lib/iomgr/combiner.c
new file mode 100644
index 0000000..831bdb4
--- /dev/null
+++ b/src/core/lib/iomgr/combiner.c
@@ -0,0 +1,293 @@
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include "src/core/lib/iomgr/combiner.h"
+
+#include <string.h>
+
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+
+#include "src/core/lib/iomgr/workqueue.h"
+#include "src/core/lib/profiling/timers.h"
+
+int grpc_combiner_trace = 0;
+
+#define GRPC_COMBINER_TRACE(fn) \
+  do {                          \
+    if (grpc_combiner_trace) {  \
+      fn;                       \
+    }                           \
+  } while (0)
+
+struct grpc_combiner {
+  grpc_workqueue *optional_workqueue;
+  gpr_mpscq queue;
+  // state is:
+  // lower bit - zero if orphaned
+  // other bits - number of items queued on the lock
+  gpr_atm state;
+  bool take_async_break_before_final_list;
+  grpc_closure_list final_list;
+  grpc_closure continue_finishing;
+};
+
+grpc_combiner *grpc_combiner_create(grpc_workqueue *optional_workqueue) {
+  grpc_combiner *lock = gpr_malloc(sizeof(*lock));
+  lock->optional_workqueue = optional_workqueue;
+  gpr_atm_no_barrier_store(&lock->state, 1);
+  gpr_mpscq_init(&lock->queue);
+  lock->take_async_break_before_final_list = false;
+  grpc_closure_list_init(&lock->final_list);
+  GRPC_COMBINER_TRACE(gpr_log(GPR_DEBUG, "C:%p create", lock));
+  return lock;
+}
+
+static void really_destroy(grpc_exec_ctx *exec_ctx, grpc_combiner *lock) {
+  GRPC_COMBINER_TRACE(gpr_log(GPR_DEBUG, "C:%p really_destroy", lock));
+  GPR_ASSERT(gpr_atm_no_barrier_load(&lock->state) == 0);
+  gpr_mpscq_destroy(&lock->queue);
+  GRPC_WORKQUEUE_UNREF(exec_ctx, lock->optional_workqueue, "combiner");
+  gpr_free(lock);
+}
+
+void grpc_combiner_destroy(grpc_exec_ctx *exec_ctx, grpc_combiner *lock) {
+  gpr_atm old_state = gpr_atm_full_fetch_add(&lock->state, -1);
+  GRPC_COMBINER_TRACE(gpr_log(
+      GPR_DEBUG, "C:%p really_destroy old_state=%" PRIdPTR, lock, old_state));
+  if (old_state == 1) {
+    really_destroy(exec_ctx, lock);
+  }
+}
+
+static bool maybe_finish_one(grpc_exec_ctx *exec_ctx, grpc_combiner *lock);
+static void finish(grpc_exec_ctx *exec_ctx, grpc_combiner *lock);
+
+static void continue_finishing_mainline(grpc_exec_ctx *exec_ctx, void *arg,
+                                        grpc_error *error) {
+  GPR_TIMER_BEGIN("combiner.continue_executing_mainline", 0);
+  grpc_combiner *lock = arg;
+  GRPC_COMBINER_TRACE(
+      gpr_log(GPR_DEBUG, "C:%p continue_finishing_mainline", lock));
+  GPR_ASSERT(exec_ctx->active_combiner == NULL);
+  exec_ctx->active_combiner = lock;
+  if (maybe_finish_one(exec_ctx, lock)) finish(exec_ctx, lock);
+  GPR_ASSERT(exec_ctx->active_combiner == lock);
+  exec_ctx->active_combiner = NULL;
+  GPR_TIMER_END("combiner.continue_executing_mainline", 0);
+}
+
+static void execute_final(grpc_exec_ctx *exec_ctx, grpc_combiner *lock) {
+  GPR_TIMER_BEGIN("combiner.execute_final", 0);
+  grpc_closure *c = lock->final_list.head;
+  GPR_ASSERT(c != NULL);
+  grpc_closure_list_init(&lock->final_list);
+  lock->take_async_break_before_final_list = false;
+  int loops = 0;
+  while (c != NULL) {
+    GRPC_COMBINER_TRACE(
+        gpr_log(GPR_DEBUG, "C:%p execute_final[%d] c=%p", lock, loops, c));
+    grpc_closure *next = c->next_data.next;
+    grpc_error *error = c->error;
+    c->cb(exec_ctx, c->cb_arg, error);
+    GRPC_ERROR_UNREF(error);
+    c = next;
+    loops++;
+  }
+  GPR_TIMER_END("combiner.execute_final", 0);
+}
+
+static void continue_executing_final(grpc_exec_ctx *exec_ctx, void *arg,
+                                     grpc_error *error) {
+  GPR_TIMER_BEGIN("combiner.continue_executing_final", 0);
+  grpc_combiner *lock = arg;
+  GRPC_COMBINER_TRACE(
+      gpr_log(GPR_DEBUG, "C:%p continue_executing_final", lock));
+  GPR_ASSERT(exec_ctx->active_combiner == NULL);
+  exec_ctx->active_combiner = lock;
+  // quick peek to see if new things have turned up on the queue: if so, go back
+  // to executing them before the final list
+  if ((gpr_atm_acq_load(&lock->state) >> 1) > 1) {
+    if (maybe_finish_one(exec_ctx, lock)) finish(exec_ctx, lock);
+  } else {
+    execute_final(exec_ctx, lock);
+    finish(exec_ctx, lock);
+  }
+  GPR_ASSERT(exec_ctx->active_combiner == lock);
+  exec_ctx->active_combiner = NULL;
+  GPR_TIMER_END("combiner.continue_executing_final", 0);
+}
+
+static bool start_execute_final(grpc_exec_ctx *exec_ctx, grpc_combiner *lock) {
+  GPR_TIMER_BEGIN("combiner.start_execute_final", 0);
+  GPR_ASSERT(exec_ctx->active_combiner == lock);
+  GRPC_COMBINER_TRACE(
+      gpr_log(GPR_DEBUG,
+              "C:%p start_execute_final take_async_break_before_final_list=%d",
+              lock, lock->take_async_break_before_final_list));
+  if (lock->take_async_break_before_final_list) {
+    grpc_closure_init(&lock->continue_finishing, continue_executing_final,
+                      lock);
+    grpc_exec_ctx_sched(exec_ctx, &lock->continue_finishing, GRPC_ERROR_NONE,
+                        GRPC_WORKQUEUE_REF(lock->optional_workqueue, "sched"));
+    GPR_TIMER_END("combiner.start_execute_final", 0);
+    return false;
+  } else {
+    execute_final(exec_ctx, lock);
+    GPR_TIMER_END("combiner.start_execute_final", 0);
+    return true;
+  }
+}
+
+static bool maybe_finish_one(grpc_exec_ctx *exec_ctx, grpc_combiner *lock) {
+  GPR_TIMER_BEGIN("combiner.maybe_finish_one", 0);
+  gpr_mpscq_node *n = gpr_mpscq_pop(&lock->queue);
+  GRPC_COMBINER_TRACE(
+      gpr_log(GPR_DEBUG, "C:%p maybe_finish_one n=%p", lock, n));
+  GPR_ASSERT(exec_ctx->active_combiner == lock);
+  if (n == NULL) {
+    // Queue is in an transiently inconsistent state: a new item is being queued
+    // but is not visible to this thread yet.
+    // Use this as a cue that we should go off and do something else for a while
+    // (and come back later)
+    grpc_closure_init(&lock->continue_finishing, continue_finishing_mainline,
+                      lock);
+    grpc_exec_ctx_sched(exec_ctx, &lock->continue_finishing, GRPC_ERROR_NONE,
+                        GRPC_WORKQUEUE_REF(lock->optional_workqueue, "sched"));
+    GPR_TIMER_END("combiner.maybe_finish_one", 0);
+    return false;
+  }
+  grpc_closure *cl = (grpc_closure *)n;
+  grpc_error *error = cl->error;
+  cl->cb(exec_ctx, cl->cb_arg, error);
+  GRPC_ERROR_UNREF(error);
+  GPR_TIMER_END("combiner.maybe_finish_one", 0);
+  return true;
+}
+
+static void finish(grpc_exec_ctx *exec_ctx, grpc_combiner *lock) {
+  bool (*executor)(grpc_exec_ctx * exec_ctx, grpc_combiner * lock);
+  GPR_TIMER_BEGIN("combiner.finish", 0);
+  int loops = 0;
+  do {
+    executor = maybe_finish_one;
+    gpr_atm old_state = gpr_atm_full_fetch_add(&lock->state, -2);
+    GRPC_COMBINER_TRACE(gpr_log(GPR_DEBUG,
+                                "C:%p finish[%d] old_state=%" PRIdPTR, lock,
+                                loops, old_state));
+    switch (old_state) {
+      default:
+        // we have multiple queued work items: just continue executing them
+        break;
+      case 5:  // we're down to one queued item: if it's the final list we
+      case 4:  // should do that
+        if (!grpc_closure_list_empty(lock->final_list)) {
+          executor = start_execute_final;
+        }
+        break;
+      case 3:  // had one count, one unorphaned --> unlocked unorphaned
+        GPR_TIMER_END("combiner.finish", 0);
+        return;
+      case 2:  // and one count, one orphaned --> unlocked and orphaned
+        really_destroy(exec_ctx, lock);
+        GPR_TIMER_END("combiner.finish", 0);
+        return;
+      case 1:
+      case 0:
+        // these values are illegal - representing an already unlocked or
+        // deleted lock
+        GPR_UNREACHABLE_CODE(return );
+    }
+    loops++;
+  } while (executor(exec_ctx, lock));
+  GPR_TIMER_END("combiner.finish", 0);
+}
+
+void grpc_combiner_execute(grpc_exec_ctx *exec_ctx, grpc_combiner *lock,
+                           grpc_closure *cl, grpc_error *error) {
+  GRPC_COMBINER_TRACE(
+      gpr_log(GPR_DEBUG, "C:%p grpc_combiner_execute c=%p", lock, cl));
+  GPR_TIMER_BEGIN("combiner.execute", 0);
+  gpr_atm last = gpr_atm_full_fetch_add(&lock->state, 2);
+  GPR_ASSERT(last & 1);  // ensure lock has not been destroyed
+  if (last == 1) {
+    exec_ctx->active_combiner = lock;
+    GPR_TIMER_BEGIN("combiner.execute_first_cb", 0);
+    cl->cb(exec_ctx, cl->cb_arg, error);
+    GPR_TIMER_END("combiner.execute_first_cb", 0);
+    GRPC_ERROR_UNREF(error);
+    finish(exec_ctx, lock);
+    GPR_ASSERT(exec_ctx->active_combiner == lock);
+    exec_ctx->active_combiner = NULL;
+  } else {
+    cl->error = error;
+    gpr_mpscq_push(&lock->queue, &cl->next_data.atm_next);
+  }
+  GPR_TIMER_END("combiner.execute", 0);
+}
+
+static void enqueue_finally(grpc_exec_ctx *exec_ctx, void *closure,
+                            grpc_error *error) {
+  grpc_combiner_execute_finally(exec_ctx, exec_ctx->active_combiner, closure,
+                                GRPC_ERROR_REF(error), false);
+}
+
+void grpc_combiner_execute_finally(grpc_exec_ctx *exec_ctx, grpc_combiner *lock,
+                                   grpc_closure *closure, grpc_error *error,
+                                   bool force_async_break) {
+  GRPC_COMBINER_TRACE(gpr_log(
+      GPR_DEBUG,
+      "C:%p grpc_combiner_execute_finally c=%p force_async_break=%d; ac=%p",
+      lock, closure, force_async_break, exec_ctx->active_combiner));
+  GPR_TIMER_BEGIN("combiner.execute_finally", 0);
+  if (exec_ctx->active_combiner != lock) {
+    GPR_TIMER_MARK("slowpath", 0);
+    grpc_combiner_execute(exec_ctx, lock,
+                          grpc_closure_create(enqueue_finally, closure), error);
+    GPR_TIMER_END("combiner.execute_finally", 0);
+    return;
+  }
+
+  if (force_async_break) {
+    lock->take_async_break_before_final_list = true;
+  }
+  if (grpc_closure_list_empty(lock->final_list)) {
+    gpr_atm_full_fetch_add(&lock->state, 2);
+  }
+  grpc_closure_list_append(&lock->final_list, closure, error);
+  GPR_TIMER_END("combiner.execute_finally", 0);
+}
+
+void grpc_combiner_force_async_finally(grpc_combiner *lock) {
+  lock->take_async_break_before_final_list = true;
+}
diff --git a/src/core/lib/iomgr/combiner.h b/src/core/lib/iomgr/combiner.h
new file mode 100644
index 0000000..1409db2
--- /dev/null
+++ b/src/core/lib/iomgr/combiner.h
@@ -0,0 +1,71 @@
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifndef GRPC_CORE_LIB_IOMGR_COMBINER_H
+#define GRPC_CORE_LIB_IOMGR_COMBINER_H
+
+#include <stddef.h>
+
+#include <grpc/support/atm.h>
+#include "src/core/lib/iomgr/exec_ctx.h"
+#include "src/core/lib/support/mpscq.h"
+
+// Provides serialized access to some resource.
+// Each action queued on a combiner is executed serially in a borrowed thread.
+// The actual thread executing actions may change over time (but there will only
+// every be one at a time).
+
+// Initialize the lock, with an optional workqueue to shift load to when
+// necessary
+grpc_combiner *grpc_combiner_create(grpc_workqueue *optional_workqueue);
+// Destroy the lock
+void grpc_combiner_destroy(grpc_exec_ctx *exec_ctx, grpc_combiner *lock);
+// Execute \a action within the lock.
+void grpc_combiner_execute(grpc_exec_ctx *exec_ctx, grpc_combiner *lock,
+                           grpc_closure *closure, grpc_error *error);
+// Execute \a action within the lock just prior to unlocking.
+// if \a hint_async_break is true, the combiner tries to hand execution to
+// another thread before finishing the primary queue of combined closures and
+// executing the finally list.
+// Deprecation warning: \a hint_async_break will be removed in a future version
+// Takes a very slow and round-about path if not called from a
+// grpc_combiner_execute closure.
+void grpc_combiner_execute_finally(grpc_exec_ctx *exec_ctx, grpc_combiner *lock,
+                                   grpc_closure *closure, grpc_error *error,
+                                   bool hint_async_break);
+// Deprecated: force the finally list execution onto another thread
+void grpc_combiner_force_async_finally(grpc_combiner *lock);
+
+extern int grpc_combiner_trace;
+
+#endif /* GRPC_CORE_LIB_IOMGR_COMBINER_H */
diff --git a/src/core/lib/iomgr/error.c b/src/core/lib/iomgr/error.c
index 149c556..e366961 100644
--- a/src/core/lib/iomgr/error.c
+++ b/src/core/lib/iomgr/error.c
@@ -332,7 +332,7 @@
   return new;
 }
 
-static const char *no_error_string = "null";
+static const char *no_error_string = "\"No Error\"";
 static const char *oom_error_string = "\"Out of memory\"";
 static const char *cancelled_error_string = "\"Cancelled\"";
 
diff --git a/src/core/lib/iomgr/ev_epoll_linux.c b/src/core/lib/iomgr/ev_epoll_linux.c
index eba3471..740920d 100644
--- a/src/core/lib/iomgr/ev_epoll_linux.c
+++ b/src/core/lib/iomgr/ev_epoll_linux.c
@@ -1531,6 +1531,8 @@
 
 static void pollset_add_fd(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
                            grpc_fd *fd) {
+  GPR_TIMER_BEGIN("pollset_add_fd", 0);
+
   grpc_error *error = GRPC_ERROR_NONE;
 
   gpr_mu_lock(&pollset->mu);
@@ -1643,6 +1645,8 @@
   gpr_mu_unlock(&pollset->mu);
 
   GRPC_LOG_IF_ERROR("pollset_add_fd", error);
+
+  GPR_TIMER_END("pollset_add_fd", 0);
 }
 
 /*******************************************************************************
diff --git a/src/core/lib/iomgr/exec_ctx.h b/src/core/lib/iomgr/exec_ctx.h
index 917f332..1895ee6 100644
--- a/src/core/lib/iomgr/exec_ctx.h
+++ b/src/core/lib/iomgr/exec_ctx.h
@@ -40,8 +40,8 @@
 
 /** A workqueue represents a list of work to be executed asynchronously.
     Forward declared here to avoid a circular dependency with workqueue.h. */
-struct grpc_workqueue;
 typedef struct grpc_workqueue grpc_workqueue;
+typedef struct grpc_combiner grpc_combiner;
 
 #ifndef GRPC_EXECUTION_CONTEXT_SANITIZER
 /** Execution context.
@@ -66,13 +66,15 @@
  */
 struct grpc_exec_ctx {
   grpc_closure_list closure_list;
+  /** currently active combiner: updated only via combiner.c */
+  grpc_combiner *active_combiner;
   bool cached_ready_to_finish;
   void *check_ready_to_finish_arg;
   bool (*check_ready_to_finish)(grpc_exec_ctx *exec_ctx, void *arg);
 };
 
 #define GRPC_EXEC_CTX_INIT_WITH_FINISH_CHECK(finish_check, finish_check_arg) \
-  { GRPC_CLOSURE_LIST_INIT, false, finish_check_arg, finish_check }
+  { GRPC_CLOSURE_LIST_INIT, NULL, false, finish_check_arg, finish_check }
 #else
 struct grpc_exec_ctx {
   bool cached_ready_to_finish;
diff --git a/src/core/lib/iomgr/tcp_posix.c b/src/core/lib/iomgr/tcp_posix.c
index 974d5ae..9276772 100644
--- a/src/core/lib/iomgr/tcp_posix.c
+++ b/src/core/lib/iomgr/tcp_posix.c
@@ -379,10 +379,19 @@
   }
 
   if (!tcp_flush(tcp, &error)) {
+    if (grpc_tcp_trace) {
+      gpr_log(GPR_DEBUG, "write: delayed");
+    }
     grpc_fd_notify_on_write(exec_ctx, tcp->em_fd, &tcp->write_closure);
   } else {
     cb = tcp->write_cb;
     tcp->write_cb = NULL;
+    if (grpc_tcp_trace) {
+      const char *str = grpc_error_string(error);
+      gpr_log(GPR_DEBUG, "write: %s", str);
+      grpc_error_free_string(str);
+    }
+
     GPR_TIMER_BEGIN("tcp_handle_write.cb", 0);
     cb->cb(exec_ctx, cb->cb_arg, error);
     GPR_TIMER_END("tcp_handle_write.cb", 0);
@@ -425,8 +434,16 @@
   if (!tcp_flush(tcp, &error)) {
     TCP_REF(tcp, "write");
     tcp->write_cb = cb;
+    if (grpc_tcp_trace) {
+      gpr_log(GPR_DEBUG, "write: delayed");
+    }
     grpc_fd_notify_on_write(exec_ctx, tcp->em_fd, &tcp->write_closure);
   } else {
+    if (grpc_tcp_trace) {
+      const char *str = grpc_error_string(error);
+      gpr_log(GPR_DEBUG, "write: %s", str);
+      grpc_error_free_string(str);
+    }
     grpc_exec_ctx_sched(exec_ctx, cb, error, NULL);
   }
 
diff --git a/src/core/lib/iomgr/workqueue.h b/src/core/lib/iomgr/workqueue.h
index 7156e49..b2805dc 100644
--- a/src/core/lib/iomgr/workqueue.h
+++ b/src/core/lib/iomgr/workqueue.h
@@ -50,10 +50,6 @@
 
 /* grpc_workqueue is forward declared in exec_ctx.h */
 
-/* Deprecated: do not use.
-   This has *already* been removed in a future commit. */
-void grpc_workqueue_flush(grpc_exec_ctx *exec_ctx, grpc_workqueue *workqueue);
-
 /* Reference counting functions. Use the macro's always
    (GRPC_WORKQUEUE_{REF,UNREF}).
 
diff --git a/src/core/lib/iomgr/workqueue_posix.c b/src/core/lib/iomgr/workqueue_posix.c
index e0d6dac..ecfea68 100644
--- a/src/core/lib/iomgr/workqueue_posix.c
+++ b/src/core/lib/iomgr/workqueue_posix.c
@@ -44,6 +44,7 @@
 #include <grpc/support/useful.h>
 
 #include "src/core/lib/iomgr/ev_posix.h"
+#include "src/core/lib/profiling/timers.h"
 
 static void on_readable(grpc_exec_ctx *exec_ctx, void *arg, grpc_error *error);
 
@@ -52,8 +53,7 @@
   char name[32];
   *workqueue = gpr_malloc(sizeof(grpc_workqueue));
   gpr_ref_init(&(*workqueue)->refs, 1);
-  gpr_mu_init(&(*workqueue)->mu);
-  (*workqueue)->closure_list.head = (*workqueue)->closure_list.tail = NULL;
+  gpr_atm_no_barrier_store(&(*workqueue)->state, 1);
   grpc_error *err = grpc_wakeup_fd_init(&(*workqueue)->wakeup_fd);
   if (err != GRPC_ERROR_NONE) {
     gpr_free(*workqueue);
@@ -62,6 +62,7 @@
   sprintf(name, "workqueue:%p", (void *)(*workqueue));
   (*workqueue)->wakeup_read_fd = grpc_fd_create(
       GRPC_WAKEUP_FD_GET_READ_FD(&(*workqueue)->wakeup_fd), name);
+  gpr_mpscq_init(&(*workqueue)->queue);
   grpc_closure_init(&(*workqueue)->read_closure, on_readable, *workqueue);
   grpc_fd_notify_on_read(exec_ctx, (*workqueue)->wakeup_read_fd,
                          &(*workqueue)->read_closure);
@@ -70,57 +71,79 @@
 
 static void workqueue_destroy(grpc_exec_ctx *exec_ctx,
                               grpc_workqueue *workqueue) {
-  grpc_exec_ctx_enqueue_list(exec_ctx, &workqueue->closure_list, NULL);
   grpc_fd_shutdown(exec_ctx, workqueue->wakeup_read_fd);
 }
 
+static void workqueue_orphan(grpc_exec_ctx *exec_ctx,
+                             grpc_workqueue *workqueue) {
+  if (gpr_atm_full_fetch_add(&workqueue->state, -1) == 1) {
+    workqueue_destroy(exec_ctx, workqueue);
+  }
+}
+
 #ifdef GRPC_WORKQUEUE_REFCOUNT_DEBUG
 void grpc_workqueue_ref(grpc_workqueue *workqueue, const char *file, int line,
                         const char *reason) {
+  if (workqueue == NULL) return;
   gpr_log(file, line, GPR_LOG_SEVERITY_DEBUG, "WORKQUEUE:%p   ref %d -> %d %s",
           workqueue, (int)workqueue->refs.count, (int)workqueue->refs.count + 1,
           reason);
-#else
-void grpc_workqueue_ref(grpc_workqueue *workqueue) {
-#endif
   gpr_ref(&workqueue->refs);
 }
+#else
+void grpc_workqueue_ref(grpc_workqueue *workqueue) {
+  if (workqueue == NULL) return;
+  gpr_ref(&workqueue->refs);
+}
+#endif
 
 #ifdef GRPC_WORKQUEUE_REFCOUNT_DEBUG
 void grpc_workqueue_unref(grpc_exec_ctx *exec_ctx, grpc_workqueue *workqueue,
                           const char *file, int line, const char *reason) {
+  if (workqueue == NULL) return;
   gpr_log(file, line, GPR_LOG_SEVERITY_DEBUG, "WORKQUEUE:%p unref %d -> %d %s",
           workqueue, (int)workqueue->refs.count, (int)workqueue->refs.count - 1,
           reason);
+  if (gpr_unref(&workqueue->refs)) {
+    workqueue_orphan(exec_ctx, workqueue);
+  }
+}
 #else
 void grpc_workqueue_unref(grpc_exec_ctx *exec_ctx, grpc_workqueue *workqueue) {
-#endif
+  if (workqueue == NULL) return;
   if (gpr_unref(&workqueue->refs)) {
-    workqueue_destroy(exec_ctx, workqueue);
+    workqueue_orphan(exec_ctx, workqueue);
+  }
+}
+#endif
+
+static void drain(grpc_exec_ctx *exec_ctx, grpc_workqueue *workqueue) {
+  abort();
+}
+
+static void wakeup(grpc_exec_ctx *exec_ctx, grpc_workqueue *workqueue) {
+  GPR_TIMER_MARK("workqueue.wakeup", 0);
+  grpc_error *err = grpc_wakeup_fd_wakeup(&workqueue->wakeup_fd);
+  if (!GRPC_LOG_IF_ERROR("wakeupfd_wakeup", err)) {
+    drain(exec_ctx, workqueue);
   }
 }
 
-void grpc_workqueue_flush(grpc_exec_ctx *exec_ctx, grpc_workqueue *workqueue) {
-  gpr_mu_lock(&workqueue->mu);
-  grpc_exec_ctx_enqueue_list(exec_ctx, &workqueue->closure_list, NULL);
-  gpr_mu_unlock(&workqueue->mu);
-}
-
 static void on_readable(grpc_exec_ctx *exec_ctx, void *arg, grpc_error *error) {
+  GPR_TIMER_BEGIN("workqueue.on_readable", 0);
+
   grpc_workqueue *workqueue = arg;
 
   if (error != GRPC_ERROR_NONE) {
-    gpr_mu_destroy(&workqueue->mu);
     /* HACK: let wakeup_fd code know that we stole the fd */
     workqueue->wakeup_fd.read_fd = 0;
     grpc_wakeup_fd_destroy(&workqueue->wakeup_fd);
     grpc_fd_orphan(exec_ctx, workqueue->wakeup_read_fd, NULL, NULL, "destroy");
+    GPR_ASSERT(gpr_atm_no_barrier_load(&workqueue->state) == 0);
     gpr_free(workqueue);
   } else {
-    gpr_mu_lock(&workqueue->mu);
-    grpc_exec_ctx_enqueue_list(exec_ctx, &workqueue->closure_list, NULL);
     error = grpc_wakeup_fd_consume_wakeup(&workqueue->wakeup_fd);
-    gpr_mu_unlock(&workqueue->mu);
+    gpr_mpscq_node *n = gpr_mpscq_pop(&workqueue->queue);
     if (error == GRPC_ERROR_NONE) {
       grpc_fd_notify_on_read(exec_ctx, workqueue->wakeup_read_fd,
                              &workqueue->read_closure);
@@ -128,24 +151,46 @@
       /* recurse to get error handling */
       on_readable(exec_ctx, arg, error);
     }
+    if (n == NULL) {
+      /* try again - queue in an inconsistant state */
+      wakeup(exec_ctx, workqueue);
+    } else {
+      switch (gpr_atm_full_fetch_add(&workqueue->state, -2)) {
+        case 3:  // had one count, one unorphaned --> done, unorphaned
+          break;
+        case 2:  // had one count, one orphaned --> done, orphaned
+          workqueue_destroy(exec_ctx, workqueue);
+          break;
+        case 1:
+        case 0:
+          // these values are illegal - representing an already done or
+          // deleted workqueue
+          GPR_UNREACHABLE_CODE(break);
+        default:
+          // schedule a wakeup since there's more to do
+          wakeup(exec_ctx, workqueue);
+      }
+      grpc_closure *cl = (grpc_closure *)n;
+      grpc_error *clerr = cl->error;
+      cl->cb(exec_ctx, cl->cb_arg, clerr);
+      GRPC_ERROR_UNREF(clerr);
+    }
   }
+
+  GPR_TIMER_END("workqueue.on_readable", 0);
 }
 
 void grpc_workqueue_enqueue(grpc_exec_ctx *exec_ctx, grpc_workqueue *workqueue,
                             grpc_closure *closure, grpc_error *error) {
-  grpc_error *push_error = GRPC_ERROR_NONE;
-  gpr_mu_lock(&workqueue->mu);
-  if (grpc_closure_list_empty(workqueue->closure_list)) {
-    push_error = grpc_wakeup_fd_wakeup(&workqueue->wakeup_fd);
+  GPR_TIMER_BEGIN("workqueue.enqueue", 0);
+  gpr_atm last = gpr_atm_full_fetch_add(&workqueue->state, 2);
+  GPR_ASSERT(last & 1);
+  closure->error = error;
+  gpr_mpscq_push(&workqueue->queue, &closure->next_data.atm_next);
+  if (last == 1) {
+    wakeup(exec_ctx, workqueue);
   }
-  grpc_closure_list_append(&workqueue->closure_list, closure, error);
-  if (push_error != GRPC_ERROR_NONE) {
-    const char *msg = grpc_error_string(push_error);
-    gpr_log(GPR_ERROR, "Failed to push to workqueue: %s", msg);
-    grpc_error_free_string(msg);
-    grpc_exec_ctx_enqueue_list(exec_ctx, &workqueue->closure_list, NULL);
-  }
-  gpr_mu_unlock(&workqueue->mu);
+  GPR_TIMER_END("workqueue.enqueue", 0);
 }
 
 #endif /* GPR_POSIX_SOCKET */
diff --git a/src/core/lib/iomgr/workqueue_posix.h b/src/core/lib/iomgr/workqueue_posix.h
index 0f26ba5..03ee21c 100644
--- a/src/core/lib/iomgr/workqueue_posix.h
+++ b/src/core/lib/iomgr/workqueue_posix.h
@@ -35,14 +35,17 @@
 #define GRPC_CORE_LIB_IOMGR_WORKQUEUE_POSIX_H
 
 #include "src/core/lib/iomgr/wakeup_fd_posix.h"
+#include "src/core/lib/support/mpscq.h"
 
 struct grpc_fd;
 
 struct grpc_workqueue {
   gpr_refcount refs;
-
-  gpr_mu mu;
-  grpc_closure_list closure_list;
+  gpr_mpscq queue;
+  // state is:
+  // lower bit - zero if orphaned
+  // other bits - number of items enqueued
+  gpr_atm state;
 
   grpc_wakeup_fd wakeup_fd;
   struct grpc_fd *wakeup_read_fd;
diff --git a/src/core/lib/iomgr/workqueue_windows.c b/src/core/lib/iomgr/workqueue_windows.c
index 23e2dea..ee81dc2 100644
--- a/src/core/lib/iomgr/workqueue_windows.c
+++ b/src/core/lib/iomgr/workqueue_windows.c
@@ -42,8 +42,6 @@
 // context, which is at least correct, if not performant or in the spirit of
 // workqueues.
 
-void grpc_workqueue_flush(grpc_exec_ctx *exec_ctx, grpc_workqueue *workqueue) {}
-
 #ifdef GRPC_WORKQUEUE_REFCOUNT_DEBUG
 void grpc_workqueue_ref(grpc_workqueue *workqueue, const char *file, int line,
                         const char *reason) {}
diff --git a/src/core/lib/security/credentials/plugin/plugin_credentials.c b/src/core/lib/security/credentials/plugin/plugin_credentials.c
index 824ff08..905de37 100644
--- a/src/core/lib/security/credentials/plugin/plugin_credentials.c
+++ b/src/core/lib/security/credentials/plugin/plugin_credentials.c
@@ -37,6 +37,7 @@
 
 #include "src/core/lib/surface/api_trace.h"
 
+#include <grpc/grpc.h>
 #include <grpc/support/alloc.h>
 #include <grpc/support/log.h>
 #include <grpc/support/string_util.h>
@@ -71,17 +72,33 @@
           error_details);
   } else {
     size_t i;
+    bool seen_illegal_header = false;
     grpc_credentials_md *md_array = NULL;
-    if (num_md > 0) {
+    for (i = 0; i < num_md; i++) {
+      if (!grpc_header_key_is_legal(md[i].key, strlen(md[i].key))) {
+        gpr_log(GPR_ERROR, "Plugin added invalid metadata key: %s", md[i].key);
+        seen_illegal_header = true;
+        break;
+      } else if (!grpc_is_binary_header(md[i].key, strlen(md[i].key)) &&
+                 !grpc_header_nonbin_value_is_legal(md[i].value,
+                                                    md[i].value_length)) {
+        gpr_log(GPR_ERROR, "Plugin added invalid metadata value.");
+        seen_illegal_header = true;
+        break;
+      }
+    }
+    if (seen_illegal_header) {
+      r->cb(&exec_ctx, r->user_data, NULL, 0, GRPC_CREDENTIALS_ERROR,
+            "Illegal metadata");
+    } else if (num_md > 0) {
       md_array = gpr_malloc(num_md * sizeof(grpc_credentials_md));
       for (i = 0; i < num_md; i++) {
         md_array[i].key = gpr_slice_from_copied_string(md[i].key);
         md_array[i].value =
             gpr_slice_from_copied_buffer(md[i].value, md[i].value_length);
       }
-    }
-    r->cb(&exec_ctx, r->user_data, md_array, num_md, GRPC_CREDENTIALS_OK, NULL);
-    if (md_array != NULL) {
+      r->cb(&exec_ctx, r->user_data, md_array, num_md, GRPC_CREDENTIALS_OK,
+            NULL);
       for (i = 0; i < num_md; i++) {
         gpr_slice_unref(md_array[i].key);
         gpr_slice_unref(md_array[i].value);
diff --git a/src/core/lib/security/transport/client_auth_filter.c b/src/core/lib/security/transport/client_auth_filter.c
index 2a1bf4d..b366d14 100644
--- a/src/core/lib/security/transport/client_auth_filter.c
+++ b/src/core/lib/security/transport/client_auth_filter.c
@@ -40,6 +40,7 @@
 #include <grpc/support/string_util.h>
 
 #include "src/core/lib/channel/channel_stack.h"
+#include "src/core/lib/profiling/timers.h"
 #include "src/core/lib/security/context/security_context.h"
 #include "src/core/lib/security/credentials/credentials.h"
 #include "src/core/lib/security/transport/security_connector.h"
@@ -218,6 +219,8 @@
 static void auth_start_transport_op(grpc_exec_ctx *exec_ctx,
                                     grpc_call_element *elem,
                                     grpc_transport_stream_op *op) {
+  GPR_TIMER_BEGIN("auth_start_transport_op", 0);
+
   /* grab pointers to our data from the call element */
   call_data *calld = elem->call_data;
   channel_data *chand = elem->channel_data;
@@ -258,12 +261,14 @@
       grpc_channel_security_connector_check_call_host(
           exec_ctx, chand->security_connector, call_host, chand->auth_context,
           on_host_checked, elem);
+      GPR_TIMER_END("auth_start_transport_op", 0);
       return; /* early exit */
     }
   }
 
   /* pass control down the stack */
   grpc_call_next_op(exec_ctx, elem, op);
+  GPR_TIMER_END("auth_start_transport_op", 0);
 }
 
 /* Constructor for call_data */
diff --git a/src/core/lib/security/transport/secure_endpoint.c b/src/core/lib/security/transport/secure_endpoint.c
index 0169ccd..acb0113 100644
--- a/src/core/lib/security/transport/secure_endpoint.c
+++ b/src/core/lib/security/transport/secure_endpoint.c
@@ -38,6 +38,7 @@
 #include <grpc/support/slice_buffer.h>
 #include <grpc/support/sync.h>
 #include "src/core/lib/debug/trace.h"
+#include "src/core/lib/profiling/timers.h"
 #include "src/core/lib/security/transport/tsi_error.h"
 #include "src/core/lib/support/string.h"
 #include "src/core/lib/tsi/transport_security_interface.h"
@@ -248,6 +249,8 @@
 
 static void endpoint_write(grpc_exec_ctx *exec_ctx, grpc_endpoint *secure_ep,
                            gpr_slice_buffer *slices, grpc_closure *cb) {
+  GPR_TIMER_BEGIN("secure_endpoint.endpoint_write", 0);
+
   unsigned i;
   tsi_result result = TSI_OK;
   secure_endpoint *ep = (secure_endpoint *)secure_ep;
@@ -323,10 +326,12 @@
         exec_ctx, cb,
         grpc_set_tsi_error_result(GRPC_ERROR_CREATE("Wrap failed"), result),
         NULL);
+    GPR_TIMER_END("secure_endpoint.endpoint_write", 0);
     return;
   }
 
   grpc_endpoint_write(exec_ctx, ep->wrapped_ep, &ep->output_buffer, cb);
+  GPR_TIMER_END("secure_endpoint.endpoint_write", 0);
 }
 
 static void endpoint_shutdown(grpc_exec_ctx *exec_ctx,
diff --git a/src/core/lib/security/transport/server_auth_filter.c b/src/core/lib/security/transport/server_auth_filter.c
index def16c8..b2c6815 100644
--- a/src/core/lib/security/transport/server_auth_filter.c
+++ b/src/core/lib/security/transport/server_auth_filter.c
@@ -48,7 +48,7 @@
      up-call on transport_op, and remember to call our on_done_recv member after
      handling it. */
   grpc_closure auth_on_recv;
-  grpc_transport_stream_op transport_op;
+  grpc_transport_stream_op *transport_op;
   grpc_metadata_array md;
   const grpc_metadata *consumed_md;
   size_t num_consumed_md;
@@ -106,6 +106,10 @@
   return md;
 }
 
+static void destroy_op(grpc_exec_ctx *exec_ctx, void *arg, grpc_error *error) {
+  gpr_free(arg);
+}
+
 /* called from application code */
 static void on_md_processing_done(
     void *user_data, const grpc_metadata *consumed_md, size_t num_consumed_md,
@@ -131,21 +135,22 @@
     grpc_exec_ctx_sched(&exec_ctx, calld->on_done_recv, GRPC_ERROR_NONE, NULL);
   } else {
     gpr_slice message;
-    grpc_transport_stream_op close_op;
-    memset(&close_op, 0, sizeof(close_op));
+    grpc_transport_stream_op *close_op = gpr_malloc(sizeof(*close_op));
+    memset(close_op, 0, sizeof(*close_op));
     grpc_metadata_array_destroy(&calld->md);
     error_details = error_details != NULL
                         ? error_details
                         : "Authentication metadata processing failed.";
     message = gpr_slice_from_copied_string(error_details);
-    calld->transport_op.send_initial_metadata = NULL;
-    if (calld->transport_op.send_message != NULL) {
-      grpc_byte_stream_destroy(&exec_ctx, calld->transport_op.send_message);
-      calld->transport_op.send_message = NULL;
+    calld->transport_op->send_initial_metadata = NULL;
+    if (calld->transport_op->send_message != NULL) {
+      grpc_byte_stream_destroy(&exec_ctx, calld->transport_op->send_message);
+      calld->transport_op->send_message = NULL;
     }
-    calld->transport_op.send_trailing_metadata = NULL;
-    grpc_transport_stream_op_add_close(&close_op, status, &message);
-    grpc_call_next_op(&exec_ctx, elem, &close_op);
+    calld->transport_op->send_trailing_metadata = NULL;
+    close_op->on_complete = grpc_closure_create(destroy_op, close_op);
+    grpc_transport_stream_op_add_close(close_op, status, &message);
+    grpc_call_next_op(&exec_ctx, elem, close_op);
     grpc_exec_ctx_sched(&exec_ctx, calld->on_done_recv,
                         grpc_error_set_int(GRPC_ERROR_CREATE(error_details),
                                            GRPC_ERROR_INT_GRPC_STATUS, status),
@@ -182,7 +187,7 @@
     calld->recv_initial_metadata = op->recv_initial_metadata;
     calld->on_done_recv = op->recv_initial_metadata_ready;
     op->recv_initial_metadata_ready = &calld->auth_on_recv;
-    calld->transport_op = *op;
+    calld->transport_op = op;
   }
 }
 
diff --git a/src/core/lib/support/mpscq.c b/src/core/lib/support/mpscq.c
new file mode 100644
index 0000000..5b93232
--- /dev/null
+++ b/src/core/lib/support/mpscq.c
@@ -0,0 +1,83 @@
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include "src/core/lib/support/mpscq.h"
+
+#include <grpc/support/log.h>
+
+void gpr_mpscq_init(gpr_mpscq *q) {
+  gpr_atm_no_barrier_store(&q->head, (gpr_atm)&q->stub);
+  q->tail = &q->stub;
+  gpr_atm_no_barrier_store(&q->stub.next, (gpr_atm)NULL);
+}
+
+void gpr_mpscq_destroy(gpr_mpscq *q) {
+  GPR_ASSERT(gpr_atm_no_barrier_load(&q->head) == (gpr_atm)&q->stub);
+  GPR_ASSERT(q->tail == &q->stub);
+}
+
+void gpr_mpscq_push(gpr_mpscq *q, gpr_mpscq_node *n) {
+  gpr_atm_no_barrier_store(&n->next, (gpr_atm)NULL);
+  gpr_mpscq_node *prev =
+      (gpr_mpscq_node *)gpr_atm_full_xchg(&q->head, (gpr_atm)n);
+  gpr_atm_rel_store(&prev->next, (gpr_atm)n);
+}
+
+gpr_mpscq_node *gpr_mpscq_pop(gpr_mpscq *q) {
+  gpr_mpscq_node *tail = q->tail;
+  gpr_mpscq_node *next = (gpr_mpscq_node *)gpr_atm_acq_load(&tail->next);
+  if (tail == &q->stub) {
+    // indicates the list is actually (ephemerally) empty
+    if (next == NULL) return NULL;
+    q->tail = next;
+    tail = next;
+    next = (gpr_mpscq_node *)gpr_atm_acq_load(&tail->next);
+  }
+  if (next != NULL) {
+    q->tail = next;
+    return tail;
+  }
+  gpr_mpscq_node *head = (gpr_mpscq_node *)gpr_atm_acq_load(&q->head);
+  if (tail != head) {
+    // indicates a retry is in order: we're still adding
+    return NULL;
+  }
+  gpr_mpscq_push(q, &q->stub);
+  next = (gpr_mpscq_node *)gpr_atm_acq_load(&tail->next);
+  if (next != NULL) {
+    q->tail = next;
+    return tail;
+  }
+  // indicates a retry is in order: we're still adding
+  return NULL;
+}
diff --git a/src/core/lib/support/mpscq.h b/src/core/lib/support/mpscq.h
new file mode 100644
index 0000000..977a117
--- /dev/null
+++ b/src/core/lib/support/mpscq.h
@@ -0,0 +1,65 @@
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifndef GRPC_CORE_LIB_SUPPORT_MPSCQ_H
+#define GRPC_CORE_LIB_SUPPORT_MPSCQ_H
+
+#include <grpc/support/atm.h>
+#include <stddef.h>
+
+// Multiple-producer single-consumer lock free queue, based upon the
+// implementation from Dmitry Vyukov here:
+// http://www.1024cores.net/home/lock-free-algorithms/queues/intrusive-mpsc-node-based-queue
+
+// List node (include this in a data structure at the top, and add application
+// fields after it - to simulate inheritance)
+typedef struct gpr_mpscq_node { gpr_atm next; } gpr_mpscq_node;
+
+// Actual queue type
+typedef struct gpr_mpscq {
+  gpr_atm head;
+  // make sure head & tail don't share a cacheline
+  char padding[GPR_CACHELINE_SIZE];
+  gpr_mpscq_node *tail;
+  gpr_mpscq_node stub;
+} gpr_mpscq;
+
+void gpr_mpscq_init(gpr_mpscq *q);
+void gpr_mpscq_destroy(gpr_mpscq *q);
+// Push a node
+void gpr_mpscq_push(gpr_mpscq *q, gpr_mpscq_node *n);
+// Pop a node (returns NULL if no node is ready - which doesn't indicate that
+// the queue is empty!!)
+gpr_mpscq_node *gpr_mpscq_pop(gpr_mpscq *q);
+
+#endif /* GRPC_CORE_LIB_SUPPORT_MPSCQ_H */
diff --git a/src/core/lib/surface/call.c b/src/core/lib/surface/call.c
index 7726811..119f5e8 100644
--- a/src/core/lib/surface/call.c
+++ b/src/core/lib/surface/call.c
@@ -109,6 +109,10 @@
   uint8_t recv_message;
   uint8_t recv_final_op;
   uint8_t is_notify_tag_closure;
+
+  /* TODO(ctiller): now that this is inlined, figure out how much of the above
+                    state can be eliminated */
+  grpc_transport_stream_op op;
 } batch_control;
 
 struct grpc_call {
@@ -778,6 +782,7 @@
   grpc_error *error;
   grpc_closure *op_closure;
   enum { TC_CANCEL, TC_CLOSE } type;
+  grpc_transport_stream_op op;
 } termination_closure;
 
 static void done_termination(grpc_exec_ctx *exec_ctx, void *tcp,
@@ -797,26 +802,24 @@
 }
 
 static void send_cancel(grpc_exec_ctx *exec_ctx, void *tcp, grpc_error *error) {
-  grpc_transport_stream_op op;
   termination_closure *tc = tcp;
-  memset(&op, 0, sizeof(op));
-  op.cancel_error = tc->error;
+  memset(&tc->op, 0, sizeof(tc->op));
+  tc->op.cancel_error = tc->error;
   /* reuse closure to catch completion */
   grpc_closure_init(&tc->closure, done_termination, tc);
-  op.on_complete = &tc->closure;
-  execute_op(exec_ctx, tc->call, &op);
+  tc->op.on_complete = &tc->closure;
+  execute_op(exec_ctx, tc->call, &tc->op);
 }
 
 static void send_close(grpc_exec_ctx *exec_ctx, void *tcp, grpc_error *error) {
-  grpc_transport_stream_op op;
   termination_closure *tc = tcp;
-  memset(&op, 0, sizeof(op));
-  op.close_error = tc->error;
+  memset(&tc->op, 0, sizeof(tc->op));
+  tc->op.close_error = tc->error;
   /* reuse closure to catch completion */
   grpc_closure_init(&tc->closure, done_termination, tc);
-  tc->op_closure = op.on_complete;
-  op.on_complete = &tc->closure;
-  execute_op(exec_ctx, tc->call, &op);
+  tc->op_closure = tc->op.on_complete;
+  tc->op.on_complete = &tc->closure;
+  execute_op(exec_ctx, tc->call, &tc->op);
 }
 
 static grpc_call_error terminate_with_status(grpc_exec_ctx *exec_ctx,
@@ -1370,7 +1373,6 @@
                                         grpc_call *call, const grpc_op *ops,
                                         size_t nops, void *notify_tag,
                                         int is_notify_tag_closure) {
-  grpc_transport_stream_op stream_op;
   size_t i;
   const grpc_op *op;
   batch_control *bctl;
@@ -1384,8 +1386,6 @@
 
   GRPC_CALL_LOG_BATCH(GPR_INFO, call, ops, nops, notify_tag);
 
-  memset(&stream_op, 0, sizeof(stream_op));
-
   /* TODO(ctiller): this feels like it could be made lock-free */
   gpr_mu_lock(&call->mu);
   bctl = allocate_batch_control(call);
@@ -1394,6 +1394,9 @@
   bctl->notify_tag = notify_tag;
   bctl->is_notify_tag_closure = (uint8_t)(is_notify_tag_closure != 0);
 
+  grpc_transport_stream_op *stream_op = &bctl->op;
+  memset(stream_op, 0, sizeof(*stream_op));
+
   if (nops == 0) {
     GRPC_CALL_INTERNAL_REF(call, "completion");
     bctl->error = GRPC_ERROR_NONE;
@@ -1471,9 +1474,9 @@
         }
         /* TODO(ctiller): just make these the same variable? */
         call->metadata_batch[0][0].deadline = call->send_deadline;
-        stream_op.send_initial_metadata =
+        stream_op->send_initial_metadata =
             &call->metadata_batch[0 /* is_receiving */][0 /* is_trailing */];
-        stream_op.send_initial_metadata_flags = op->flags;
+        stream_op->send_initial_metadata_flags = op->flags;
         break;
       case GRPC_OP_SEND_MESSAGE:
         if (!are_write_flags_valid(op->flags)) {
@@ -1493,7 +1496,7 @@
         grpc_slice_buffer_stream_init(
             &call->sending_stream,
             &op->data.send_message->data.raw.slice_buffer, op->flags);
-        stream_op.send_message = &call->sending_stream.base;
+        stream_op->send_message = &call->sending_stream.base;
         break;
       case GRPC_OP_SEND_CLOSE_FROM_CLIENT:
         /* Flag validation: currently allow no flags */
@@ -1511,7 +1514,7 @@
         }
         bctl->send_final_op = 1;
         call->sent_final_op = 1;
-        stream_op.send_trailing_metadata =
+        stream_op->send_trailing_metadata =
             &call->metadata_batch[0 /* is_receiving */][1 /* is_trailing */];
         break;
       case GRPC_OP_SEND_STATUS_FROM_SERVER:
@@ -1558,7 +1561,7 @@
           error = GRPC_CALL_ERROR_INVALID_METADATA;
           goto done_with_error;
         }
-        stream_op.send_trailing_metadata =
+        stream_op->send_trailing_metadata =
             &call->metadata_batch[0 /* is_receiving */][1 /* is_trailing */];
         break;
       case GRPC_OP_RECV_INITIAL_METADATA:
@@ -1576,9 +1579,9 @@
         grpc_closure_init(&call->receiving_initial_metadata_ready,
                           receiving_initial_metadata_ready, bctl);
         bctl->recv_initial_metadata = 1;
-        stream_op.recv_initial_metadata =
+        stream_op->recv_initial_metadata =
             &call->metadata_batch[1 /* is_receiving */][0 /* is_trailing */];
-        stream_op.recv_initial_metadata_ready =
+        stream_op->recv_initial_metadata_ready =
             &call->receiving_initial_metadata_ready;
         num_completion_callbacks_needed++;
         break;
@@ -1595,10 +1598,10 @@
         call->receiving_message = 1;
         bctl->recv_message = 1;
         call->receiving_buffer = op->data.recv_message;
-        stream_op.recv_message = &call->receiving_stream;
+        stream_op->recv_message = &call->receiving_stream;
         grpc_closure_init(&call->receiving_stream_ready, receiving_stream_ready,
                           bctl);
-        stream_op.recv_message_ready = &call->receiving_stream_ready;
+        stream_op->recv_message_ready = &call->receiving_stream_ready;
         num_completion_callbacks_needed++;
         break;
       case GRPC_OP_RECV_STATUS_ON_CLIENT:
@@ -1624,9 +1627,9 @@
         call->final_op.client.status_details_capacity =
             op->data.recv_status_on_client.status_details_capacity;
         bctl->recv_final_op = 1;
-        stream_op.recv_trailing_metadata =
+        stream_op->recv_trailing_metadata =
             &call->metadata_batch[1 /* is_receiving */][1 /* is_trailing */];
-        stream_op.collect_stats =
+        stream_op->collect_stats =
             &call->final_info.stats.transport_stream_stats;
         break;
       case GRPC_OP_RECV_CLOSE_ON_SERVER:
@@ -1647,9 +1650,9 @@
         call->final_op.server.cancelled =
             op->data.recv_close_on_server.cancelled;
         bctl->recv_final_op = 1;
-        stream_op.recv_trailing_metadata =
+        stream_op->recv_trailing_metadata =
             &call->metadata_batch[1 /* is_receiving */][1 /* is_trailing */];
-        stream_op.collect_stats =
+        stream_op->collect_stats =
             &call->final_info.stats.transport_stream_stats;
         break;
     }
@@ -1661,12 +1664,12 @@
   }
   gpr_ref_init(&bctl->steps_to_complete, num_completion_callbacks_needed);
 
-  stream_op.context = call->context;
+  stream_op->context = call->context;
   grpc_closure_init(&bctl->finish_batch, finish_batch, bctl);
-  stream_op.on_complete = &bctl->finish_batch;
+  stream_op->on_complete = &bctl->finish_batch;
   gpr_mu_unlock(&call->mu);
 
-  execute_op(exec_ctx, call, &stream_op);
+  execute_op(exec_ctx, call, stream_op);
 
 done:
   GPR_TIMER_END("grpc_call_start_batch", 0);
diff --git a/src/core/lib/surface/channel.c b/src/core/lib/surface/channel.c
index 6d2b1c4..52e7856 100644
--- a/src/core/lib/surface/channel.c
+++ b/src/core/lib/surface/channel.c
@@ -334,14 +334,13 @@
 }
 
 void grpc_channel_destroy(grpc_channel *channel) {
-  grpc_transport_op op;
+  grpc_transport_op *op = grpc_make_transport_op(NULL);
   grpc_channel_element *elem;
   grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
   GRPC_API_TRACE("grpc_channel_destroy(channel=%p)", 1, (channel));
-  memset(&op, 0, sizeof(op));
-  op.disconnect_with_error = GRPC_ERROR_CREATE("Channel Destroyed");
+  op->disconnect_with_error = GRPC_ERROR_CREATE("Channel Destroyed");
   elem = grpc_channel_stack_element(CHANNEL_STACK_FROM_CHANNEL(channel), 0);
-  elem->filter->start_transport_op(&exec_ctx, elem, &op);
+  elem->filter->start_transport_op(&exec_ctx, elem, op);
 
   GRPC_CHANNEL_INTERNAL_UNREF(&exec_ctx, channel, "channel");
 
diff --git a/src/core/lib/surface/channel_ping.c b/src/core/lib/surface/channel_ping.c
index 9818f9d..0d2f01a 100644
--- a/src/core/lib/surface/channel_ping.c
+++ b/src/core/lib/surface/channel_ping.c
@@ -61,19 +61,20 @@
 
 void grpc_channel_ping(grpc_channel *channel, grpc_completion_queue *cq,
                        void *tag, void *reserved) {
-  grpc_transport_op op;
+  GRPC_API_TRACE("grpc_channel_ping(channel=%p, cq=%p, tag=%p, reserved=%p)", 4,
+                 (channel, cq, tag, reserved));
+  grpc_transport_op *op = grpc_make_transport_op(NULL);
   ping_result *pr = gpr_malloc(sizeof(*pr));
   grpc_channel_element *top_elem =
       grpc_channel_stack_element(grpc_channel_get_channel_stack(channel), 0);
   grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
   GPR_ASSERT(reserved == NULL);
-  memset(&op, 0, sizeof(op));
   pr->tag = tag;
   pr->cq = cq;
   grpc_closure_init(&pr->closure, ping_done, pr);
-  op.send_ping = &pr->closure;
-  op.bind_pollset = grpc_cq_pollset(cq);
+  op->send_ping = &pr->closure;
+  op->bind_pollset = grpc_cq_pollset(cq);
   grpc_cq_begin_op(cq, tag);
-  top_elem->filter->start_transport_op(&exec_ctx, top_elem, &op);
+  top_elem->filter->start_transport_op(&exec_ctx, top_elem, op);
   grpc_exec_ctx_finish(&exec_ctx);
 }
diff --git a/src/core/lib/surface/init.c b/src/core/lib/surface/init.c
index 5397913..edda0c8 100644
--- a/src/core/lib/surface/init.c
+++ b/src/core/lib/surface/init.c
@@ -47,6 +47,7 @@
 #include "src/core/lib/channel/http_server_filter.h"
 #include "src/core/lib/debug/trace.h"
 #include "src/core/lib/http/parser.h"
+#include "src/core/lib/iomgr/combiner.h"
 #include "src/core/lib/iomgr/executor.h"
 #include "src/core/lib/iomgr/iomgr.h"
 #include "src/core/lib/profiling/timers.h"
@@ -165,6 +166,7 @@
     grpc_register_tracer("http1", &grpc_http1_trace);
     grpc_register_tracer("compression", &grpc_compression_trace);
     grpc_register_tracer("queue_pluck", &grpc_cq_pluck_trace);
+    grpc_register_tracer("combiner", &grpc_combiner_trace);
     // Default pluck trace to 1
     grpc_cq_pluck_trace = 1;
     grpc_register_tracer("queue_timeout", &grpc_cq_event_timeout_trace);
diff --git a/src/core/lib/surface/lame_client.c b/src/core/lib/surface/lame_client.c
index 19b7836..d32c884 100644
--- a/src/core/lib/surface/lame_client.c
+++ b/src/core/lib/surface/lame_client.c
@@ -97,14 +97,14 @@
     grpc_exec_ctx_sched(exec_ctx, op->on_connectivity_state_change,
                         GRPC_ERROR_NONE, NULL);
   }
-  if (op->on_consumed != NULL) {
-    grpc_exec_ctx_sched(exec_ctx, op->on_consumed, GRPC_ERROR_NONE, NULL);
-  }
   if (op->send_ping != NULL) {
     grpc_exec_ctx_sched(exec_ctx, op->send_ping,
                         GRPC_ERROR_CREATE("lame client channel"), NULL);
   }
   GRPC_ERROR_UNREF(op->disconnect_with_error);
+  if (op->on_consumed != NULL) {
+    grpc_exec_ctx_sched(exec_ctx, op->on_consumed, GRPC_ERROR_NONE, NULL);
+  }
 }
 
 static grpc_error *init_call_elem(grpc_exec_ctx *exec_ctx,
diff --git a/src/core/lib/surface/server.c b/src/core/lib/surface/server.c
index 55e6d99..56fb80e 100644
--- a/src/core/lib/surface/server.c
+++ b/src/core/lib/surface/server.c
@@ -273,23 +273,20 @@
 }
 
 static void send_shutdown(grpc_exec_ctx *exec_ctx, grpc_channel *channel,
-                          bool send_goaway, grpc_error *send_disconnect) {
-  grpc_transport_op op;
-  struct shutdown_cleanup_args *sc;
+                          int send_goaway, grpc_error *send_disconnect) {
+  struct shutdown_cleanup_args *sc = gpr_malloc(sizeof(*sc));
+  grpc_closure_init(&sc->closure, shutdown_cleanup, sc);
+  grpc_transport_op *op = grpc_make_transport_op(&sc->closure);
   grpc_channel_element *elem;
 
-  memset(&op, 0, sizeof(op));
-  op.send_goaway = send_goaway;
-  sc = gpr_malloc(sizeof(*sc));
+  op->send_goaway = send_goaway;
   sc->slice = gpr_slice_from_copied_string("Server shutdown");
-  op.goaway_message = &sc->slice;
-  op.goaway_status = GRPC_STATUS_OK;
-  op.disconnect_with_error = send_disconnect;
-  grpc_closure_init(&sc->closure, shutdown_cleanup, sc);
-  op.on_consumed = &sc->closure;
+  op->goaway_message = &sc->slice;
+  op->goaway_status = GRPC_STATUS_OK;
+  op->disconnect_with_error = send_disconnect;
 
   elem = grpc_channel_stack_element(grpc_channel_get_channel_stack(channel), 0);
-  elem->filter->start_transport_op(exec_ctx, elem, &op);
+  elem->filter->start_transport_op(exec_ctx, elem, op);
 }
 
 static void channel_broadcaster_shutdown(grpc_exec_ctx *exec_ctx,
@@ -432,7 +429,8 @@
   server_unref(exec_ctx, server);
 }
 
-static void destroy_channel(grpc_exec_ctx *exec_ctx, channel_data *chand) {
+static void destroy_channel(grpc_exec_ctx *exec_ctx, channel_data *chand,
+                            grpc_error *error) {
   if (is_channel_orphaned(chand)) return;
   GPR_ASSERT(chand->server != NULL);
   orphan_channel(chand);
@@ -441,14 +439,20 @@
   chand->finish_destroy_channel_closure.cb = finish_destroy_channel;
   chand->finish_destroy_channel_closure.cb_arg = chand;
 
-  grpc_transport_op op;
-  memset(&op, 0, sizeof(op));
-  op.set_accept_stream = true;
-  op.on_consumed = &chand->finish_destroy_channel_closure;
+  grpc_transport_op *op =
+      grpc_make_transport_op(&chand->finish_destroy_channel_closure);
+  op->set_accept_stream = true;
   grpc_channel_next_op(exec_ctx,
                        grpc_channel_stack_element(
                            grpc_channel_get_channel_stack(chand->channel), 0),
-                       &op);
+                       op);
+
+  if (error != GRPC_ERROR_NONE) {
+    const char *msg = grpc_error_string(error);
+    gpr_log(GPR_INFO, "Disconnected client: %s", msg);
+    grpc_error_free_string(msg);
+  }
+  GRPC_ERROR_UNREF(error);
 }
 
 static void cpstr(char **dest, size_t *capacity, grpc_mdstr *value) {
@@ -845,17 +849,16 @@
   channel_data *chand = cd;
   grpc_server *server = chand->server;
   if (chand->connectivity_state != GRPC_CHANNEL_SHUTDOWN) {
-    grpc_transport_op op;
-    memset(&op, 0, sizeof(op));
-    op.on_connectivity_state_change = &chand->channel_connectivity_changed,
-    op.connectivity_state = &chand->connectivity_state;
+    grpc_transport_op *op = grpc_make_transport_op(NULL);
+    op->on_connectivity_state_change = &chand->channel_connectivity_changed,
+    op->connectivity_state = &chand->connectivity_state;
     grpc_channel_next_op(exec_ctx,
                          grpc_channel_stack_element(
                              grpc_channel_get_channel_stack(chand->channel), 0),
-                         &op);
+                         op);
   } else {
     gpr_mu_lock(&server->mu_global);
-    destroy_channel(exec_ctx, chand);
+    destroy_channel(exec_ctx, chand, GRPC_ERROR_REF(error));
     gpr_mu_unlock(&server->mu_global);
     GRPC_CHANNEL_INTERNAL_UNREF(exec_ctx, chand->channel, "connectivity");
   }
@@ -1119,7 +1122,7 @@
   size_t slots;
   uint32_t probes;
   uint32_t max_probes = 0;
-  grpc_transport_op op;
+  grpc_transport_op *op = NULL;
 
   channel =
       grpc_channel_create(exec_ctx, NULL, args, GRPC_SERVER_CHANNEL, transport);
@@ -1179,16 +1182,16 @@
   gpr_mu_unlock(&s->mu_global);
 
   GRPC_CHANNEL_INTERNAL_REF(channel, "connectivity");
-  memset(&op, 0, sizeof(op));
-  op.set_accept_stream = true;
-  op.set_accept_stream_fn = accept_stream;
-  op.set_accept_stream_user_data = chand;
-  op.on_connectivity_state_change = &chand->channel_connectivity_changed;
-  op.connectivity_state = &chand->connectivity_state;
+  op = grpc_make_transport_op(NULL);
+  op->set_accept_stream = true;
+  op->set_accept_stream_fn = accept_stream;
+  op->set_accept_stream_user_data = chand;
+  op->on_connectivity_state_change = &chand->channel_connectivity_changed;
+  op->connectivity_state = &chand->connectivity_state;
   if (gpr_atm_acq_load(&s->shutdown_flag) != 0) {
-    op.disconnect_with_error = GRPC_ERROR_CREATE("Server shutdown");
+    op->disconnect_with_error = GRPC_ERROR_CREATE("Server shutdown");
   }
-  grpc_transport_perform_op(exec_ctx, transport, &op);
+  grpc_transport_perform_op(exec_ctx, transport, op);
 }
 
 void done_published_shutdown(grpc_exec_ctx *exec_ctx, void *done_arg,
diff --git a/src/core/lib/transport/metadata.c b/src/core/lib/transport/metadata.c
index 0677f29..4b40c27 100644
--- a/src/core/lib/transport/metadata.c
+++ b/src/core/lib/transport/metadata.c
@@ -278,7 +278,7 @@
                           internal_metadata *md DEBUG_ARGS) {
 #ifdef GRPC_METADATA_REFCOUNT_DEBUG
   gpr_log(file, line, GPR_LOG_SEVERITY_DEBUG,
-          "ELM   REF:%p:%d->%d: '%s' = '%s'", md,
+          "ELM   REF:%p:%zu->%zu: '%s' = '%s'", (void *)md,
           gpr_atm_no_barrier_load(&md->refcnt),
           gpr_atm_no_barrier_load(&md->refcnt) + 1,
           grpc_mdstr_as_c_string((grpc_mdstr *)md->key),
@@ -566,7 +566,7 @@
   shard->elems[idx] = md;
   gpr_mu_init(&md->mu_user_data);
 #ifdef GRPC_METADATA_REFCOUNT_DEBUG
-  gpr_log(GPR_DEBUG, "ELM   NEW:%p:%d: '%s' = '%s'", md,
+  gpr_log(GPR_DEBUG, "ELM   NEW:%p:%zu: '%s' = '%s'", (void *)md,
           gpr_atm_no_barrier_load(&md->refcnt),
           grpc_mdstr_as_c_string((grpc_mdstr *)md->key),
           grpc_mdstr_as_c_string((grpc_mdstr *)md->value));
@@ -639,7 +639,7 @@
   if (is_mdelem_static(gmd)) return gmd;
 #ifdef GRPC_METADATA_REFCOUNT_DEBUG
   gpr_log(file, line, GPR_LOG_SEVERITY_DEBUG,
-          "ELM   REF:%p:%d->%d: '%s' = '%s'", md,
+          "ELM   REF:%p:%zu->%zu: '%s' = '%s'", (void *)md,
           gpr_atm_no_barrier_load(&md->refcnt),
           gpr_atm_no_barrier_load(&md->refcnt) + 1,
           grpc_mdstr_as_c_string((grpc_mdstr *)md->key),
@@ -649,7 +649,7 @@
      this function - meaning that no adjustment to mdtab_free is necessary,
      simplifying the logic here to be just an atomic increment */
   /* use C assert to have this removed in opt builds */
-  assert(gpr_atm_no_barrier_load(&md->refcnt) >= 1);
+  GPR_ASSERT(gpr_atm_no_barrier_load(&md->refcnt) >= 1);
   gpr_atm_no_barrier_fetch_add(&md->refcnt, 1);
   return gmd;
 }
@@ -660,14 +660,16 @@
   if (is_mdelem_static(gmd)) return;
 #ifdef GRPC_METADATA_REFCOUNT_DEBUG
   gpr_log(file, line, GPR_LOG_SEVERITY_DEBUG,
-          "ELM UNREF:%p:%d->%d: '%s' = '%s'", md,
+          "ELM UNREF:%p:%zu->%zu: '%s' = '%s'", (void *)md,
           gpr_atm_no_barrier_load(&md->refcnt),
           gpr_atm_no_barrier_load(&md->refcnt) - 1,
           grpc_mdstr_as_c_string((grpc_mdstr *)md->key),
           grpc_mdstr_as_c_string((grpc_mdstr *)md->value));
 #endif
   uint32_t hash = GRPC_MDSTR_KV_HASH(md->key->hash, md->value->hash);
-  if (1 == gpr_atm_full_fetch_add(&md->refcnt, -1)) {
+  const gpr_atm prev_refcount = gpr_atm_full_fetch_add(&md->refcnt, -1);
+  GPR_ASSERT(prev_refcount >= 1);
+  if (1 == prev_refcount) {
     /* once the refcount hits zero, some other thread can come along and
        free md at any time: it's unsafe from this point on to access it */
     mdtab_shard *shard =
@@ -676,10 +678,12 @@
   }
 }
 
-const char *grpc_mdstr_as_c_string(grpc_mdstr *s) {
+const char *grpc_mdstr_as_c_string(const grpc_mdstr *s) {
   return (const char *)GPR_SLICE_START_PTR(s->slice);
 }
 
+size_t grpc_mdstr_length(const grpc_mdstr *s) { return GRPC_MDSTR_LENGTH(s); }
+
 grpc_mdstr *grpc_mdstr_ref(grpc_mdstr *gs DEBUG_ARGS) {
   internal_string *s = (internal_string *)gs;
   if (is_mdstr_static(gs)) return gs;
diff --git a/src/core/lib/transport/metadata.h b/src/core/lib/transport/metadata.h
index 2b0921c..71eff0a 100644
--- a/src/core/lib/transport/metadata.h
+++ b/src/core/lib/transport/metadata.h
@@ -147,7 +147,7 @@
 
 /* Recover a char* from a grpc_mdstr. The returned string is null terminated.
    Does not promise that the returned string has no embedded nulls however. */
-const char *grpc_mdstr_as_c_string(grpc_mdstr *s);
+const char *grpc_mdstr_as_c_string(const grpc_mdstr *s);
 
 #define GRPC_MDSTR_LENGTH(s) (GPR_SLICE_LENGTH(s->slice))
 
diff --git a/src/core/lib/transport/transport.c b/src/core/lib/transport/transport.c
index 857c390..08f9d7e 100644
--- a/src/core/lib/transport/transport.c
+++ b/src/core/lib/transport/transport.c
@@ -32,10 +32,14 @@
  */
 
 #include "src/core/lib/transport/transport.h"
+
+#include <string.h>
+
 #include <grpc/support/alloc.h>
 #include <grpc/support/atm.h>
 #include <grpc/support/log.h>
 #include <grpc/support/sync.h>
+
 #include "src/core/lib/support/string.h"
 #include "src/core/lib/transport/transport_impl.h"
 
@@ -247,3 +251,26 @@
   error = grpc_error_set_int(error, GRPC_ERROR_INT_GRPC_STATUS, status);
   add_error(op, &op->close_error, error);
 }
+
+typedef struct {
+  grpc_closure outer_on_complete;
+  grpc_closure *inner_on_complete;
+  grpc_transport_op op;
+} made_transport_op;
+
+static void destroy_made_transport_op(grpc_exec_ctx *exec_ctx, void *arg,
+                                      grpc_error *error) {
+  made_transport_op *op = arg;
+  grpc_exec_ctx_sched(exec_ctx, op->inner_on_complete, GRPC_ERROR_REF(error),
+                      NULL);
+  gpr_free(op);
+}
+
+grpc_transport_op *grpc_make_transport_op(grpc_closure *on_complete) {
+  made_transport_op *op = gpr_malloc(sizeof(*op));
+  grpc_closure_init(&op->outer_on_complete, destroy_made_transport_op, op);
+  op->inner_on_complete = on_complete;
+  memset(&op->op, 0, sizeof(op->op));
+  op->op.on_consumed = &op->outer_on_complete;
+  return &op->op;
+}
diff --git a/src/core/lib/transport/transport.h b/src/core/lib/transport/transport.h
index 26ed6cb..8dc393f 100644
--- a/src/core/lib/transport/transport.h
+++ b/src/core/lib/transport/transport.h
@@ -100,6 +100,11 @@
 void grpc_transport_move_stats(grpc_transport_stream_stats *from,
                                grpc_transport_stream_stats *to);
 
+typedef struct {
+  grpc_closure closure;
+  void *args[2];
+} grpc_transport_private_op_data;
+
 /* Transport stream op: a set of operations to perform on a transport
    against a single stream */
 typedef struct grpc_transport_stream_op {
@@ -149,6 +154,12 @@
 
   /* Indexes correspond to grpc_context_index enum values */
   grpc_call_context_element *context;
+
+  /***************************************************************************
+   * remaining fields are initialized and used at the discretion of the
+   * transport implementation */
+
+  grpc_transport_private_op_data transport_private;
 } grpc_transport_stream_op;
 
 /** Transport op: a set of operations to perform on a transport as a whole */
@@ -182,6 +193,12 @@
   grpc_pollset_set *bind_pollset_set;
   /** send a ping, call this back if not NULL */
   grpc_closure *send_ping;
+
+  /***************************************************************************
+   * remaining fields are initialized and used at the discretion of the
+   * transport implementation */
+
+  grpc_transport_private_op_data transport_private;
 } grpc_transport_op;
 
 /* Returns the amount of memory required to store a grpc_stream for this
@@ -273,6 +290,10 @@
 char *grpc_transport_get_peer(grpc_exec_ctx *exec_ctx,
                               grpc_transport *transport);
 
+/* Allocate a grpc_transport_op, and preconfigure the on_consumed closure to
+   \a on_consumed and then delete the returned transport op */
+grpc_transport_op *grpc_make_transport_op(grpc_closure *on_consumed);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/src/csharp/Grpc.Tools.nuspec b/src/csharp/Grpc.Tools.nuspec
index 31d1bed..0c937ab 100644
--- a/src/csharp/Grpc.Tools.nuspec
+++ b/src/csharp/Grpc.Tools.nuspec
@@ -16,17 +16,18 @@
     <tags>gRPC RPC Protocol HTTP/2</tags>
   </metadata>
   <files>
-    <file src="protoc_plugins\windows_x86\protoc.exe" target="tools\windows_x86\protoc.exe" />
-    <file src="protoc_plugins\windows_x86\grpc_csharp_plugin.exe" target="tools\windows_x86\grpc_csharp_plugin.exe" />
-    <file src="protoc_plugins\windows_x64\protoc.exe" target="tools\windows_x64\protoc.exe" />
-    <file src="protoc_plugins\windows_x64\grpc_csharp_plugin.exe" target="tools\windows_x64\grpc_csharp_plugin.exe" />
-    <file src="protoc_plugins\linux_x86\protoc" target="tools\linux_x86\protoc" />
-    <file src="protoc_plugins\linux_x86\grpc_csharp_plugin" target="tools\linux_x86\grpc_csharp_plugin" />
-    <file src="protoc_plugins\linux_x64\protoc" target="tools\linux_x64\protoc" />
-    <file src="protoc_plugins\linux_x64\grpc_csharp_plugin" target="tools\linux_x64\grpc_csharp_plugin" />
-    <file src="protoc_plugins\macosx_x86\protoc" target="tools\macosx_x86\protoc" />
-    <file src="protoc_plugins\macosx_x86\grpc_csharp_plugin" target="tools\macosx_x86\grpc_csharp_plugin" />
-    <file src="protoc_plugins\macosx_x64\protoc" target="tools\macosx_x64\protoc" />
-    <file src="protoc_plugins\macosx_x64\grpc_csharp_plugin" target="tools\macosx_x64\grpc_csharp_plugin" />
+    <!-- forward slashes in src path enable building on Linux -->
+    <file src="protoc_plugins/windows_x86/protoc.exe" target="tools\windows_x86\protoc.exe" />
+    <file src="protoc_plugins/windows_x86/grpc_csharp_plugin.exe" target="tools\windows_x86\grpc_csharp_plugin.exe" />
+    <file src="protoc_plugins/windows_x64/protoc.exe" target="tools\windows_x64\protoc.exe" />
+    <file src="protoc_plugins/windows_x64/grpc_csharp_plugin.exe" target="tools\windows_x64\grpc_csharp_plugin.exe" />
+    <file src="protoc_plugins/linux_x86/protoc" target="tools\linux_x86\protoc" />
+    <file src="protoc_plugins/linux_x86/grpc_csharp_plugin" target="tools\linux_x86\grpc_csharp_plugin" />
+    <file src="protoc_plugins/linux_x64/protoc" target="tools\linux_x64\protoc" />
+    <file src="protoc_plugins/linux_x64/grpc_csharp_plugin" target="tools\linux_x64\grpc_csharp_plugin" />
+    <file src="protoc_plugins/macosx_x86/protoc" target="tools\macosx_x86\protoc" />
+    <file src="protoc_plugins/macosx_x86/grpc_csharp_plugin" target="tools\macosx_x86\grpc_csharp_plugin" />
+    <file src="protoc_plugins/macosx_x64/protoc" target="tools\macosx_x64\protoc" />
+    <file src="protoc_plugins/macosx_x64/grpc_csharp_plugin" target="tools\macosx_x64\grpc_csharp_plugin" />
   </files>
 </package>
diff --git a/src/csharp/build_packages.bat b/src/csharp/build_packages.bat
index b92189c..c0036df 100644
--- a/src/csharp/build_packages.bat
+++ b/src/csharp/build_packages.bat
@@ -29,6 +29,10 @@
 
 @rem Builds gRPC NuGet packages
 
+@rem This way of building nuget packages is now obsolete. C# nuget packages
+@rem with CoreCLR support are now being built using the dotnet cli
+@rem in build_packages_dotnetcli.sh
+
 @rem Current package versions
 set VERSION=1.1.0-dev
 set PROTOBUF_VERSION=3.0.0
@@ -77,8 +81,8 @@
 xcopy /Y /I *.nupkg ..\..\artifacts\
 
 @rem create a zipfile with the artifacts as well
-powershell -Command "Add-Type -Assembly 'System.IO.Compression.FileSystem'; [System.IO.Compression.ZipFile]::CreateFromDirectory('..\..\artifacts', 'csharp_nugets.zip');"
-xcopy /Y /I csharp_nugets.zip ..\..\artifacts\
+powershell -Command "Add-Type -Assembly 'System.IO.Compression.FileSystem'; [System.IO.Compression.ZipFile]::CreateFromDirectory('..\..\artifacts', 'csharp_nugets_obsolete.zip');"
+xcopy /Y /I csharp_nugets_obsolete.zip ..\..\artifacts\
 
 goto :EOF
 
diff --git a/src/csharp/build_packages_dotnetcli.sh b/src/csharp/build_packages_dotnetcli.sh
index 2807278..3c127f3 100755
--- a/src/csharp/build_packages_dotnetcli.sh
+++ b/src/csharp/build_packages_dotnetcli.sh
@@ -34,9 +34,6 @@
 
 mkdir -p ../../artifacts/
 
-# IMPORTANT: NuGet packages generated by dotnet CLI are considered experimental.
-# The official nugets are generated by src/csharp/build_packages.bat
-
 mkdir -p nativelibs/windows_x86 nativelibs/windows_x64 \
     nativelibs/linux_x86 nativelibs/linux_x64 \
     nativelibs/macosx_x86 nativelibs/macosx_x64
diff --git a/src/proto/grpc/lb/v1/load_balancer.options b/src/proto/grpc/lb/v1/load_balancer.options
index d903669..a9398d5 100644
--- a/src/proto/grpc/lb/v1/load_balancer.options
+++ b/src/proto/grpc/lb/v1/load_balancer.options
@@ -1,6 +1,6 @@
 grpc.lb.v1.InitialLoadBalanceRequest.name max_size:128
 grpc.lb.v1.InitialLoadBalanceResponse.client_config max_size:64
 grpc.lb.v1.InitialLoadBalanceResponse.load_balancer_delegate max_size:64
-grpc.lb.v1.Server.ip_address max_size:46
-grpc.lb.v1.Server.load_balance_token max_size:64
+grpc.lb.v1.Server.ip_address max_size:16
+grpc.lb.v1.Server.load_balance_token max_size:65
 load_balancer.proto no_unions:true
diff --git a/src/proto/grpc/lb/v1/load_balancer.proto b/src/proto/grpc/lb/v1/load_balancer.proto
index 1bcad0b..210fba1 100644
--- a/src/proto/grpc/lb/v1/load_balancer.proto
+++ b/src/proto/grpc/lb/v1/load_balancer.proto
@@ -32,7 +32,6 @@
 package grpc.lb.v1;
 
 message Duration {
-
   // Signed seconds of the span of time. Must be from -315,576,000,000
   // to +315,576,000,000 inclusive.
   int64 seconds = 1;
@@ -93,21 +92,16 @@
 }
 
 message InitialLoadBalanceResponse {
-  oneof initial_response_type {
-    // TODO(zhangkun83): ClientConfig not yet defined
-    //ClientConfig client_config = 1;
-
-    // This is an application layer redirect that indicates the client should
-    // use the specified server for load balancing. When this field is set in
-    // the response, the client should open a separate connection to the
-    // load_balancer_delegate and call the BalanceLoad method.
-    string load_balancer_delegate = 2;
-  }
+  // This is an application layer redirect that indicates the client should use
+  // the specified server for load balancing. When this field is non-empty in
+  // the response, the client should open a separate connection to the
+  // load_balancer_delegate and call the BalanceLoad method.
+  string load_balancer_delegate = 1;
 
   // This interval defines how often the client should send the client stats
   // to the load balancer. Stats should only be reported when the duration is
   // positive.
-  Duration client_stats_report_interval = 3;
+  Duration client_stats_report_interval = 2;
 }
 
 message ServerList {
@@ -125,14 +119,17 @@
 }
 
 message Server {
-  // A resolved address and port for the server. The IP address string may
+  // A resolved address for the server, serialized in network-byte-order. It may
   // either be an IPv4 or IPv6 address.
-  string ip_address = 1;
+  bytes ip_address = 1;
+
+  // A resolved port number for the server.
   int32 port = 2;
 
-  // An opaque token that is passed from the client to the server in metadata.
-  // The server may expect this token to indicate that the request from the
-  // client was load balanced.
+  // An opaque but printable token given to the frontend for each pick. All
+  // frontend requests for that pick must include the token in its initial
+  // metadata. The token is used by the backend to verify the request and to
+  // allow the backend to report load to the gRPC LB system.
   string load_balance_token = 3;
 
   // Indicates whether this particular request should be dropped by the client
diff --git a/src/python/grpcio/commands.py b/src/python/grpcio/commands.py
index d36ac23..ea3b6f3 100644
--- a/src/python/grpcio/commands.py
+++ b/src/python/grpcio/commands.py
@@ -53,6 +53,7 @@
 GRPC_STEM = os.path.abspath(PYTHON_STEM + '../../../../')
 PROTO_STEM = os.path.join(GRPC_STEM, 'src', 'proto')
 PROTO_GEN_STEM = os.path.join(GRPC_STEM, 'src', 'python', 'gens')
+CYTHON_STEM = os.path.join(PYTHON_STEM, 'grpc', '_cython')
 
 CONF_PY_ADDENDUM = """
 extensions.append('sphinx.ext.napoleon')
@@ -244,7 +245,7 @@
     extensions,
     include_path=[
       include_dir for extension in extensions for include_dir in extension.include_dirs
-    ],
+    ] + [CYTHON_STEM],
     compiler_directives=cython_compiler_directives
   )
 
diff --git a/src/python/grpcio/grpc/_cython/_cygrpc/security.pyx.pxi b/src/python/grpcio/grpc/_cython/_cygrpc/security.pyx.pxi
index 23cee7b..20fc1c5 100644
--- a/src/python/grpcio/grpc/_cython/_cygrpc/security.pyx.pxi
+++ b/src/python/grpcio/grpc/_cython/_cygrpc/security.pyx.pxi
@@ -35,7 +35,7 @@
 cdef grpc_ssl_roots_override_result ssl_roots_override_callback(
     char **pem_root_certs) with gil:
   temporary_pem_root_certs = pkg_resources.resource_string(
-      'grpc._cython', '_credentials/roots.pem')
+      __name__.rstrip('.cygrpc'), '_credentials/roots.pem')
   pem_root_certs[0] = <char *>gpr_malloc(len(temporary_pem_root_certs) + 1)
   memcpy(
       pem_root_certs[0], <char *>temporary_pem_root_certs,
diff --git a/src/python/grpcio/grpc/_cython/cygrpc.pxd b/src/python/grpcio/grpc/_cython/cygrpc.pxd
index 9779534..2645463 100644
--- a/src/python/grpcio/grpc/_cython/cygrpc.pxd
+++ b/src/python/grpcio/grpc/_cython/cygrpc.pxd
@@ -27,12 +27,12 @@
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-include "grpc/_cython/_cygrpc/grpc.pxi"
+include "_cygrpc/grpc.pxi"
 
-include "grpc/_cython/_cygrpc/call.pxd.pxi"
-include "grpc/_cython/_cygrpc/channel.pxd.pxi"
-include "grpc/_cython/_cygrpc/credentials.pxd.pxi"
-include "grpc/_cython/_cygrpc/completion_queue.pxd.pxi"
-include "grpc/_cython/_cygrpc/records.pxd.pxi"
-include "grpc/_cython/_cygrpc/security.pxd.pxi"
-include "grpc/_cython/_cygrpc/server.pxd.pxi"
+include "_cygrpc/call.pxd.pxi"
+include "_cygrpc/channel.pxd.pxi"
+include "_cygrpc/credentials.pxd.pxi"
+include "_cygrpc/completion_queue.pxd.pxi"
+include "_cygrpc/records.pxd.pxi"
+include "_cygrpc/security.pxd.pxi"
+include "_cygrpc/server.pxd.pxi"
diff --git a/src/python/grpcio/grpc/_cython/cygrpc.pyx b/src/python/grpcio/grpc/_cython/cygrpc.pyx
index 0808999..e1bd046 100644
--- a/src/python/grpcio/grpc/_cython/cygrpc.pyx
+++ b/src/python/grpcio/grpc/_cython/cygrpc.pyx
@@ -35,14 +35,14 @@
 
 # TODO(atash): figure out why the coverage tool gets confused about the Cython
 # coverage plugin when the following files don't have a '.pxi' suffix.
-include "grpc/_cython/_cygrpc/grpc_string.pyx.pxi"
-include "grpc/_cython/_cygrpc/call.pyx.pxi"
-include "grpc/_cython/_cygrpc/channel.pyx.pxi"
-include "grpc/_cython/_cygrpc/credentials.pyx.pxi"
-include "grpc/_cython/_cygrpc/completion_queue.pyx.pxi"
-include "grpc/_cython/_cygrpc/records.pyx.pxi"
-include "grpc/_cython/_cygrpc/security.pyx.pxi"
-include "grpc/_cython/_cygrpc/server.pyx.pxi"
+include "_cygrpc/grpc_string.pyx.pxi"
+include "_cygrpc/call.pyx.pxi"
+include "_cygrpc/channel.pyx.pxi"
+include "_cygrpc/credentials.pyx.pxi"
+include "_cygrpc/completion_queue.pyx.pxi"
+include "_cygrpc/records.pyx.pxi"
+include "_cygrpc/security.pyx.pxi"
+include "_cygrpc/server.pyx.pxi"
 
 #
 # initialize gRPC
diff --git a/src/python/grpcio/grpc_core_dependencies.py b/src/python/grpcio/grpc_core_dependencies.py
index be7f30c..d53f46b 100644
--- a/src/python/grpcio/grpc_core_dependencies.py
+++ b/src/python/grpcio/grpc_core_dependencies.py
@@ -50,6 +50,7 @@
   'src/core/lib/support/log_linux.c',
   'src/core/lib/support/log_posix.c',
   'src/core/lib/support/log_windows.c',
+  'src/core/lib/support/mpscq.c',
   'src/core/lib/support/murmur_hash.c',
   'src/core/lib/support/percent_encoding.c',
   'src/core/lib/support/slice.c',
@@ -92,6 +93,7 @@
   'src/core/lib/http/httpcli.c',
   'src/core/lib/http/parser.c',
   'src/core/lib/iomgr/closure.c',
+  'src/core/lib/iomgr/combiner.c',
   'src/core/lib/iomgr/endpoint.c',
   'src/core/lib/iomgr/endpoint_pair_posix.c',
   'src/core/lib/iomgr/endpoint_pair_windows.c',
diff --git a/templates/src/csharp/build_packages.bat.template b/templates/src/csharp/build_packages.bat.template
index 5cbd8e3..87c4b5a 100644
--- a/templates/src/csharp/build_packages.bat.template
+++ b/templates/src/csharp/build_packages.bat.template
@@ -31,6 +31,10 @@
   
   @rem Builds gRPC NuGet packages
   
+  @rem This way of building nuget packages is now obsolete. C# nuget packages
+  @rem with CoreCLR support are now being built using the dotnet cli
+  @rem in build_packages_dotnetcli.sh
+  
   @rem Current package versions
   set VERSION=${settings.csharp_version}
   set PROTOBUF_VERSION=3.0.0
@@ -79,8 +83,8 @@
   xcopy /Y /I *.nupkg ..\..\artifacts${"\\"}
   
   @rem create a zipfile with the artifacts as well
-  powershell -Command "Add-Type -Assembly 'System.IO.Compression.FileSystem'; [System.IO.Compression.ZipFile]::CreateFromDirectory('..\..\artifacts', 'csharp_nugets.zip');"
-  xcopy /Y /I csharp_nugets.zip ..\..\artifacts${"\\"}
+  powershell -Command "Add-Type -Assembly 'System.IO.Compression.FileSystem'; [System.IO.Compression.ZipFile]::CreateFromDirectory('..\..\artifacts', 'csharp_nugets_obsolete.zip');"
+  xcopy /Y /I csharp_nugets_obsolete.zip ..\..\artifacts${"\\"}
   
   goto :EOF
   
diff --git a/templates/src/csharp/build_packages_dotnetcli.sh.template b/templates/src/csharp/build_packages_dotnetcli.sh.template
index b8e40a0..99b049a 100755
--- a/templates/src/csharp/build_packages_dotnetcli.sh.template
+++ b/templates/src/csharp/build_packages_dotnetcli.sh.template
@@ -36,9 +36,6 @@
   
   mkdir -p ../../artifacts/
   
-  # IMPORTANT: NuGet packages generated by dotnet CLI are considered experimental.
-  # The official nugets are generated by src/csharp/build_packages.bat
-  
   mkdir -p nativelibs/windows_x86 nativelibs/windows_x64 ${"\\"}
       nativelibs/linux_x86 nativelibs/linux_x64 ${"\\"}
       nativelibs/macosx_x86 nativelibs/macosx_x64
diff --git a/test/core/iomgr/combiner_test.c b/test/core/iomgr/combiner_test.c
new file mode 100644
index 0000000..197998c
--- /dev/null
+++ b/test/core/iomgr/combiner_test.c
@@ -0,0 +1,164 @@
+/*
+ *
+ * Copyright 2015, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include "src/core/lib/iomgr/combiner.h"
+
+#include <grpc/grpc.h>
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+#include <grpc/support/thd.h>
+#include <grpc/support/useful.h>
+
+#include "test/core/util/test_config.h"
+
+static void test_no_op(void) {
+  gpr_log(GPR_DEBUG, "test_no_op");
+  grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
+  grpc_combiner_destroy(&exec_ctx, grpc_combiner_create(NULL));
+  grpc_exec_ctx_finish(&exec_ctx);
+}
+
+static void set_bool_to_true(grpc_exec_ctx *exec_ctx, void *value,
+                             grpc_error *error) {
+  *(bool *)value = true;
+}
+
+static void test_execute_one(void) {
+  gpr_log(GPR_DEBUG, "test_execute_one");
+
+  grpc_combiner *lock = grpc_combiner_create(NULL);
+  bool done = false;
+  grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
+  grpc_combiner_execute(&exec_ctx, lock,
+                        grpc_closure_create(set_bool_to_true, &done),
+                        GRPC_ERROR_NONE);
+  grpc_exec_ctx_flush(&exec_ctx);
+  GPR_ASSERT(done);
+  grpc_combiner_destroy(&exec_ctx, lock);
+  grpc_exec_ctx_finish(&exec_ctx);
+}
+
+typedef struct {
+  size_t ctr;
+  grpc_combiner *lock;
+} thd_args;
+
+typedef struct {
+  size_t *ctr;
+  size_t value;
+} ex_args;
+
+static void check_one(grpc_exec_ctx *exec_ctx, void *a, grpc_error *error) {
+  ex_args *args = a;
+  GPR_ASSERT(*args->ctr == args->value - 1);
+  *args->ctr = args->value;
+  gpr_free(a);
+}
+
+static void execute_many_loop(void *a) {
+  thd_args *args = a;
+  grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
+  size_t n = 1;
+  for (size_t i = 0; i < 10; i++) {
+    for (size_t j = 0; j < 10000; j++) {
+      ex_args *c = gpr_malloc(sizeof(*c));
+      c->ctr = &args->ctr;
+      c->value = n++;
+      grpc_combiner_execute(&exec_ctx, args->lock,
+                            grpc_closure_create(check_one, c), GRPC_ERROR_NONE);
+      grpc_exec_ctx_flush(&exec_ctx);
+    }
+    // sleep for a little bit, to test a combiner draining and another thread
+    // picking it up
+    gpr_sleep_until(GRPC_TIMEOUT_MILLIS_TO_DEADLINE(100));
+  }
+  grpc_exec_ctx_finish(&exec_ctx);
+}
+
+static void test_execute_many(void) {
+  gpr_log(GPR_DEBUG, "test_execute_many");
+
+  grpc_combiner *lock = grpc_combiner_create(NULL);
+  gpr_thd_id thds[100];
+  thd_args ta[GPR_ARRAY_SIZE(thds)];
+  for (size_t i = 0; i < GPR_ARRAY_SIZE(thds); i++) {
+    gpr_thd_options options = gpr_thd_options_default();
+    gpr_thd_options_set_joinable(&options);
+    ta[i].ctr = 0;
+    ta[i].lock = lock;
+    GPR_ASSERT(gpr_thd_new(&thds[i], execute_many_loop, &ta[i], &options));
+  }
+  for (size_t i = 0; i < GPR_ARRAY_SIZE(thds); i++) {
+    gpr_thd_join(thds[i]);
+  }
+  grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
+  grpc_combiner_destroy(&exec_ctx, lock);
+  grpc_exec_ctx_finish(&exec_ctx);
+}
+
+static bool got_in_finally = false;
+
+static void in_finally(grpc_exec_ctx *exec_ctx, void *arg, grpc_error *error) {
+  got_in_finally = true;
+}
+
+static void add_finally(grpc_exec_ctx *exec_ctx, void *arg, grpc_error *error) {
+  grpc_combiner_execute_finally(exec_ctx, arg,
+                                grpc_closure_create(in_finally, NULL),
+                                GRPC_ERROR_NONE, false);
+}
+
+static void test_execute_finally(void) {
+  gpr_log(GPR_DEBUG, "test_execute_finally");
+
+  grpc_combiner *lock = grpc_combiner_create(NULL);
+  grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
+  grpc_combiner_execute(&exec_ctx, lock, grpc_closure_create(add_finally, lock),
+                        GRPC_ERROR_NONE);
+  grpc_exec_ctx_flush(&exec_ctx);
+  GPR_ASSERT(got_in_finally);
+  grpc_combiner_destroy(&exec_ctx, lock);
+  grpc_exec_ctx_finish(&exec_ctx);
+}
+
+int main(int argc, char **argv) {
+  grpc_test_init(argc, argv);
+  grpc_init();
+  test_no_op();
+  test_execute_one();
+  test_execute_finally();
+  test_execute_many();
+  grpc_shutdown();
+
+  return 0;
+}
diff --git a/test/core/support/mpscq_test.c b/test/core/support/mpscq_test.c
new file mode 100644
index 0000000..491eb91
--- /dev/null
+++ b/test/core/support/mpscq_test.c
@@ -0,0 +1,206 @@
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include "src/core/lib/support/mpscq.h"
+
+#include <stdlib.h>
+
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+#include <grpc/support/sync.h>
+#include <grpc/support/thd.h>
+#include <grpc/support/useful.h>
+#include "test/core/util/test_config.h"
+
+typedef struct test_node {
+  gpr_mpscq_node node;
+  size_t i;
+  size_t *ctr;
+} test_node;
+
+static test_node *new_node(size_t i, size_t *ctr) {
+  test_node *n = gpr_malloc(sizeof(test_node));
+  n->i = i;
+  n->ctr = ctr;
+  return n;
+}
+
+static void test_serial(void) {
+  gpr_log(GPR_DEBUG, "test_serial");
+  gpr_mpscq q;
+  gpr_mpscq_init(&q);
+  for (size_t i = 0; i < 10000000; i++) {
+    gpr_mpscq_push(&q, &new_node(i, NULL)->node);
+  }
+  for (size_t i = 0; i < 10000000; i++) {
+    test_node *n = (test_node *)gpr_mpscq_pop(&q);
+    GPR_ASSERT(n);
+    GPR_ASSERT(n->i == i);
+    gpr_free(n);
+  }
+}
+
+typedef struct {
+  size_t ctr;
+  gpr_mpscq *q;
+  gpr_event *start;
+} thd_args;
+
+#define THREAD_ITERATIONS 100000
+
+static void test_thread(void *args) {
+  thd_args *a = args;
+  gpr_event_wait(a->start, gpr_inf_future(GPR_CLOCK_REALTIME));
+  for (size_t i = 1; i <= THREAD_ITERATIONS; i++) {
+    gpr_mpscq_push(a->q, &new_node(i, &a->ctr)->node);
+  }
+}
+
+static void test_mt(void) {
+  gpr_log(GPR_DEBUG, "test_mt");
+  gpr_event start;
+  gpr_event_init(&start);
+  gpr_thd_id thds[100];
+  thd_args ta[GPR_ARRAY_SIZE(thds)];
+  gpr_mpscq q;
+  gpr_mpscq_init(&q);
+  for (size_t i = 0; i < GPR_ARRAY_SIZE(thds); i++) {
+    gpr_thd_options options = gpr_thd_options_default();
+    gpr_thd_options_set_joinable(&options);
+    ta[i].ctr = 0;
+    ta[i].q = &q;
+    ta[i].start = &start;
+    GPR_ASSERT(gpr_thd_new(&thds[i], test_thread, &ta[i], &options));
+  }
+  size_t num_done = 0;
+  size_t spins = 0;
+  gpr_event_set(&start, (void *)1);
+  while (num_done != GPR_ARRAY_SIZE(thds)) {
+    gpr_mpscq_node *n;
+    while ((n = gpr_mpscq_pop(&q)) == NULL) {
+      spins++;
+    }
+    test_node *tn = (test_node *)n;
+    GPR_ASSERT(*tn->ctr == tn->i - 1);
+    *tn->ctr = tn->i;
+    if (tn->i == THREAD_ITERATIONS) num_done++;
+    gpr_free(tn);
+  }
+  gpr_log(GPR_DEBUG, "spins: %" PRIdPTR, spins);
+  for (size_t i = 0; i < GPR_ARRAY_SIZE(thds); i++) {
+    gpr_thd_join(thds[i]);
+  }
+  gpr_mpscq_destroy(&q);
+}
+
+typedef struct {
+  thd_args *ta;
+  size_t num_thds;
+  gpr_mu mu;
+  size_t num_done;
+  size_t spins;
+  gpr_mpscq *q;
+  gpr_event *start;
+} pull_args;
+
+static void pull_thread(void *arg) {
+  pull_args *pa = arg;
+  gpr_event_wait(pa->start, gpr_inf_future(GPR_CLOCK_REALTIME));
+
+  for (;;) {
+    gpr_mu_lock(&pa->mu);
+    if (pa->num_done == pa->num_thds) {
+      gpr_mu_unlock(&pa->mu);
+      return;
+    }
+    gpr_mpscq_node *n;
+    while ((n = gpr_mpscq_pop(pa->q)) == NULL) {
+      pa->spins++;
+    }
+    test_node *tn = (test_node *)n;
+    GPR_ASSERT(*tn->ctr == tn->i - 1);
+    *tn->ctr = tn->i;
+    if (tn->i == THREAD_ITERATIONS) pa->num_done++;
+    gpr_free(tn);
+    gpr_mu_unlock(&pa->mu);
+  }
+}
+
+static void test_mt_multipop(void) {
+  gpr_log(GPR_DEBUG, "test_mt_multipop");
+  gpr_event start;
+  gpr_event_init(&start);
+  gpr_thd_id thds[100];
+  gpr_thd_id pull_thds[100];
+  thd_args ta[GPR_ARRAY_SIZE(thds)];
+  gpr_mpscq q;
+  gpr_mpscq_init(&q);
+  for (size_t i = 0; i < GPR_ARRAY_SIZE(thds); i++) {
+    gpr_thd_options options = gpr_thd_options_default();
+    gpr_thd_options_set_joinable(&options);
+    ta[i].ctr = 0;
+    ta[i].q = &q;
+    ta[i].start = &start;
+    GPR_ASSERT(gpr_thd_new(&thds[i], test_thread, &ta[i], &options));
+  }
+  pull_args pa;
+  pa.ta = ta;
+  pa.num_thds = GPR_ARRAY_SIZE(thds);
+  pa.spins = 0;
+  pa.num_done = 0;
+  pa.q = &q;
+  pa.start = &start;
+  gpr_mu_init(&pa.mu);
+  for (size_t i = 0; i < GPR_ARRAY_SIZE(pull_thds); i++) {
+    gpr_thd_options options = gpr_thd_options_default();
+    gpr_thd_options_set_joinable(&options);
+    GPR_ASSERT(gpr_thd_new(&pull_thds[i], pull_thread, &pa, &options));
+  }
+  gpr_event_set(&start, (void *)1);
+  for (size_t i = 0; i < GPR_ARRAY_SIZE(pull_thds); i++) {
+    gpr_thd_join(pull_thds[i]);
+  }
+  gpr_log(GPR_DEBUG, "spins: %" PRIdPTR, pa.spins);
+  for (size_t i = 0; i < GPR_ARRAY_SIZE(thds); i++) {
+    gpr_thd_join(thds[i]);
+  }
+  gpr_mpscq_destroy(&q);
+}
+
+int main(int argc, char **argv) {
+  grpc_test_init(argc, argv);
+  test_serial();
+  test_mt();
+  test_mt_multipop();
+  return 0;
+}
diff --git a/test/core/surface/lame_client_test.c b/test/core/surface/lame_client_test.c
index 2894b0c..6afcefc 100644
--- a/test/core/surface/lame_client_test.c
+++ b/test/core/surface/lame_client_test.c
@@ -49,32 +49,31 @@
 
 void verify_connectivity(grpc_exec_ctx *exec_ctx, void *arg,
                          grpc_error *error) {
-  grpc_transport_op *op = arg;
-  GPR_ASSERT(GRPC_CHANNEL_SHUTDOWN == *op->connectivity_state);
+  grpc_connectivity_state *state = arg;
+  GPR_ASSERT(GRPC_CHANNEL_SHUTDOWN == *state);
   GPR_ASSERT(error == GRPC_ERROR_NONE);
 }
 
 void do_nothing(grpc_exec_ctx *exec_ctx, void *arg, grpc_error *error) {}
 
 void test_transport_op(grpc_channel *channel) {
-  grpc_transport_op op;
+  grpc_transport_op *op;
   grpc_channel_element *elem;
   grpc_connectivity_state state = GRPC_CHANNEL_IDLE;
   grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
 
-  memset(&op, 0, sizeof(op));
-  grpc_closure_init(&transport_op_cb, verify_connectivity, &op);
+  grpc_closure_init(&transport_op_cb, verify_connectivity, &state);
 
-  op.on_connectivity_state_change = &transport_op_cb;
-  op.connectivity_state = &state;
+  op = grpc_make_transport_op(NULL);
+  op->on_connectivity_state_change = &transport_op_cb;
+  op->connectivity_state = &state;
   elem = grpc_channel_stack_element(grpc_channel_get_channel_stack(channel), 0);
-  elem->filter->start_transport_op(&exec_ctx, elem, &op);
+  elem->filter->start_transport_op(&exec_ctx, elem, op);
   grpc_exec_ctx_finish(&exec_ctx);
 
-  memset(&op, 0, sizeof(op));
   grpc_closure_init(&transport_op_cb, do_nothing, NULL);
-  op.on_consumed = &transport_op_cb;
-  elem->filter->start_transport_op(&exec_ctx, elem, &op);
+  op = grpc_make_transport_op(&transport_op_cb);
+  elem->filter->start_transport_op(&exec_ctx, elem, op);
   grpc_exec_ctx_finish(&exec_ctx);
 }
 
diff --git a/test/cpp/end2end/end2end_test.cc b/test/cpp/end2end/end2end_test.cc
index 6661492..b1d3ce9 100644
--- a/test/cpp/end2end/end2end_test.cc
+++ b/test/cpp/end2end/end2end_test.cc
@@ -80,11 +80,14 @@
 
 class TestMetadataCredentialsPlugin : public MetadataCredentialsPlugin {
  public:
-  static const char kMetadataKey[];
+  static const char kGoodMetadataKey[];
+  static const char kBadMetadataKey[];
 
-  TestMetadataCredentialsPlugin(grpc::string_ref metadata_value,
+  TestMetadataCredentialsPlugin(grpc::string_ref metadata_key,
+                                grpc::string_ref metadata_value,
                                 bool is_blocking, bool is_successful)
-      : metadata_value_(metadata_value.data(), metadata_value.length()),
+      : metadata_key_(metadata_key.data(), metadata_key.length()),
+        metadata_value_(metadata_value.data(), metadata_value.length()),
         is_blocking_(is_blocking),
         is_successful_(is_successful) {}
 
@@ -99,7 +102,7 @@
     EXPECT_TRUE(channel_auth_context.IsPeerAuthenticated());
     EXPECT_TRUE(metadata != nullptr);
     if (is_successful_) {
-      metadata->insert(std::make_pair(kMetadataKey, metadata_value_));
+      metadata->insert(std::make_pair(metadata_key_, metadata_value_));
       return Status::OK;
     } else {
       return Status(StatusCode::NOT_FOUND, kTestCredsPluginErrorMsg);
@@ -107,12 +110,16 @@
   }
 
  private:
+  grpc::string metadata_key_;
   grpc::string metadata_value_;
   bool is_blocking_;
   bool is_successful_;
 };
 
-const char TestMetadataCredentialsPlugin::kMetadataKey[] = "TestPluginMetadata";
+const char TestMetadataCredentialsPlugin::kBadMetadataKey[] =
+    "TestPluginMetadata";
+const char TestMetadataCredentialsPlugin::kGoodMetadataKey[] =
+    "test-plugin-metadata";
 
 class TestAuthMetadataProcessor : public AuthMetadataProcessor {
  public:
@@ -123,13 +130,17 @@
   std::shared_ptr<CallCredentials> GetCompatibleClientCreds() {
     return MetadataCredentialsFromPlugin(
         std::unique_ptr<MetadataCredentialsPlugin>(
-            new TestMetadataCredentialsPlugin(kGoodGuy, is_blocking_, true)));
+            new TestMetadataCredentialsPlugin(
+                TestMetadataCredentialsPlugin::kGoodMetadataKey, kGoodGuy,
+                is_blocking_, true)));
   }
 
   std::shared_ptr<CallCredentials> GetIncompatibleClientCreds() {
     return MetadataCredentialsFromPlugin(
         std::unique_ptr<MetadataCredentialsPlugin>(
-            new TestMetadataCredentialsPlugin("Mr Hyde", is_blocking_, true)));
+            new TestMetadataCredentialsPlugin(
+                TestMetadataCredentialsPlugin::kGoodMetadataKey, "Mr Hyde",
+                is_blocking_, true)));
   }
 
   // Interface implementation
@@ -142,7 +153,7 @@
     EXPECT_TRUE(context != nullptr);
     EXPECT_TRUE(response_metadata != nullptr);
     auto auth_md =
-        auth_metadata.find(TestMetadataCredentialsPlugin::kMetadataKey);
+        auth_metadata.find(TestMetadataCredentialsPlugin::kGoodMetadataKey);
     EXPECT_NE(auth_md, auth_metadata.end());
     string_ref auth_md_value = auth_md->second;
     if (auth_md_value == kGoodGuy) {
@@ -1322,6 +1333,40 @@
   EXPECT_TRUE(s.ok());
 }
 
+TEST_P(SecureEnd2endTest, AuthMetadataPluginKeyFailure) {
+  ResetStub();
+  EchoRequest request;
+  EchoResponse response;
+  ClientContext context;
+  context.set_credentials(
+      MetadataCredentialsFromPlugin(std::unique_ptr<MetadataCredentialsPlugin>(
+          new TestMetadataCredentialsPlugin(
+              TestMetadataCredentialsPlugin::kBadMetadataKey,
+              "Does not matter, will fail the key is invalid.", false, true))));
+  request.set_message("Hello");
+
+  Status s = stub_->Echo(&context, request, &response);
+  EXPECT_FALSE(s.ok());
+  EXPECT_EQ(s.error_code(), StatusCode::UNAUTHENTICATED);
+}
+
+TEST_P(SecureEnd2endTest, AuthMetadataPluginValueFailure) {
+  ResetStub();
+  EchoRequest request;
+  EchoResponse response;
+  ClientContext context;
+  context.set_credentials(
+      MetadataCredentialsFromPlugin(std::unique_ptr<MetadataCredentialsPlugin>(
+          new TestMetadataCredentialsPlugin(
+              TestMetadataCredentialsPlugin::kGoodMetadataKey,
+              "With illegal \n value.", false, true))));
+  request.set_message("Hello");
+
+  Status s = stub_->Echo(&context, request, &response);
+  EXPECT_FALSE(s.ok());
+  EXPECT_EQ(s.error_code(), StatusCode::UNAUTHENTICATED);
+}
+
 TEST_P(SecureEnd2endTest, NonBlockingAuthMetadataPluginFailure) {
   ResetStub();
   EchoRequest request;
@@ -1330,6 +1375,7 @@
   context.set_credentials(
       MetadataCredentialsFromPlugin(std::unique_ptr<MetadataCredentialsPlugin>(
           new TestMetadataCredentialsPlugin(
+              TestMetadataCredentialsPlugin::kGoodMetadataKey,
               "Does not matter, will fail anyway (see 3rd param)", false,
               false))));
   request.set_message("Hello");
@@ -1388,6 +1434,7 @@
   context.set_credentials(
       MetadataCredentialsFromPlugin(std::unique_ptr<MetadataCredentialsPlugin>(
           new TestMetadataCredentialsPlugin(
+              TestMetadataCredentialsPlugin::kGoodMetadataKey,
               "Does not matter, will fail anyway (see 3rd param)", true,
               false))));
   request.set_message("Hello");
diff --git a/test/cpp/grpclb/grpclb_api_test.cc b/test/cpp/grpclb/grpclb_api_test.cc
index 33de1ee..e67189c 100644
--- a/test/cpp/grpclb/grpclb_api_test.cc
+++ b/test/cpp/grpclb/grpclb_api_test.cc
@@ -31,10 +31,12 @@
  *
  */
 
+#include <grpc++/impl/codegen/config.h>
 #include <gtest/gtest.h>
-#include <string>
 
 #include "src/core/ext/lb_policy/grpclb/load_balancer_api.h"
+#include "src/core/lib/iomgr/sockaddr.h"
+#include "src/core/lib/iomgr/sockaddr_utils.h"
 #include "src/proto/grpc/lb/v1/load_balancer.pb.h"  // C++ version
 
 namespace grpc {
@@ -45,8 +47,28 @@
 
 class GrpclbTest : public ::testing::Test {};
 
+grpc::string Ip4ToPackedString(const char* ip_str) {
+  struct in_addr ip4;
+  GPR_ASSERT(inet_pton(AF_INET, ip_str, &ip4) == 1);
+  return grpc::string(reinterpret_cast<const char*>(&ip4), sizeof(ip4));
+}
+
+grpc::string PackedStringToIp(const grpc_grpclb_ip_address& pb_ip) {
+  char ip_str[46] = {0};
+  int af = -1;
+  if (pb_ip.size == 4) {
+    af = AF_INET;
+  } else if (pb_ip.size == 16) {
+    af = AF_INET6;
+  } else {
+    abort();
+  }
+  GPR_ASSERT(inet_ntop(af, pb_ip.bytes, ip_str, 46) != NULL);
+  return ip_str;
+}
+
 TEST_F(GrpclbTest, CreateRequest) {
-  const std::string service_name = "AServiceName";
+  const grpc::string service_name = "AServiceName";
   LoadBalanceRequest request;
   grpc_grpclb_request* c_req = grpc_grpclb_request_create(service_name.c_str());
   gpr_slice slice = grpc_grpclb_request_encode(c_req);
@@ -65,7 +87,7 @@
       initial_response->mutable_client_stats_report_interval();
   client_stats_report_interval->set_seconds(123);
   client_stats_report_interval->set_nanos(456);
-  const std::string encoded_response = response.SerializeAsString();
+  const grpc::string encoded_response = response.SerializeAsString();
   gpr_slice encoded_slice =
       gpr_slice_from_copied_string(encoded_response.c_str());
 
@@ -82,29 +104,31 @@
   LoadBalanceResponse response;
   auto* serverlist = response.mutable_server_list();
   auto* server = serverlist->add_servers();
-  server->set_ip_address("127.0.0.1");
+  server->set_ip_address(Ip4ToPackedString("127.0.0.1"));
   server->set_port(12345);
   server->set_drop_request(true);
   server = response.mutable_server_list()->add_servers();
-  server->set_ip_address("10.0.0.1");
+  server->set_ip_address(Ip4ToPackedString("10.0.0.1"));
   server->set_port(54321);
   server->set_drop_request(false);
   auto* expiration_interval = serverlist->mutable_expiration_interval();
   expiration_interval->set_seconds(888);
   expiration_interval->set_nanos(999);
 
-  const std::string encoded_response = response.SerializeAsString();
-  gpr_slice encoded_slice =
-      gpr_slice_from_copied_string(encoded_response.c_str());
+  const grpc::string encoded_response = response.SerializeAsString();
+  const gpr_slice encoded_slice = gpr_slice_from_copied_buffer(
+      encoded_response.data(), encoded_response.size());
   grpc_grpclb_serverlist* c_serverlist =
       grpc_grpclb_response_parse_serverlist(encoded_slice);
   ASSERT_EQ(c_serverlist->num_servers, 2ul);
   EXPECT_TRUE(c_serverlist->servers[0]->has_ip_address);
-  EXPECT_TRUE(strcmp(c_serverlist->servers[0]->ip_address, "127.0.0.1") == 0);
+  EXPECT_EQ(PackedStringToIp(c_serverlist->servers[0]->ip_address),
+            "127.0.0.1");
   EXPECT_EQ(c_serverlist->servers[0]->port, 12345);
   EXPECT_TRUE(c_serverlist->servers[0]->drop_request);
   EXPECT_TRUE(c_serverlist->servers[1]->has_ip_address);
-  EXPECT_TRUE(strcmp(c_serverlist->servers[1]->ip_address, "10.0.0.1") == 0);
+
+  EXPECT_EQ(PackedStringToIp(c_serverlist->servers[1]->ip_address), "10.0.0.1");
   EXPECT_EQ(c_serverlist->servers[1]->port, 54321);
   EXPECT_FALSE(c_serverlist->servers[1]->drop_request);
 
diff --git a/test/cpp/grpclb/grpclb_test.cc b/test/cpp/grpclb/grpclb_test.cc
index 6f6fb83..95abe38 100644
--- a/test/cpp/grpclb/grpclb_test.cc
+++ b/test/cpp/grpclb/grpclb_test.cc
@@ -37,7 +37,10 @@
 #include <cstring>
 #include <string>
 
+#include <gtest/gtest.h>
+
 #include <grpc/grpc.h>
+#include <grpc/impl/codegen/byte_buffer_reader.h>
 #include <grpc/support/alloc.h>
 #include <grpc/support/host_port.h>
 #include <grpc/support/log.h>
@@ -46,9 +49,11 @@
 #include <grpc/support/thd.h>
 #include <grpc/support/time.h>
 
+#include <grpc++/impl/codegen/config.h>
 extern "C" {
 #include "src/core/ext/client_config/client_channel.h"
 #include "src/core/lib/channel/channel_stack.h"
+#include "src/core/lib/iomgr/sockaddr.h"
 #include "src/core/lib/support/string.h"
 #include "src/core/lib/support/tmpfile.h"
 #include "src/core/lib/surface/channel.h"
@@ -61,16 +66,19 @@
 #include "src/proto/grpc/lb/v1/load_balancer.pb.h"
 
 #define NUM_BACKENDS 4
+#define PAYLOAD "hello you"
 
 // TODO(dgq): Other scenarios in need of testing:
 // - Send an empty serverlist update and verify that the client request blocks
 //   until a new serverlist with actual contents is available.
 // - Send identical serverlist update
+// - Send a serverlist with faulty ip:port addresses (port > 2^16, etc).
 // - Test reception of invalid serverlist
 // - Test pinging
 // - Test against a non-LB server. That server should return UNIMPLEMENTED and
 //   the call should fail.
 // - Random LB server closing the stream unexpectedly.
+// - Test using DNS-resolvable names (localhost?)
 
 namespace grpc {
 namespace {
@@ -105,8 +113,8 @@
     int64_t expiration_interval_secs, int32_t expiration_interval_nanos) {
   // server_list {
   //   servers {
-  //     ip_address: "127.0.0.1"
-  //     port: ...
+  //     ip_address: <in_addr/6 bytes of an IP>
+  //     port: <16 bit uint>
   //     load_balance_token: "token..."
   //   }
   //   ...
@@ -125,21 +133,21 @@
   }
   for (size_t i = 0; i < nports; i++) {
     auto *server = serverlist->add_servers();
-    server->set_ip_address(host);
+    // TODO(dgq): test ipv6
+    struct in_addr ip4;
+    GPR_ASSERT(inet_pton(AF_INET, host, &ip4) == 1);
+    server->set_ip_address(
+        grpc::string(reinterpret_cast<const char *>(&ip4), sizeof(ip4)));
     server->set_port(ports[i]);
     // The following long long int cast is meant to work around the
     // disfunctional implementation of std::to_string in gcc 4.4, which doesn't
     // have a version for int but does have one for long long int.
-    server->set_load_balance_token("token" +
-                                   std::to_string((long long int)ports[i]));
+    string token_data = "token" + std::to_string((long long int)ports[i]);
+    token_data.resize(64, '-');
+    server->set_load_balance_token(token_data);
   }
-
-  gpr_log(GPR_INFO, "generating response: %s",
-          response.ShortDebugString().c_str());
-
-  const gpr_slice response_slice =
-      gpr_slice_from_copied_string(response.SerializeAsString().c_str());
-  return response_slice;
+  const grpc::string &enc_resp = response.SerializeAsString();
+  return gpr_slice_from_copied_buffer(enc_resp.data(), enc_resp.size());
 }
 
 static void drain_cq(grpc_completion_queue *cq) {
@@ -181,6 +189,37 @@
   cq_verify(cqv);
   gpr_log(GPR_INFO, "LB Server[%s] after tag 200", sf->servers_hostport);
 
+  // make sure we've received the initial metadata from the grpclb request.
+  GPR_ASSERT(request_metadata_recv.count > 0);
+  GPR_ASSERT(request_metadata_recv.metadata != NULL);
+
+  // receive request for backends
+  op = ops;
+  op->op = GRPC_OP_RECV_MESSAGE;
+  op->data.recv_message = &request_payload_recv;
+  op->flags = 0;
+  op->reserved = NULL;
+  op++;
+  error = grpc_call_start_batch(s, ops, (size_t)(op - ops), tag(202), NULL);
+  GPR_ASSERT(GRPC_CALL_OK == error);
+  CQ_EXPECT_COMPLETION(cqv, tag(202), 1);
+  cq_verify(cqv);
+  gpr_log(GPR_INFO, "LB Server[%s] after RECV_MSG", sf->servers_hostport);
+
+  // validate initial request.
+  grpc_byte_buffer_reader bbr;
+  grpc_byte_buffer_reader_init(&bbr, request_payload_recv);
+  gpr_slice request_payload_slice = grpc_byte_buffer_reader_readall(&bbr);
+  grpc::lb::v1::LoadBalanceRequest request;
+  request.ParseFromArray(GPR_SLICE_START_PTR(request_payload_slice),
+                         GPR_SLICE_LENGTH(request_payload_slice));
+  GPR_ASSERT(request.has_initial_request());
+  GPR_ASSERT(request.initial_request().name() == "load.balanced.service.name");
+  gpr_slice_unref(request_payload_slice);
+  grpc_byte_buffer_reader_destroy(&bbr);
+  grpc_byte_buffer_destroy(request_payload_recv);
+
+  gpr_slice response_payload_slice;
   op = ops;
   op->op = GRPC_OP_SEND_INITIAL_METADATA;
   op->data.send_initial_metadata.count = 0;
@@ -196,21 +235,6 @@
   GPR_ASSERT(GRPC_CALL_OK == error);
   gpr_log(GPR_INFO, "LB Server[%s] after tag 201", sf->servers_hostport);
 
-  // receive request for backends
-  op = ops;
-  op->op = GRPC_OP_RECV_MESSAGE;
-  op->data.recv_message = &request_payload_recv;
-  op->flags = 0;
-  op->reserved = NULL;
-  op++;
-  error = grpc_call_start_batch(s, ops, (size_t)(op - ops), tag(202), NULL);
-  GPR_ASSERT(GRPC_CALL_OK == error);
-  CQ_EXPECT_COMPLETION(cqv, tag(202), 1);
-  cq_verify(cqv);
-  gpr_log(GPR_INFO, "LB Server[%s] after RECV_MSG", sf->servers_hostport);
-  // TODO(dgq): validate request.
-  grpc_byte_buffer_destroy(request_payload_recv);
-  gpr_slice response_payload_slice;
   for (int i = 0; i < 2; i++) {
     if (i == 0) {
       // First half of the ports.
@@ -303,6 +327,16 @@
       return;
     }
     GPR_ASSERT(ev.type == GRPC_OP_COMPLETE);
+
+    // The following long long int cast is meant to work around the
+    // disfunctional implementation of std::to_string in gcc 4.4, which doesn't
+    // have a version for int but does have one for long long int.
+    string expected_token = "token" + std::to_string((long long int)sf->port);
+    expected_token.resize(64, '-');
+    GPR_ASSERT(contains_metadata(&request_metadata_recv,
+                                 "load-reporting-initial",
+                                 expected_token.c_str()));
+
     gpr_log(GPR_INFO, "Server[%s] after tag 100", sf->servers_hostport);
 
     op = ops;
@@ -321,8 +355,7 @@
     gpr_log(GPR_INFO, "Server[%s] after tag 101", sf->servers_hostport);
 
     bool exit = false;
-    gpr_slice response_payload_slice =
-        gpr_slice_from_copied_string("hello you");
+    gpr_slice response_payload_slice = gpr_slice_from_copied_string(PAYLOAD);
     while (!exit) {
       op = ops;
       op->op = GRPC_OP_RECV_MESSAGE;
@@ -474,10 +507,9 @@
     error = grpc_call_start_batch(c, ops, (size_t)(op - ops), tag(2), NULL);
     GPR_ASSERT(GRPC_CALL_OK == error);
 
-    peer = grpc_call_get_peer(c);
     CQ_EXPECT_COMPLETION(cqv, tag(2), 1);
     cq_verify(cqv);
-    gpr_free(peer);
+    GPR_ASSERT(byte_buffer_eq_string(response_payload_recv, PAYLOAD));
 
     grpc_byte_buffer_destroy(request_payload);
     grpc_byte_buffer_destroy(response_payload_recv);
@@ -583,27 +615,30 @@
                   tf->lb_server_update_delay_ms);
 }
 
-static void setup_test_fixture(test_fixture *tf,
-                               int lb_server_update_delay_ms) {
-  tf->lb_server_update_delay_ms = lb_server_update_delay_ms;
+static test_fixture setup_test_fixture(int lb_server_update_delay_ms) {
+  test_fixture tf;
+  memset(&tf, 0, sizeof(tf));
+  tf.lb_server_update_delay_ms = lb_server_update_delay_ms;
 
   gpr_thd_options options = gpr_thd_options_default();
   gpr_thd_options_set_joinable(&options);
 
   for (int i = 0; i < NUM_BACKENDS; ++i) {
-    setup_server("127.0.0.1", &tf->lb_backends[i]);
-    gpr_thd_new(&tf->lb_backends[i].tid, fork_backend_server,
-                &tf->lb_backends[i], &options);
+    setup_server("127.0.0.1", &tf.lb_backends[i]);
+    gpr_thd_new(&tf.lb_backends[i].tid, fork_backend_server, &tf.lb_backends[i],
+                &options);
   }
 
-  setup_server("127.0.0.1", &tf->lb_server);
-  gpr_thd_new(&tf->lb_server.tid, fork_lb_server, &tf->lb_server, &options);
+  setup_server("127.0.0.1", &tf.lb_server);
+  gpr_thd_new(&tf.lb_server.tid, fork_lb_server, &tf.lb_server, &options);
 
   char *server_uri;
   gpr_asprintf(&server_uri, "ipv4:%s?lb_policy=grpclb&lb_enabled=1",
-               tf->lb_server.servers_hostport);
-  setup_client(server_uri, &tf->client);
+               tf.lb_server.servers_hostport);
+  setup_client(server_uri, &tf.client);
   gpr_free(server_uri);
+
+  return tf;
 }
 
 static void teardown_test_fixture(test_fixture *tf) {
@@ -614,19 +649,13 @@
   teardown_server(&tf->lb_server);
 }
 
-// The LB server will send two updates: batch 1 and batch 2. Each batch
-// contains
-// two addresses, both of a valid and running backend server. Batch 1 is
-// readily
-// available and provided as soon as the client establishes the streaming
-// call.
-// Batch 2 is sent after a delay of \a lb_server_update_delay_ms
-// milliseconds.
+// The LB server will send two updates: batch 1 and batch 2. Each batch contains
+// two addresses, both of a valid and running backend server. Batch 1 is readily
+// available and provided as soon as the client establishes the streaming call.
+// Batch 2 is sent after a delay of \a lb_server_update_delay_ms milliseconds.
 static test_fixture test_update(int lb_server_update_delay_ms) {
   gpr_log(GPR_INFO, "start %s(%d)", __func__, lb_server_update_delay_ms);
-  test_fixture tf;
-  memset(&tf, 0, sizeof(tf));
-  setup_test_fixture(&tf, lb_server_update_delay_ms);
+  test_fixture tf = setup_test_fixture(lb_server_update_delay_ms);
   perform_request(
       &tf.client);  // "consumes" 1st backend server of 1st serverlist
   perform_request(
@@ -642,13 +671,7 @@
   return tf;
 }
 
-}  // namespace
-}  // namespace grpc
-
-int main(int argc, char **argv) {
-  grpc_test_init(argc, argv);
-  grpc_init();
-
+TEST(GrpclbTest, Updates) {
   grpc::test_fixture tf_result;
   // Clients take a bit over one second to complete a call (the last part of the
   // call sleeps for 1 second while verifying the client's completion queue is
@@ -683,7 +706,18 @@
   GPR_ASSERT(tf_result.lb_backends[1].num_calls_serviced > 0);
   GPR_ASSERT(tf_result.lb_backends[2].num_calls_serviced > 0);
   GPR_ASSERT(tf_result.lb_backends[3].num_calls_serviced == 0);
+}
 
+TEST(GrpclbTest, InvalidAddressInServerlist) {}
+
+}  // namespace
+}  // namespace grpc
+
+int main(int argc, char **argv) {
+  ::testing::InitGoogleTest(&argc, argv);
+  grpc_test_init(argc, argv);
+  grpc_init();
+  const auto result = RUN_ALL_TESTS();
   grpc_shutdown();
-  return 0;
+  return result;
 }
diff --git a/test/cpp/qps/client.h b/test/cpp/qps/client.h
index fada4ba..c8809cb 100644
--- a/test/cpp/qps/client.h
+++ b/test/cpp/qps/client.h
@@ -129,13 +129,17 @@
 
 class Client {
  public:
-  Client() : timer_(new UsageTimer), interarrival_timer_() {}
+  Client() : timer_(new UsageTimer), interarrival_timer_() {
+    gpr_event_init(&start_requests_);
+  }
   virtual ~Client() {}
 
   ClientStats Mark(bool reset) {
     Histogram latencies;
     UsageTimer::Result timer_result;
 
+    MaybeStartRequests();
+
     // avoid std::vector for old compilers that expect a copy constructor
     if (reset) {
       Histogram* to_merge = new Histogram[threads_.size()];
@@ -189,7 +193,10 @@
     }
   }
 
-  void EndThreads() { threads_.clear(); }
+  void EndThreads() {
+    MaybeStartRequests();
+    threads_.clear();
+  }
 
   virtual void DestroyMultithreading() = 0;
   virtual bool ThreadFunc(HistogramEntry* histogram, size_t thread_idx) = 0;
@@ -265,6 +272,13 @@
     Thread& operator=(const Thread&);
 
     void ThreadFunc() {
+      while (!gpr_event_wait(
+          &client_->start_requests_,
+          gpr_time_add(gpr_now(GPR_CLOCK_REALTIME),
+                       gpr_time_from_seconds(1, GPR_TIMESPAN)))) {
+        gpr_log(GPR_INFO, "Waiting for benchmark to start");
+      }
+
       for (;;) {
         // run the loop body
         HistogramEntry entry;
@@ -302,6 +316,16 @@
   size_t threads_remaining_;
   std::condition_variable threads_complete_;
 
+  gpr_event start_requests_;
+  bool started_requests_;
+
+  void MaybeStartRequests() {
+    if (!started_requests_) {
+      started_requests_ = true;
+      gpr_event_set(&start_requests_, (void*)1);
+    }
+  }
+
   void CompleteThread() {
     std::lock_guard<std::mutex> g(thread_completion_mu_);
     threads_remaining_--;
@@ -359,7 +383,7 @@
       gpr_log(GPR_INFO, "Connecting to %s", target.c_str());
       GPR_ASSERT(channel_->WaitForConnected(
           gpr_time_add(gpr_now(GPR_CLOCK_REALTIME),
-                       gpr_time_from_seconds(30, GPR_TIMESPAN))));
+                       gpr_time_from_seconds(300, GPR_TIMESPAN))));
       stub_ = create_stub(channel_);
     }
     Channel* get_channel() { return channel_.get(); }
diff --git a/test/cpp/qps/driver.cc b/test/cpp/qps/driver.cc
index f67f353..b4c18bc 100644
--- a/test/cpp/qps/driver.cc
+++ b/test/cpp/qps/driver.cc
@@ -366,12 +366,37 @@
     if (!clients[i].stream->Write(args)) {
       gpr_log(GPR_ERROR, "Could not write args to client %zu", i);
     }
+  }
+
+  for (size_t i = 0; i < num_clients; i++) {
     ClientStatus init_status;
     if (!clients[i].stream->Read(&init_status)) {
       gpr_log(GPR_ERROR, "Client %zu did not yield initial status", i);
     }
   }
 
+  // Send an initial mark: clients can use this to know that everything is ready
+  // to start
+  gpr_log(GPR_INFO, "Initiating");
+  ServerArgs server_mark;
+  server_mark.mutable_mark()->set_reset(true);
+  ClientArgs client_mark;
+  client_mark.mutable_mark()->set_reset(true);
+  ServerStatus server_status;
+  ClientStatus client_status;
+  for (size_t i = 0; i < num_clients; i++) {
+    auto client = &clients[i];
+    if (!client->stream->Write(client_mark)) {
+      gpr_log(GPR_ERROR, "Couldn't write mark to client %zu", i);
+    }
+  }
+  for (size_t i = 0; i < num_clients; i++) {
+    auto client = &clients[i];
+    if (!client->stream->Read(&client_status)) {
+      gpr_log(GPR_ERROR, "Couldn't get status from client %zu", i);
+    }
+  }
+
   // Let everything warmup
   gpr_log(GPR_INFO, "Warming up");
   gpr_timespec start = gpr_now(GPR_CLOCK_REALTIME);
@@ -380,10 +405,6 @@
 
   // Start a run
   gpr_log(GPR_INFO, "Starting");
-  ServerArgs server_mark;
-  server_mark.mutable_mark()->set_reset(true);
-  ClientArgs client_mark;
-  client_mark.mutable_mark()->set_reset(true);
   for (size_t i = 0; i < num_servers; i++) {
     auto server = &servers[i];
     if (!server->stream->Write(server_mark)) {
@@ -396,8 +417,6 @@
       gpr_log(GPR_ERROR, "Couldn't write mark to client %zu", i);
     }
   }
-  ServerStatus server_status;
-  ClientStatus client_status;
   for (size_t i = 0; i < num_servers; i++) {
     auto server = &servers[i];
     if (!server->stream->Read(&server_status)) {
diff --git a/test/cpp/util/proto_reflection_descriptor_database.h b/test/cpp/util/proto_reflection_descriptor_database.h
index eb7cf49..0e69696 100644
--- a/test/cpp/util/proto_reflection_descriptor_database.h
+++ b/test/cpp/util/proto_reflection_descriptor_database.h
@@ -45,6 +45,8 @@
 #include <grpc++/ext/reflection.grpc.pb.h>
 #endif  // GRPC_NO_GENERATED_CODE
 #include <grpc++/grpc++.h>
+#include <grpc++/impl/codegen/config_protobuf.h>
+
 namespace grpc {
 
 // ProtoReflectionDescriptorDatabase takes a stub of ServerReflection and
diff --git a/test/distrib/csharp/run_distrib_test.bat b/test/distrib/csharp/run_distrib_test.bat
index 67bfc58..6cf3811 100644
--- a/test/distrib/csharp/run_distrib_test.bat
+++ b/test/distrib/csharp/run_distrib_test.bat
@@ -31,12 +31,22 @@
 cd /d %~dp0
 
 @rem extract input artifacts
-powershell -Command "Add-Type -Assembly 'System.IO.Compression.FileSystem'; [System.IO.Compression.ZipFile]::ExtractToDirectory('../../../input_artifacts/csharp_nugets.zip', 'TestNugetFeed');"
+powershell -Command "Add-Type -Assembly 'System.IO.Compression.FileSystem'; [System.IO.Compression.ZipFile]::ExtractToDirectory('../../../input_artifacts/csharp_nugets_dotnetcli.zip', 'TestNugetFeed');"
 
 update_version.sh auto
 
 set NUGET=C:\nuget\nuget.exe
-%NUGET% restore || goto :error
+
+@rem TODO(jtattermusch): Get rid of this hack. See #8034
+@rem We can't do just "nuget restore" because restoring a .sln solution doesn't work
+@rem with nuget 3.X. On the other hand, we need nuget 2.12+ to be able to restore
+@rem some of the packages (e.g. System.Interactive.Async), but nuget 2.12
+@rem hasn't been officially released.
+@rem Please note that "Restore nuget packages" in VS2013 and VS2015 GUI works as usual.
+
+cd DistribTest || goto :error
+%NUGET% restore -PackagesDirectory ../packages || goto :error
+cd ..
 
 @call build_vs2015.bat DistribTest.sln %MSBUILD_EXTRA_ARGS% || goto :error
 
diff --git a/test/distrib/csharp/run_distrib_test.sh b/test/distrib/csharp/run_distrib_test.sh
index 64e98d8..0a77c1a 100755
--- a/test/distrib/csharp/run_distrib_test.sh
+++ b/test/distrib/csharp/run_distrib_test.sh
@@ -32,7 +32,7 @@
 
 cd $(dirname $0)
 
-unzip -o "$EXTERNAL_GIT_ROOT/input_artifacts/csharp_nugets.zip" -d TestNugetFeed
+unzip -o "$EXTERNAL_GIT_ROOT/input_artifacts/csharp_nugets_dotnetcli.zip" -d TestNugetFeed
 
 ./update_version.sh auto
 
diff --git a/test/distrib/csharp/run_distrib_test_dotnetcli.sh b/test/distrib/csharp/run_distrib_test_dotnetcli.sh
index f7080be..493c504 100755
--- a/test/distrib/csharp/run_distrib_test_dotnetcli.sh
+++ b/test/distrib/csharp/run_distrib_test_dotnetcli.sh
@@ -32,7 +32,7 @@
 
 cd $(dirname $0)
 
-unzip -o "$EXTERNAL_GIT_ROOT/input_artifacts/csharp_nugets.zip" -d TestNugetFeed
+unzip -o "$EXTERNAL_GIT_ROOT/input_artifacts/csharp_nugets_dotnetcli.zip" -d TestNugetFeed
 
 ./update_version.sh auto
 
diff --git a/third_party/nanopb b/third_party/nanopb
index f8ac463..68a86e9 160000
--- a/third_party/nanopb
+++ b/third_party/nanopb
@@ -1 +1 @@
-Subproject commit f8ac463766281625ad710900479130c7fcb4d63b
+Subproject commit 68a86e96481e6bea987df8de47027847b30c325b
diff --git a/tools/codegen/core/gen_nano_proto.sh b/tools/codegen/core/gen_nano_proto.sh
index c880fc2..df107c2 100755
--- a/tools/codegen/core/gen_nano_proto.sh
+++ b/tools/codegen/core/gen_nano_proto.sh
@@ -123,7 +123,7 @@
 
 # this should be the same version as the submodule we compile against
 # ideally we'd update this as a template to ensure that
-pip install protobuf==3.0.0b2
+pip install protobuf==3.0.0
 
 pushd "$(dirname $INPUT_PROTO)" > /dev/null
 
diff --git a/tools/doxygen/Doxyfile.c++ b/tools/doxygen/Doxyfile.c++
index 59a6e1c..2a56d40 100644
--- a/tools/doxygen/Doxyfile.c++
+++ b/tools/doxygen/Doxyfile.c++
@@ -854,6 +854,7 @@
 include/grpc++/impl/codegen/service_type.h \
 include/grpc++/impl/codegen/status.h \
 include/grpc++/impl/codegen/status_code_enum.h \
+include/grpc++/impl/codegen/status_helper.h \
 include/grpc++/impl/codegen/string_ref.h \
 include/grpc++/impl/codegen/stub_options.h \
 include/grpc++/impl/codegen/sync.h \
diff --git a/tools/doxygen/Doxyfile.c++.internal b/tools/doxygen/Doxyfile.c++.internal
index d94aa42..8739254 100644
--- a/tools/doxygen/Doxyfile.c++.internal
+++ b/tools/doxygen/Doxyfile.c++.internal
@@ -854,6 +854,7 @@
 include/grpc++/impl/codegen/service_type.h \
 include/grpc++/impl/codegen/status.h \
 include/grpc++/impl/codegen/status_code_enum.h \
+include/grpc++/impl/codegen/status_helper.h \
 include/grpc++/impl/codegen/string_ref.h \
 include/grpc++/impl/codegen/stub_options.h \
 include/grpc++/impl/codegen/sync.h \
@@ -885,6 +886,7 @@
 src/core/lib/http/httpcli.h \
 src/core/lib/http/parser.h \
 src/core/lib/iomgr/closure.h \
+src/core/lib/iomgr/combiner.h \
 src/core/lib/iomgr/endpoint.h \
 src/core/lib/iomgr/endpoint_pair.h \
 src/core/lib/iomgr/error.h \
@@ -997,6 +999,7 @@
 src/core/lib/http/httpcli.c \
 src/core/lib/http/parser.c \
 src/core/lib/iomgr/closure.c \
+src/core/lib/iomgr/combiner.c \
 src/core/lib/iomgr/endpoint.c \
 src/core/lib/iomgr/endpoint_pair_posix.c \
 src/core/lib/iomgr/endpoint_pair_windows.c \
diff --git a/tools/doxygen/Doxyfile.core.internal b/tools/doxygen/Doxyfile.core.internal
index e2d44e8..7ffd07b 100644
--- a/tools/doxygen/Doxyfile.core.internal
+++ b/tools/doxygen/Doxyfile.core.internal
@@ -802,6 +802,7 @@
 src/core/lib/http/httpcli.h \
 src/core/lib/http/parser.h \
 src/core/lib/iomgr/closure.h \
+src/core/lib/iomgr/combiner.h \
 src/core/lib/iomgr/endpoint.h \
 src/core/lib/iomgr/endpoint_pair.h \
 src/core/lib/iomgr/error.h \
@@ -961,6 +962,7 @@
 src/core/lib/http/httpcli.c \
 src/core/lib/http/parser.c \
 src/core/lib/iomgr/closure.c \
+src/core/lib/iomgr/combiner.c \
 src/core/lib/iomgr/endpoint.c \
 src/core/lib/iomgr/endpoint_pair_posix.c \
 src/core/lib/iomgr/endpoint_pair_windows.c \
@@ -1178,6 +1180,7 @@
 src/core/lib/support/backoff.h \
 src/core/lib/support/block_annotate.h \
 src/core/lib/support/env.h \
+src/core/lib/support/mpscq.h \
 src/core/lib/support/murmur_hash.h \
 src/core/lib/support/percent_encoding.h \
 src/core/lib/support/stack_lockfree.h \
@@ -1206,6 +1209,7 @@
 src/core/lib/support/log_linux.c \
 src/core/lib/support/log_posix.c \
 src/core/lib/support/log_windows.c \
+src/core/lib/support/mpscq.c \
 src/core/lib/support/murmur_hash.c \
 src/core/lib/support/percent_encoding.c \
 src/core/lib/support/slice.c \
diff --git a/tools/run_tests/build_artifact_protoc.bat b/tools/run_tests/build_artifact_protoc.bat
index e1dc032..3246a90 100644
--- a/tools/run_tests/build_artifact_protoc.bat
+++ b/tools/run_tests/build_artifact_protoc.bat
@@ -32,12 +32,8 @@
 setlocal
 cd third_party/protobuf
 
-powershell -Command "Invoke-WebRequest https://googlemock.googlecode.com/files/gmock-1.7.0.zip -OutFile gmock.zip"
-powershell -Command "Add-Type -Assembly 'System.IO.Compression.FileSystem'; [System.IO.Compression.ZipFile]::ExtractToDirectory('gmock.zip', '.');"
-rename gmock-1.7.0 gmock
-
 cd cmake
-cmake -G "%generator%" || goto :error
+cmake -G "%generator%" -Dprotobuf_BUILD_TESTS=OFF || goto :error
 endlocal
 
 call vsprojects/build_plugins.bat || goto :error
diff --git a/tools/run_tests/performance/scenario_config.py b/tools/run_tests/performance/scenario_config.py
index 99b5596..f4ccfea 100644
--- a/tools/run_tests/performance/scenario_config.py
+++ b/tools/run_tests/performance/scenario_config.py
@@ -38,6 +38,7 @@
 SMOKETEST='smoketest'
 SCALABLE='scalable'
 SWEEP='sweep'
+DEFAULT_CATEGORIES=[SCALABLE, SMOKETEST]
 
 SECURE_SECARGS = {'use_test_ca': True,
                   'server_host_override': 'foo.test.google.fr'}
@@ -94,6 +95,13 @@
   return scenario
 
 
+def geometric_progression(start, stop, step):
+  n = start
+  while n < stop:
+    yield int(round(n))
+    n *= step
+
+
 def _ping_pong_scenario(name, rpc_type,
                         client_type, server_type,
                         secure=True,
@@ -104,8 +112,9 @@
                         server_core_limit=0,
                         async_server_threads=0,
                         warmup_seconds=WARMUP_SECONDS,
-                        categories=[],
-                        channels=None):
+                        categories=DEFAULT_CATEGORIES,
+                        channels=None,
+                        outstanding=None):
   """Creates a basic ping pong scenario."""
   scenario = {
     'name': name,
@@ -142,8 +151,9 @@
     scenario['client_config']['payload_config'] = EMPTY_PROTO_PAYLOAD
 
   if unconstrained_client:
+    outstanding_calls = outstanding if outstanding is not None else OUTSTANDING_REQUESTS[unconstrained_client]
     wide = channels if channels is not None else WIDE
-    deep = int(math.ceil(1.0 * OUTSTANDING_REQUESTS[unconstrained_client] / wide))
+    deep = int(math.ceil(1.0 * outstanding_calls / wide))
 
     scenario['num_clients'] = 0  # use as many client as available.
     scenario['client_config']['outstanding_rpcs_per_channel'] = deep
@@ -245,13 +255,17 @@
             secure=secure,
             categories=[SCALABLE])
 
-        for channels in [1, 3, 10, 31, 100, 316, 1000]:
-          yield _ping_pong_scenario(
-              'cpp_protobuf_%s_unary_qps_unconstrained_%s_%d_channels' % (synchronicity, secstr, channels),
-              rpc_type='UNARY',
-              client_type='ASYNC_CLIENT', server_type='ASYNC_SERVER',
-              unconstrained_client=synchronicity, secure=secure,
-              categories=[SWEEP], channels=channels)
+        for channels in geometric_progression(1, 500, math.sqrt(10)):
+          for outstanding in geometric_progression(1, 20000, math.sqrt(10)):
+              if synchronicity == 'sync' and outstanding > 1200: continue
+              if outstanding < channels: continue
+              yield _ping_pong_scenario(
+                  'cpp_protobuf_%s_unary_qps_unconstrained_%s_%d_channels_%d_outstanding' % (synchronicity, secstr, channels, outstanding),
+                  rpc_type='UNARY',
+                  client_type='%s_CLIENT' % synchronicity.upper(),
+                  server_type='%s_SERVER' % synchronicity.upper(),
+                  unconstrained_client=synchronicity, secure=secure,
+                  categories=[SWEEP], channels=channels, outstanding=outstanding)
 
   def __str__(self):
     return 'c++'
diff --git a/tools/run_tests/pre_build_csharp.bat b/tools/run_tests/pre_build_csharp.bat
index 580d563..f15979a 100644
--- a/tools/run_tests/pre_build_csharp.bat
+++ b/tools/run_tests/pre_build_csharp.bat
@@ -38,9 +38,10 @@
 set NUGET=C:\nuget\nuget.exe
 
 if exist %NUGET% (
+  @rem TODO(jtattermusch): Get rid of this hack. See #8034
   @rem Restore Grpc packages by packages since Nuget client 3.4.4 doesnt support restore
   @rem by solution
-  @rem Moving into each directory to let the restores work with both nuget 3.4 and 2.8
+  @rem Moving into each directory to let the restores work based on per-project packages.config files
   %NUGET% restore vsprojects/grpc_csharp_ext.sln || goto :error
 
   cd src/csharp
diff --git a/tools/run_tests/pre_build_csharp.sh b/tools/run_tests/pre_build_csharp.sh
index 0fd3b92..ee678dd 100755
--- a/tools/run_tests/pre_build_csharp.sh
+++ b/tools/run_tests/pre_build_csharp.sh
@@ -37,9 +37,10 @@
 
 if [ -x "$(command -v nuget)" ]
 then
+  # TODO(jtattermusch): Get rid of this hack. See #8034
   # Restoring Nuget packages by packages rather than by solution because of
   # inability to restore by solution with Nuget client 3.4.4
-  # Moving into each directory to let the restores work with nuget 3.4 and 2.8
+  # Moving into each directory to let the restores work based on per-project packages.config files
   cd Grpc.Auth
   nuget restore -PackagesDirectory ../packages
   cd ..
diff --git a/tools/run_tests/run_build_statistics.py b/tools/run_tests/run_build_statistics.py
index df155f8..89aad2a 100755
--- a/tools/run_tests/run_build_statistics.py
+++ b/tools/run_tests/run_build_statistics.py
@@ -64,7 +64,7 @@
     'Failed to build workspace Tests with scheme AllTests',
     'Build timed out',
     'FATAL: Unable to produce a script file',
-    'FAILED: build_docker_c++',
+    'FAILED: build_docker_c\+\+',
     'cannot find package \"cloud.google.com/go/compute/metadata\"',
     'LLVM ERROR: IO failure on output stream.',
     'MSBUILD : error MSB1009: Project file does not exist.',
@@ -72,6 +72,7 @@
     'Failed to fetch from http://github.com/grpc/grpc.git',
     ('hudson.remoting.RemotingSystemException: java.io.IOException: '
      'Backing channel is disconnected.'),
+    'hudson.remoting.ChannelClosedException',
     'FAILED: bins/tsan/qps_openloop_test GRPC_POLL_STRATEGY=epoll',
     'FAILED: bins/tsan/qps_openloop_test GRPC_POLL_STRATEGY=legacy',
     'FAILED: bins/tsan/qps_openloop_test GRPC_POLL_STRATEGY=poll',
diff --git a/tools/run_tests/run_performance_tests.py b/tools/run_tests/run_performance_tests.py
index 25f5d46..3f028f1 100755
--- a/tools/run_tests/run_performance_tests.py
+++ b/tools/run_tests/run_performance_tests.py
@@ -33,11 +33,13 @@
 from __future__ import print_function
 
 import argparse
+import collections
 import itertools
 import jobset
 import json
 import multiprocessing
 import os
+import performance.scenario_config as scenario_config
 import pipes
 import re
 import subprocess
@@ -46,7 +48,6 @@
 import time
 import traceback
 import uuid
-import performance.scenario_config as scenario_config
 
 
 _ROOT = os.path.abspath(os.path.join(os.path.dirname(sys.argv[0]), '../..'))
@@ -63,14 +64,19 @@
     self._spec = spec
     self.language = language
     self.host_and_port = host_and_port
-    self._job = jobset.Job(spec, newline_on_success=True, travis=True, add_env={})
+    self._job = None
+
+  def start(self):
+    self._job = jobset.Job(self._spec, newline_on_success=True, travis=True, add_env={})
 
   def is_running(self):
     """Polls a job and returns True if given job is still running."""
-    return self._job.state() == jobset._RUNNING
+    return self._job and self._job.state() == jobset._RUNNING
 
   def kill(self):
-    return self._job.kill()
+    if self._job:
+      self._job.kill()
+      self._job = None
 
 
 def create_qpsworker_job(language, shortname=None,
@@ -119,7 +125,7 @@
 def create_quit_jobspec(workers, remote_host=None):
   """Runs quit using QPS driver."""
   # setting QPS_WORKERS env variable here makes sure it works with SSH too.
-  cmd = 'QPS_WORKERS="%s" bins/opt/qps_json_driver --quit' % ','.join(workers)
+  cmd = 'QPS_WORKERS="%s" bins/opt/qps_json_driver --quit' % ','.join(w.host_and_port for w in workers)
   if remote_host:
     user_at_host = '%s@%s' % (_REMOTE_HOST_USERNAME, remote_host)
     cmd = 'ssh %s "cd ~/performance_workspace/grpc/ && "%s' % (user_at_host, pipes.quote(cmd))
@@ -253,8 +259,8 @@
     sys.exit(1)
 
 
-def start_qpsworkers(languages, worker_hosts):
-  """Starts QPS workers as background jobs."""
+def create_qpsworkers(languages, worker_hosts):
+  """Creates QPS workers (but does not start them)."""
   if not worker_hosts:
     # run two workers locally (for each language)
     workers=[(None, 10000), (None, 10010)]
@@ -274,6 +280,9 @@
           for worker_idx, worker in enumerate(workers)]
 
 
+Scenario = collections.namedtuple('Scenario', 'jobspec workers')
+
+
 def create_scenarios(languages, workers_by_lang, remote_host=None, regex='.*',
                      category='all', bq_result_table=None,
                      netperf=False, netperf_hosts=[]):
@@ -282,6 +291,7 @@
                  for workers in workers_by_lang.values()
                  for worker in workers]
   scenarios = []
+  _NO_WORKERS = []
 
   if netperf:
     if not netperf_hosts:
@@ -293,16 +303,18 @@
     else:
       netperf_server=netperf_hosts[0]
       netperf_client=netperf_hosts[1]
-    scenarios.append(create_netperf_jobspec(server_host=netperf_server,
-                                            client_host=netperf_client,
-                                            bq_result_table=bq_result_table))
+    scenarios.append(Scenario(
+        create_netperf_jobspec(server_host=netperf_server,
+                               client_host=netperf_client,
+                               bq_result_table=bq_result_table),
+        _NO_WORKERS))
 
   for language in languages:
     for scenario_json in language.scenarios():
       if re.search(args.regex, scenario_json['name']):
-        categories = scenario_json.get('CATEGORIES', [])
-        if category in categories or (category == 'all' and categories != ['sweep']):
-          workers = workers_by_lang[str(language)]
+        categories = scenario_json.get('CATEGORIES', ['scalable', 'smoketest'])
+        if category in categories or category == 'all':
+          workers = workers_by_lang[str(language)][:]
           # 'SERVER_LANGUAGE' is an indicator for this script to pick
           # a server in different language.
           custom_server_lang = scenario_json.get('SERVER_LANGUAGE', None)
@@ -330,14 +342,14 @@
               # replace all client workers by workers of a different language,
               # leave num_server workers as they are server workers.
               workers[idx] = workers_by_lang[custom_client_lang][idx]
-          scenario = create_scenario_jobspec(scenario_json,
-                                             workers,
-                                             remote_host=remote_host,
-                                             bq_result_table=bq_result_table)
+          scenario = Scenario(
+              create_scenario_jobspec(scenario_json,
+                                      [w.host_and_port for w in workers],
+                                      remote_host=remote_host,
+                                      bq_result_table=bq_result_table),
+              workers)
           scenarios.append(scenario)
 
-  # the very last scenario requests shutting down the workers.
-  scenarios.append(create_quit_jobspec(all_workers, remote_host=remote_host))
   return scenarios
 
 
@@ -411,42 +423,31 @@
   build_local = True
 build_on_remote_hosts(remote_hosts, languages=[str(l) for l in languages], build_local=build_local)
 
-qpsworker_jobs = start_qpsworkers(languages, args.remote_worker_host)
-
-# TODO(jtattermusch): see https://github.com/grpc/grpc/issues/6174
-time.sleep(5)
+qpsworker_jobs = create_qpsworkers(languages, args.remote_worker_host)
 
 # get list of worker addresses for each language.
-worker_addresses = dict([(str(language), []) for language in languages])
+workers_by_lang = dict([(str(language), []) for language in languages])
 for job in qpsworker_jobs:
-  worker_addresses[str(job.language)].append(job.host_and_port)
+  workers_by_lang[str(job.language)].append(job)
 
-try:
-  scenarios = create_scenarios(languages,
-                               workers_by_lang=worker_addresses,
-                               remote_host=args.remote_driver_host,
-                               regex=args.regex,
-                               category=args.category,
-                               bq_result_table=args.bq_result_table,
-                               netperf=args.netperf,
-                               netperf_hosts=args.remote_worker_host)
+scenarios = create_scenarios(languages,
+                           workers_by_lang=workers_by_lang,
+                           remote_host=args.remote_driver_host,
+                           regex=args.regex,
+                           category=args.category,
+                           bq_result_table=args.bq_result_table,
+                           netperf=args.netperf,
+                           netperf_hosts=args.remote_worker_host)
 
-  if not scenarios:
-    raise Exception('No scenarios to run')
+if not scenarios:
+  raise Exception('No scenarios to run')
 
-  jobset.message('START', 'Running scenarios.', do_newline=True)
-  num_failures, _ = jobset.run(
-      scenarios, newline_on_success=True, maxjobs=1)
-  if num_failures == 0:
-    jobset.message('SUCCESS',
-                   'All scenarios finished successfully.',
-                   do_newline=True)
-  else:
-    jobset.message('FAILED', 'Some of the scenarios failed.',
-                   do_newline=True)
-    sys.exit(1)
-except:
-  traceback.print_exc()
-  raise
-finally:
-  finish_qps_workers(qpsworker_jobs)
+for scenario in scenarios:
+  try:
+    for worker in scenario.workers:
+      worker.start()
+    jobset.run([scenario.jobspec,
+                create_quit_jobspec(scenario.workers, remote_host=args.remote_driver_host)],
+               newline_on_success=True, maxjobs=1)
+  finally:
+    finish_qps_workers(scenario.workers)
diff --git a/tools/run_tests/sanity/check_submodules.sh b/tools/run_tests/sanity/check_submodules.sh
index 5562d33..f1d9d5a 100755
--- a/tools/run_tests/sanity/check_submodules.sh
+++ b/tools/run_tests/sanity/check_submodules.sh
@@ -44,7 +44,7 @@
  c880e42ba1c8032d4cdde2aba0541d8a9d9fa2e9 third_party/boringssl (version_for_cocoapods_2.0-100-gc880e42)
  05b155ff59114735ec8cd089f669c4c3d8f59029 third_party/gflags (v2.1.0-45-g05b155f)
  c99458533a9b4c743ed51537e25989ea55944908 third_party/googletest (release-1.7.0)
- f8ac463766281625ad710900479130c7fcb4d63b third_party/nanopb (nanopb-0.3.4-29-gf8ac463)
+ 68a86e96481e6bea987df8de47027847b30c325b third_party/nanopb (nanopb-0.3.6-6-g68a86e9)
  bba446bbf2ac7b0b9923d4eb07d5acd0665a8cf0 third_party/protobuf (v3.0.0-beta-4-160-gbba446b)
  50893291621658f355bc5b4d450a8d06a563053d third_party/zlib (v1.2.8)
  bcad91771b7f0bff28a1cac1981d7ef2b9bcef3c third_party/thrift
diff --git a/tools/run_tests/sources_and_headers.json b/tools/run_tests/sources_and_headers.json
index 3df07dc..447dbe4 100644
--- a/tools/run_tests/sources_and_headers.json
+++ b/tools/run_tests/sources_and_headers.json
@@ -261,6 +261,22 @@
     ], 
     "headers": [], 
     "language": "c", 
+    "name": "combiner_test", 
+    "src": [
+      "test/core/iomgr/combiner_test.c"
+    ], 
+    "third_party": false, 
+    "type": "target"
+  }, 
+  {
+    "deps": [
+      "gpr", 
+      "gpr_test_util", 
+      "grpc", 
+      "grpc_test_util"
+    ], 
+    "headers": [], 
+    "language": "c", 
     "name": "compression_test", 
     "src": [
       "test/core/compression/compression_test.c"
@@ -631,6 +647,20 @@
     ], 
     "headers": [], 
     "language": "c", 
+    "name": "gpr_mpscq_test", 
+    "src": [
+      "test/core/support/mpscq_test.c"
+    ], 
+    "third_party": false, 
+    "type": "target"
+  }, 
+  {
+    "deps": [
+      "gpr", 
+      "gpr_test_util"
+    ], 
+    "headers": [], 
+    "language": "c", 
     "name": "gpr_percent_encoding_test", 
     "src": [
       "test/core/support/percent_encoding_test.c"
@@ -5735,6 +5765,7 @@
       "src/core/lib/support/backoff.h", 
       "src/core/lib/support/block_annotate.h", 
       "src/core/lib/support/env.h", 
+      "src/core/lib/support/mpscq.h", 
       "src/core/lib/support/murmur_hash.h", 
       "src/core/lib/support/percent_encoding.h", 
       "src/core/lib/support/stack_lockfree.h", 
@@ -5799,6 +5830,8 @@
       "src/core/lib/support/log_linux.c", 
       "src/core/lib/support/log_posix.c", 
       "src/core/lib/support/log_windows.c", 
+      "src/core/lib/support/mpscq.c", 
+      "src/core/lib/support/mpscq.h", 
       "src/core/lib/support/murmur_hash.c", 
       "src/core/lib/support/murmur_hash.h", 
       "src/core/lib/support/percent_encoding.c", 
@@ -5899,6 +5932,7 @@
       "src/core/lib/http/httpcli.h", 
       "src/core/lib/http/parser.h", 
       "src/core/lib/iomgr/closure.h", 
+      "src/core/lib/iomgr/combiner.h", 
       "src/core/lib/iomgr/endpoint.h", 
       "src/core/lib/iomgr/endpoint_pair.h", 
       "src/core/lib/iomgr/error.h", 
@@ -6005,6 +6039,8 @@
       "src/core/lib/http/parser.h", 
       "src/core/lib/iomgr/closure.c", 
       "src/core/lib/iomgr/closure.h", 
+      "src/core/lib/iomgr/combiner.c", 
+      "src/core/lib/iomgr/combiner.h", 
       "src/core/lib/iomgr/endpoint.c", 
       "src/core/lib/iomgr/endpoint.h", 
       "src/core/lib/iomgr/endpoint_pair.h", 
@@ -6860,6 +6896,7 @@
       "include/grpc++/impl/codegen/service_type.h", 
       "include/grpc++/impl/codegen/status.h", 
       "include/grpc++/impl/codegen/status_code_enum.h", 
+      "include/grpc++/impl/codegen/status_helper.h", 
       "include/grpc++/impl/codegen/string_ref.h", 
       "include/grpc++/impl/codegen/stub_options.h", 
       "include/grpc++/impl/codegen/sync.h", 
@@ -6894,6 +6931,7 @@
       "include/grpc++/impl/codegen/service_type.h", 
       "include/grpc++/impl/codegen/status.h", 
       "include/grpc++/impl/codegen/status_code_enum.h", 
+      "include/grpc++/impl/codegen/status_helper.h", 
       "include/grpc++/impl/codegen/string_ref.h", 
       "include/grpc++/impl/codegen/stub_options.h", 
       "include/grpc++/impl/codegen/sync.h", 
diff --git a/tools/run_tests/tests.json b/tools/run_tests/tests.json
index cbc8f58..f9300c1 100644
--- a/tools/run_tests/tests.json
+++ b/tools/run_tests/tests.json
@@ -303,6 +303,27 @@
       "posix", 
       "windows"
     ], 
+    "cpu_cost": 30, 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "gtest": false, 
+    "language": "c", 
+    "name": "combiner_test", 
+    "platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ]
+  }, 
+  {
+    "args": [], 
+    "ci_platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
     "cpu_cost": 1.0, 
     "exclude_configs": [], 
     "flaky": false, 
@@ -705,6 +726,27 @@
       "posix", 
       "windows"
     ], 
+    "cpu_cost": 30, 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "gtest": false, 
+    "language": "c", 
+    "name": "gpr_mpscq_test", 
+    "platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ]
+  }, 
+  {
+    "args": [], 
+    "ci_platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
     "cpu_cost": 1.0, 
     "exclude_configs": [], 
     "flaky": false, 
@@ -29760,7 +29802,7 @@
   {
     "args": [
       "--scenarios_json", 
-      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_secure_1_channels\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"ASYNC_SERVER\"}, \"client_config\": {\"client_type\": \"ASYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 1, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 1000, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_secure_1_channels_1_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"SYNC_SERVER\"}, \"client_config\": {\"client_type\": \"SYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 1, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 1, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
     ], 
     "boringssl": true, 
     "ci_platforms": [
@@ -29781,13 +29823,13 @@
       "posix", 
       "windows"
     ], 
-    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_secure_1_channels", 
+    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_secure_1_channels_1_outstanding", 
     "timeout_seconds": 180
   }, 
   {
     "args": [
       "--scenarios_json", 
-      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_secure_3_channels\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"ASYNC_SERVER\"}, \"client_config\": {\"client_type\": \"ASYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 3, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 334, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_secure_1_channels_3_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"SYNC_SERVER\"}, \"client_config\": {\"client_type\": \"SYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 1, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 3, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
     ], 
     "boringssl": true, 
     "ci_platforms": [
@@ -29808,13 +29850,13 @@
       "posix", 
       "windows"
     ], 
-    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_secure_3_channels", 
+    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_secure_1_channels_3_outstanding", 
     "timeout_seconds": 180
   }, 
   {
     "args": [
       "--scenarios_json", 
-      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_secure_10_channels\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"ASYNC_SERVER\"}, \"client_config\": {\"client_type\": \"ASYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 10, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 100, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_secure_1_channels_10_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"SYNC_SERVER\"}, \"client_config\": {\"client_type\": \"SYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 1, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 10, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
     ], 
     "boringssl": true, 
     "ci_platforms": [
@@ -29835,13 +29877,13 @@
       "posix", 
       "windows"
     ], 
-    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_secure_10_channels", 
+    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_secure_1_channels_10_outstanding", 
     "timeout_seconds": 180
   }, 
   {
     "args": [
       "--scenarios_json", 
-      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_secure_31_channels\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"ASYNC_SERVER\"}, \"client_config\": {\"client_type\": \"ASYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 31, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 33, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_secure_1_channels_32_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"SYNC_SERVER\"}, \"client_config\": {\"client_type\": \"SYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 1, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 32, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
     ], 
     "boringssl": true, 
     "ci_platforms": [
@@ -29862,13 +29904,13 @@
       "posix", 
       "windows"
     ], 
-    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_secure_31_channels", 
+    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_secure_1_channels_32_outstanding", 
     "timeout_seconds": 180
   }, 
   {
     "args": [
       "--scenarios_json", 
-      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_secure_100_channels\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"ASYNC_SERVER\"}, \"client_config\": {\"client_type\": \"ASYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 100, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 10, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_secure_1_channels_100_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"SYNC_SERVER\"}, \"client_config\": {\"client_type\": \"SYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 1, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 100, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
     ], 
     "boringssl": true, 
     "ci_platforms": [
@@ -29889,13 +29931,13 @@
       "posix", 
       "windows"
     ], 
-    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_secure_100_channels", 
+    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_secure_1_channels_100_outstanding", 
     "timeout_seconds": 180
   }, 
   {
     "args": [
       "--scenarios_json", 
-      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_secure_316_channels\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"ASYNC_SERVER\"}, \"client_config\": {\"client_type\": \"ASYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 316, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 4, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_secure_1_channels_316_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"SYNC_SERVER\"}, \"client_config\": {\"client_type\": \"SYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 1, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 316, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
     ], 
     "boringssl": true, 
     "ci_platforms": [
@@ -29916,13 +29958,13 @@
       "posix", 
       "windows"
     ], 
-    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_secure_316_channels", 
+    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_secure_1_channels_316_outstanding", 
     "timeout_seconds": 180
   }, 
   {
     "args": [
       "--scenarios_json", 
-      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_secure_1000_channels\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"ASYNC_SERVER\"}, \"client_config\": {\"client_type\": \"ASYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 1000, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 1, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_secure_1_channels_1000_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"SYNC_SERVER\"}, \"client_config\": {\"client_type\": \"SYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 1, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 1000, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
     ], 
     "boringssl": true, 
     "ci_platforms": [
@@ -29943,7 +29985,547 @@
       "posix", 
       "windows"
     ], 
-    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_secure_1000_channels", 
+    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_secure_1_channels_1000_outstanding", 
+    "timeout_seconds": 180
+  }, 
+  {
+    "args": [
+      "--scenarios_json", 
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_secure_3_channels_3_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"SYNC_SERVER\"}, \"client_config\": {\"client_type\": \"SYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 3, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 1, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+    ], 
+    "boringssl": true, 
+    "ci_platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "cpu_cost": 8, 
+    "defaults": "boringssl", 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c++", 
+    "name": "json_run_localhost", 
+    "platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_secure_3_channels_3_outstanding", 
+    "timeout_seconds": 180
+  }, 
+  {
+    "args": [
+      "--scenarios_json", 
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_secure_3_channels_10_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"SYNC_SERVER\"}, \"client_config\": {\"client_type\": \"SYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 3, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 4, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+    ], 
+    "boringssl": true, 
+    "ci_platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "cpu_cost": 8, 
+    "defaults": "boringssl", 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c++", 
+    "name": "json_run_localhost", 
+    "platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_secure_3_channels_10_outstanding", 
+    "timeout_seconds": 180
+  }, 
+  {
+    "args": [
+      "--scenarios_json", 
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_secure_3_channels_32_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"SYNC_SERVER\"}, \"client_config\": {\"client_type\": \"SYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 3, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 11, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+    ], 
+    "boringssl": true, 
+    "ci_platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "cpu_cost": 8, 
+    "defaults": "boringssl", 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c++", 
+    "name": "json_run_localhost", 
+    "platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_secure_3_channels_32_outstanding", 
+    "timeout_seconds": 180
+  }, 
+  {
+    "args": [
+      "--scenarios_json", 
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_secure_3_channels_100_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"SYNC_SERVER\"}, \"client_config\": {\"client_type\": \"SYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 3, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 34, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+    ], 
+    "boringssl": true, 
+    "ci_platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "cpu_cost": 8, 
+    "defaults": "boringssl", 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c++", 
+    "name": "json_run_localhost", 
+    "platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_secure_3_channels_100_outstanding", 
+    "timeout_seconds": 180
+  }, 
+  {
+    "args": [
+      "--scenarios_json", 
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_secure_3_channels_316_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"SYNC_SERVER\"}, \"client_config\": {\"client_type\": \"SYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 3, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 106, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+    ], 
+    "boringssl": true, 
+    "ci_platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "cpu_cost": 8, 
+    "defaults": "boringssl", 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c++", 
+    "name": "json_run_localhost", 
+    "platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_secure_3_channels_316_outstanding", 
+    "timeout_seconds": 180
+  }, 
+  {
+    "args": [
+      "--scenarios_json", 
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_secure_3_channels_1000_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"SYNC_SERVER\"}, \"client_config\": {\"client_type\": \"SYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 3, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 334, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+    ], 
+    "boringssl": true, 
+    "ci_platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "cpu_cost": 8, 
+    "defaults": "boringssl", 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c++", 
+    "name": "json_run_localhost", 
+    "platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_secure_3_channels_1000_outstanding", 
+    "timeout_seconds": 180
+  }, 
+  {
+    "args": [
+      "--scenarios_json", 
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_secure_10_channels_10_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"SYNC_SERVER\"}, \"client_config\": {\"client_type\": \"SYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 10, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 1, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+    ], 
+    "boringssl": true, 
+    "ci_platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "cpu_cost": 8, 
+    "defaults": "boringssl", 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c++", 
+    "name": "json_run_localhost", 
+    "platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_secure_10_channels_10_outstanding", 
+    "timeout_seconds": 180
+  }, 
+  {
+    "args": [
+      "--scenarios_json", 
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_secure_10_channels_32_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"SYNC_SERVER\"}, \"client_config\": {\"client_type\": \"SYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 10, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 4, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+    ], 
+    "boringssl": true, 
+    "ci_platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "cpu_cost": 8, 
+    "defaults": "boringssl", 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c++", 
+    "name": "json_run_localhost", 
+    "platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_secure_10_channels_32_outstanding", 
+    "timeout_seconds": 180
+  }, 
+  {
+    "args": [
+      "--scenarios_json", 
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+      "linux", 
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+      "windows"
+    ], 
+    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_secure_10_channels_100_outstanding", 
+    "timeout_seconds": 180
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+    ], 
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+    "timeout_seconds": 180
+  }, 
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+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_secure_10_channels_1000_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"SYNC_SERVER\"}, \"client_config\": {\"client_type\": \"SYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 10, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 100, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
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+    ], 
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+    "timeout_seconds": 180
+  }, 
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+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_secure_32_channels_32_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"SYNC_SERVER\"}, \"client_config\": {\"client_type\": \"SYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 32, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 1, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
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+    ], 
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+    "defaults": "boringssl", 
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+      "linux", 
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+      "posix", 
+      "windows"
+    ], 
+    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_secure_32_channels_32_outstanding", 
+    "timeout_seconds": 180
+  }, 
+  {
+    "args": [
+      "--scenarios_json", 
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_secure_32_channels_100_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"SYNC_SERVER\"}, \"client_config\": {\"client_type\": \"SYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 32, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 4, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+    ], 
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+    "ci_platforms": [
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+    "platforms": [
+      "linux", 
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+      "posix", 
+      "windows"
+    ], 
+    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_secure_32_channels_100_outstanding", 
+    "timeout_seconds": 180
+  }, 
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+    "args": [
+      "--scenarios_json", 
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_secure_32_channels_316_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"SYNC_SERVER\"}, \"client_config\": {\"client_type\": \"SYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 32, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 10, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+    ], 
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+    "ci_platforms": [
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+    ], 
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+    "defaults": "boringssl", 
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+    "flaky": false, 
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+    "name": "json_run_localhost", 
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+      "linux", 
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+      "posix", 
+      "windows"
+    ], 
+    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_secure_32_channels_316_outstanding", 
+    "timeout_seconds": 180
+  }, 
+  {
+    "args": [
+      "--scenarios_json", 
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_secure_32_channels_1000_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"SYNC_SERVER\"}, \"client_config\": {\"client_type\": \"SYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 32, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 32, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+    ], 
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+    "ci_platforms": [
+      "linux", 
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+      "posix", 
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+    ], 
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+    "defaults": "boringssl", 
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+    "flaky": false, 
+    "language": "c++", 
+    "name": "json_run_localhost", 
+    "platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_secure_32_channels_1000_outstanding", 
+    "timeout_seconds": 180
+  }, 
+  {
+    "args": [
+      "--scenarios_json", 
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_secure_100_channels_100_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"SYNC_SERVER\"}, \"client_config\": {\"client_type\": \"SYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 100, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 1, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+    ], 
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+    "ci_platforms": [
+      "linux", 
+      "mac", 
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+    ], 
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+    "name": "json_run_localhost", 
+    "platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_secure_100_channels_100_outstanding", 
+    "timeout_seconds": 180
+  }, 
+  {
+    "args": [
+      "--scenarios_json", 
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_secure_100_channels_316_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"SYNC_SERVER\"}, \"client_config\": {\"client_type\": \"SYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 100, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 4, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+    ], 
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+    "ci_platforms": [
+      "linux", 
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+    ], 
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+    "defaults": "boringssl", 
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+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_secure_100_channels_316_outstanding", 
+    "timeout_seconds": 180
+  }, 
+  {
+    "args": [
+      "--scenarios_json", 
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_secure_100_channels_1000_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"SYNC_SERVER\"}, \"client_config\": {\"client_type\": \"SYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 100, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 10, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+    ], 
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+    "ci_platforms": [
+      "linux", 
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+      "windows"
+    ], 
+    "cpu_cost": 8, 
+    "defaults": "boringssl", 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c++", 
+    "name": "json_run_localhost", 
+    "platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_secure_100_channels_1000_outstanding", 
+    "timeout_seconds": 180
+  }, 
+  {
+    "args": [
+      "--scenarios_json", 
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_secure_316_channels_316_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"SYNC_SERVER\"}, \"client_config\": {\"client_type\": \"SYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 316, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 1, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+    ], 
+    "boringssl": true, 
+    "ci_platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "cpu_cost": 8, 
+    "defaults": "boringssl", 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c++", 
+    "name": "json_run_localhost", 
+    "platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_secure_316_channels_316_outstanding", 
+    "timeout_seconds": 180
+  }, 
+  {
+    "args": [
+      "--scenarios_json", 
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_secure_316_channels_1000_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"SYNC_SERVER\"}, \"client_config\": {\"client_type\": \"SYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 316, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 4, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+    ], 
+    "boringssl": true, 
+    "ci_platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "cpu_cost": 8, 
+    "defaults": "boringssl", 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c++", 
+    "name": "json_run_localhost", 
+    "platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_secure_316_channels_1000_outstanding", 
     "timeout_seconds": 180
   }, 
   {
@@ -30057,7 +30639,7 @@
   {
     "args": [
       "--scenarios_json", 
-      "{\"scenarios\": [{\"name\": \"cpp_protobuf_async_unary_qps_unconstrained_secure_1_channels\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"ASYNC_SERVER\"}, \"client_config\": {\"client_type\": \"ASYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 1, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 6400, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_async_unary_qps_unconstrained_secure_1_channels_1_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"ASYNC_SERVER\"}, \"client_config\": {\"client_type\": \"ASYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 1, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 1, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
     ], 
     "boringssl": true, 
     "ci_platforms": [
@@ -30078,13 +30660,13 @@
       "posix", 
       "windows"
     ], 
-    "shortname": "json_run_localhost:cpp_protobuf_async_unary_qps_unconstrained_secure_1_channels", 
+    "shortname": "json_run_localhost:cpp_protobuf_async_unary_qps_unconstrained_secure_1_channels_1_outstanding", 
     "timeout_seconds": 180
   }, 
   {
     "args": [
       "--scenarios_json", 
-      "{\"scenarios\": [{\"name\": \"cpp_protobuf_async_unary_qps_unconstrained_secure_3_channels\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"ASYNC_SERVER\"}, \"client_config\": {\"client_type\": \"ASYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 3, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 2134, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_async_unary_qps_unconstrained_secure_1_channels_3_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"ASYNC_SERVER\"}, \"client_config\": {\"client_type\": \"ASYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 1, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 3, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
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@@ -30105,13 +30687,13 @@
       "posix", 
       "windows"
     ], 
-    "shortname": "json_run_localhost:cpp_protobuf_async_unary_qps_unconstrained_secure_3_channels", 
+    "shortname": "json_run_localhost:cpp_protobuf_async_unary_qps_unconstrained_secure_1_channels_3_outstanding", 
     "timeout_seconds": 180
   }, 
   {
     "args": [
       "--scenarios_json", 
-      "{\"scenarios\": [{\"name\": \"cpp_protobuf_async_unary_qps_unconstrained_secure_10_channels\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"ASYNC_SERVER\"}, \"client_config\": {\"client_type\": \"ASYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 10, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 640, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_async_unary_qps_unconstrained_secure_1_channels_10_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"ASYNC_SERVER\"}, \"client_config\": {\"client_type\": \"ASYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 1, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 10, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
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     "ci_platforms": [
@@ -30132,13 +30714,13 @@
       "posix", 
       "windows"
     ], 
-    "shortname": "json_run_localhost:cpp_protobuf_async_unary_qps_unconstrained_secure_10_channels", 
+    "shortname": "json_run_localhost:cpp_protobuf_async_unary_qps_unconstrained_secure_1_channels_10_outstanding", 
     "timeout_seconds": 180
   }, 
   {
     "args": [
       "--scenarios_json", 
-      "{\"scenarios\": [{\"name\": \"cpp_protobuf_async_unary_qps_unconstrained_secure_31_channels\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"ASYNC_SERVER\"}, \"client_config\": {\"client_type\": \"ASYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 31, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 207, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_async_unary_qps_unconstrained_secure_1_channels_32_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"ASYNC_SERVER\"}, \"client_config\": {\"client_type\": \"ASYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 1, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 32, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
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     "boringssl": true, 
     "ci_platforms": [
@@ -30159,13 +30741,13 @@
       "posix", 
       "windows"
     ], 
-    "shortname": "json_run_localhost:cpp_protobuf_async_unary_qps_unconstrained_secure_31_channels", 
+    "shortname": "json_run_localhost:cpp_protobuf_async_unary_qps_unconstrained_secure_1_channels_32_outstanding", 
     "timeout_seconds": 180
   }, 
   {
     "args": [
       "--scenarios_json", 
-      "{\"scenarios\": [{\"name\": \"cpp_protobuf_async_unary_qps_unconstrained_secure_100_channels\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"ASYNC_SERVER\"}, \"client_config\": {\"client_type\": \"ASYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 100, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 64, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_async_unary_qps_unconstrained_secure_1_channels_100_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"ASYNC_SERVER\"}, \"client_config\": {\"client_type\": \"ASYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 1, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 100, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
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     "boringssl": true, 
     "ci_platforms": [
@@ -30186,13 +30768,13 @@
       "posix", 
       "windows"
     ], 
-    "shortname": "json_run_localhost:cpp_protobuf_async_unary_qps_unconstrained_secure_100_channels", 
+    "shortname": "json_run_localhost:cpp_protobuf_async_unary_qps_unconstrained_secure_1_channels_100_outstanding", 
     "timeout_seconds": 180
   }, 
   {
     "args": [
       "--scenarios_json", 
-      "{\"scenarios\": [{\"name\": \"cpp_protobuf_async_unary_qps_unconstrained_secure_316_channels\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"ASYNC_SERVER\"}, \"client_config\": {\"client_type\": \"ASYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 316, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 21, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_async_unary_qps_unconstrained_secure_1_channels_316_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"ASYNC_SERVER\"}, \"client_config\": {\"client_type\": \"ASYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 1, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 316, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
     ], 
     "boringssl": true, 
     "ci_platforms": [
@@ -30213,13 +30795,13 @@
       "posix", 
       "windows"
     ], 
-    "shortname": "json_run_localhost:cpp_protobuf_async_unary_qps_unconstrained_secure_316_channels", 
+    "shortname": "json_run_localhost:cpp_protobuf_async_unary_qps_unconstrained_secure_1_channels_316_outstanding", 
     "timeout_seconds": 180
   }, 
   {
     "args": [
       "--scenarios_json", 
-      "{\"scenarios\": [{\"name\": \"cpp_protobuf_async_unary_qps_unconstrained_secure_1000_channels\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"ASYNC_SERVER\"}, \"client_config\": {\"client_type\": \"ASYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 1000, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 7, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_async_unary_qps_unconstrained_secure_1_channels_1000_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"ASYNC_SERVER\"}, \"client_config\": {\"client_type\": \"ASYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 1, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 1000, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
     ], 
     "boringssl": true, 
     "ci_platforms": [
@@ -30240,7 +30822,871 @@
       "posix", 
       "windows"
     ], 
-    "shortname": "json_run_localhost:cpp_protobuf_async_unary_qps_unconstrained_secure_1000_channels", 
+    "shortname": "json_run_localhost:cpp_protobuf_async_unary_qps_unconstrained_secure_1_channels_1000_outstanding", 
+    "timeout_seconds": 180
+  }, 
+  {
+    "args": [
+      "--scenarios_json", 
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_async_unary_qps_unconstrained_secure_1_channels_3162_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"ASYNC_SERVER\"}, \"client_config\": {\"client_type\": \"ASYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 1, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 3162, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+    ], 
+    "boringssl": true, 
+    "ci_platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "cpu_cost": 8, 
+    "defaults": "boringssl", 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c++", 
+    "name": "json_run_localhost", 
+    "platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "shortname": "json_run_localhost:cpp_protobuf_async_unary_qps_unconstrained_secure_1_channels_3162_outstanding", 
+    "timeout_seconds": 180
+  }, 
+  {
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+      "--scenarios_json", 
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_async_unary_qps_unconstrained_secure_1_channels_10000_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"ASYNC_SERVER\"}, \"client_config\": {\"client_type\": \"ASYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 1, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 10000, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+    ], 
+    "boringssl": true, 
+    "ci_platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "cpu_cost": 8, 
+    "defaults": "boringssl", 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c++", 
+    "name": "json_run_localhost", 
+    "platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "shortname": "json_run_localhost:cpp_protobuf_async_unary_qps_unconstrained_secure_1_channels_10000_outstanding", 
+    "timeout_seconds": 180
+  }, 
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+      "--scenarios_json", 
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_async_unary_qps_unconstrained_secure_3_channels_3_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"ASYNC_SERVER\"}, \"client_config\": {\"client_type\": \"ASYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 3, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 1, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+    ], 
+    "boringssl": true, 
+    "ci_platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "cpu_cost": 8, 
+    "defaults": "boringssl", 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c++", 
+    "name": "json_run_localhost", 
+    "platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "shortname": "json_run_localhost:cpp_protobuf_async_unary_qps_unconstrained_secure_3_channels_3_outstanding", 
+    "timeout_seconds": 180
+  }, 
+  {
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+      "--scenarios_json", 
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_async_unary_qps_unconstrained_secure_3_channels_10_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"ASYNC_SERVER\"}, \"client_config\": {\"client_type\": \"ASYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 3, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 4, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+    ], 
+    "boringssl": true, 
+    "ci_platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "cpu_cost": 8, 
+    "defaults": "boringssl", 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c++", 
+    "name": "json_run_localhost", 
+    "platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "shortname": "json_run_localhost:cpp_protobuf_async_unary_qps_unconstrained_secure_3_channels_10_outstanding", 
+    "timeout_seconds": 180
+  }, 
+  {
+    "args": [
+      "--scenarios_json", 
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_async_unary_qps_unconstrained_secure_3_channels_32_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"ASYNC_SERVER\"}, \"client_config\": {\"client_type\": \"ASYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 3, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 11, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+    ], 
+    "boringssl": true, 
+    "ci_platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "cpu_cost": 8, 
+    "defaults": "boringssl", 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c++", 
+    "name": "json_run_localhost", 
+    "platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "shortname": "json_run_localhost:cpp_protobuf_async_unary_qps_unconstrained_secure_3_channels_32_outstanding", 
+    "timeout_seconds": 180
+  }, 
+  {
+    "args": [
+      "--scenarios_json", 
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_async_unary_qps_unconstrained_secure_3_channels_100_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"ASYNC_SERVER\"}, \"client_config\": {\"client_type\": \"ASYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 3, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 34, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+    ], 
+    "boringssl": true, 
+    "ci_platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "cpu_cost": 8, 
+    "defaults": "boringssl", 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c++", 
+    "name": "json_run_localhost", 
+    "platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "shortname": "json_run_localhost:cpp_protobuf_async_unary_qps_unconstrained_secure_3_channels_100_outstanding", 
+    "timeout_seconds": 180
+  }, 
+  {
+    "args": [
+      "--scenarios_json", 
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_async_unary_qps_unconstrained_secure_3_channels_316_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"ASYNC_SERVER\"}, \"client_config\": {\"client_type\": \"ASYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 3, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 106, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+    ], 
+    "boringssl": true, 
+    "ci_platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "cpu_cost": 8, 
+    "defaults": "boringssl", 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c++", 
+    "name": "json_run_localhost", 
+    "platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "shortname": "json_run_localhost:cpp_protobuf_async_unary_qps_unconstrained_secure_3_channels_316_outstanding", 
+    "timeout_seconds": 180
+  }, 
+  {
+    "args": [
+      "--scenarios_json", 
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_async_unary_qps_unconstrained_secure_3_channels_1000_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"server_type\": \"ASYNC_SERVER\"}, \"client_config\": {\"client_type\": \"ASYNC_CLIENT\", \"security_params\": {\"use_test_ca\": true, \"server_host_override\": \"foo.test.google.fr\"}, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 3, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 334, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+    ], 
+    "boringssl": true, 
+    "ci_platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "cpu_cost": 8, 
+    "defaults": "boringssl", 
+    "exclude_configs": [], 
+    "flaky": false, 
+    "language": "c++", 
+    "name": "json_run_localhost", 
+    "platforms": [
+      "linux", 
+      "mac", 
+      "posix", 
+      "windows"
+    ], 
+    "shortname": "json_run_localhost:cpp_protobuf_async_unary_qps_unconstrained_secure_3_channels_1000_outstanding", 
+    "timeout_seconds": 180
+  }, 
+  {
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+    "timeout_seconds": 180
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+    ], 
+    "shortname": "json_run_localhost:cpp_protobuf_async_unary_qps_unconstrained_secure_316_channels_10000_outstanding", 
     "timeout_seconds": 180
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   {
@@ -30435,7 +31881,7 @@
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+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_insecure_1_channels_1_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": null, \"server_type\": \"SYNC_SERVER\"}, \"client_config\": {\"client_type\": \"SYNC_CLIENT\", \"security_params\": null, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 1, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 1, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
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@@ -30456,13 +31902,13 @@
       "posix", 
       "windows"
     ], 
-    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_insecure_1_channels", 
+    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_insecure_1_channels_1_outstanding", 
     "timeout_seconds": 180
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-      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_insecure_3_channels\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": null, \"server_type\": \"ASYNC_SERVER\"}, \"client_config\": {\"client_type\": \"ASYNC_CLIENT\", \"security_params\": null, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 3, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 334, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_insecure_1_channels_3_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": null, \"server_type\": \"SYNC_SERVER\"}, \"client_config\": {\"client_type\": \"SYNC_CLIENT\", \"security_params\": null, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 1, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 3, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
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@@ -30483,13 +31929,13 @@
       "posix", 
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-    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_insecure_3_channels", 
+    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_insecure_1_channels_3_outstanding", 
     "timeout_seconds": 180
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+      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_insecure_1_channels_10_outstanding\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": null, \"server_type\": \"SYNC_SERVER\"}, \"client_config\": {\"client_type\": \"SYNC_CLIENT\", \"security_params\": null, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 1, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 10, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
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@@ -30510,13 +31956,13 @@
       "posix", 
       "windows"
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-    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_insecure_10_channels", 
+    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_insecure_1_channels_10_outstanding", 
     "timeout_seconds": 180
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-      "{\"scenarios\": [{\"name\": \"cpp_protobuf_sync_unary_qps_unconstrained_insecure_31_channels\", \"warmup_seconds\": 0, \"benchmark_seconds\": 1, \"num_servers\": 1, \"server_config\": {\"async_server_threads\": 0, \"core_limit\": 0, \"security_params\": null, \"server_type\": \"ASYNC_SERVER\"}, \"client_config\": {\"client_type\": \"ASYNC_CLIENT\", \"security_params\": null, \"payload_config\": {\"simple_params\": {\"resp_size\": 0, \"req_size\": 0}}, \"client_channels\": 31, \"async_client_threads\": 0, \"outstanding_rpcs_per_channel\": 33, \"rpc_type\": \"UNARY\", \"load_params\": {\"closed_loop\": {}}, \"histogram_params\": {\"max_possible\": 60000000000.0, \"resolution\": 0.01}}, \"num_clients\": 0}]}"
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@@ -30537,13 +31983,13 @@
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-    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_insecure_31_channels", 
+    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_insecure_1_channels_32_outstanding", 
     "timeout_seconds": 180
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@@ -30564,13 +32010,13 @@
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-    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_insecure_100_channels", 
+    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_insecure_1_channels_100_outstanding", 
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@@ -30591,13 +32037,13 @@
       "posix", 
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-    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_insecure_316_channels", 
+    "shortname": "json_run_localhost:cpp_protobuf_sync_unary_qps_unconstrained_insecure_1_channels_316_outstanding", 
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@@ -30618,7 +32064,547 @@
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diff --git a/vsprojects/buildtests_c.sln b/vsprojects/buildtests_c.sln
index 8f3546f..04f4876 100644
--- a/vsprojects/buildtests_c.sln
+++ b/vsprojects/buildtests_c.sln
@@ -175,6 +175,17 @@
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 	EndProjectSection
 EndProject
+Project("{8BC9CEB8-8B4A-11D0-8D11-00A0C91BC942}") = "combiner_test", "vcxproj\test\combiner_test\combiner_test.vcxproj", "{C237D1E4-8825-80BA-1FC3-5E147E53E96E}"
+	ProjectSection(myProperties) = preProject
+        	lib = "False"
+	EndProjectSection
+	ProjectSection(ProjectDependencies) = postProject
+		{17BCAFC0-5FDC-4C94-AEB9-95F3E220614B} = {17BCAFC0-5FDC-4C94-AEB9-95F3E220614B}
+		{29D16885-7228-4C31-81ED-5F9187C7F2A9} = {29D16885-7228-4C31-81ED-5F9187C7F2A9}
+		{EAB0A629-17A9-44DB-B5FF-E91A721FE037} = {EAB0A629-17A9-44DB-B5FF-E91A721FE037}
+		{B23D3D1A-9438-4EDA-BEB6-9A0A03D17792} = {B23D3D1A-9438-4EDA-BEB6-9A0A03D17792}
+	EndProjectSection
+EndProject
 Project("{8BC9CEB8-8B4A-11D0-8D11-00A0C91BC942}") = "compression_test", "vcxproj\test\compression_test\compression_test.vcxproj", "{5AFE7D17-A4A7-D68E-4491-CBC852F9D2A0}"
 	ProjectSection(myProperties) = preProject
         	lib = "False"
@@ -382,6 +393,15 @@
 		{B23D3D1A-9438-4EDA-BEB6-9A0A03D17792} = {B23D3D1A-9438-4EDA-BEB6-9A0A03D17792}
 	EndProjectSection
 EndProject
+Project("{8BC9CEB8-8B4A-11D0-8D11-00A0C91BC942}") = "gpr_mpscq_test", "vcxproj\test\gpr_mpscq_test\gpr_mpscq_test.vcxproj", "{B3D7760B-8BEA-2EF6-F1D4-9F9020E166D6}"
+	ProjectSection(myProperties) = preProject
+        	lib = "False"
+	EndProjectSection
+	ProjectSection(ProjectDependencies) = postProject
+		{EAB0A629-17A9-44DB-B5FF-E91A721FE037} = {EAB0A629-17A9-44DB-B5FF-E91A721FE037}
+		{B23D3D1A-9438-4EDA-BEB6-9A0A03D17792} = {B23D3D1A-9438-4EDA-BEB6-9A0A03D17792}
+	EndProjectSection
+EndProject
 Project("{8BC9CEB8-8B4A-11D0-8D11-00A0C91BC942}") = "gpr_percent_encoding_test", "vcxproj\test\gpr_percent_encoding_test\gpr_percent_encoding_test.vcxproj", "{8313AE17-FCFA-8110-95C7-7AF2F814D188}"
 	ProjectSection(myProperties) = preProject
         	lib = "False"
@@ -1720,6 +1740,22 @@
 		{6B29F634-1277-74B8-47F6-78756190BA7B}.Release-DLL|Win32.Build.0 = Release|Win32
 		{6B29F634-1277-74B8-47F6-78756190BA7B}.Release-DLL|x64.ActiveCfg = Release|x64
 		{6B29F634-1277-74B8-47F6-78756190BA7B}.Release-DLL|x64.Build.0 = Release|x64
+		{C237D1E4-8825-80BA-1FC3-5E147E53E96E}.Debug|Win32.ActiveCfg = Debug|Win32
+		{C237D1E4-8825-80BA-1FC3-5E147E53E96E}.Debug|x64.ActiveCfg = Debug|x64
+		{C237D1E4-8825-80BA-1FC3-5E147E53E96E}.Release|Win32.ActiveCfg = Release|Win32
+		{C237D1E4-8825-80BA-1FC3-5E147E53E96E}.Release|x64.ActiveCfg = Release|x64
+		{C237D1E4-8825-80BA-1FC3-5E147E53E96E}.Debug|Win32.Build.0 = Debug|Win32
+		{C237D1E4-8825-80BA-1FC3-5E147E53E96E}.Debug|x64.Build.0 = Debug|x64
+		{C237D1E4-8825-80BA-1FC3-5E147E53E96E}.Release|Win32.Build.0 = Release|Win32
+		{C237D1E4-8825-80BA-1FC3-5E147E53E96E}.Release|x64.Build.0 = Release|x64
+		{C237D1E4-8825-80BA-1FC3-5E147E53E96E}.Debug-DLL|Win32.ActiveCfg = Debug|Win32
+		{C237D1E4-8825-80BA-1FC3-5E147E53E96E}.Debug-DLL|Win32.Build.0 = Debug|Win32
+		{C237D1E4-8825-80BA-1FC3-5E147E53E96E}.Debug-DLL|x64.ActiveCfg = Debug|x64
+		{C237D1E4-8825-80BA-1FC3-5E147E53E96E}.Debug-DLL|x64.Build.0 = Debug|x64
+		{C237D1E4-8825-80BA-1FC3-5E147E53E96E}.Release-DLL|Win32.ActiveCfg = Release|Win32
+		{C237D1E4-8825-80BA-1FC3-5E147E53E96E}.Release-DLL|Win32.Build.0 = Release|Win32
+		{C237D1E4-8825-80BA-1FC3-5E147E53E96E}.Release-DLL|x64.ActiveCfg = Release|x64
+		{C237D1E4-8825-80BA-1FC3-5E147E53E96E}.Release-DLL|x64.Build.0 = Release|x64
 		{5AFE7D17-A4A7-D68E-4491-CBC852F9D2A0}.Debug|Win32.ActiveCfg = Debug|Win32
 		{5AFE7D17-A4A7-D68E-4491-CBC852F9D2A0}.Debug|x64.ActiveCfg = Debug|x64
 		{5AFE7D17-A4A7-D68E-4491-CBC852F9D2A0}.Release|Win32.ActiveCfg = Release|Win32
@@ -2072,6 +2108,22 @@
 		{38797EE3-62CC-3CBF-18D5-009ED6DD0BEC}.Release-DLL|Win32.Build.0 = Release|Win32
 		{38797EE3-62CC-3CBF-18D5-009ED6DD0BEC}.Release-DLL|x64.ActiveCfg = Release|x64
 		{38797EE3-62CC-3CBF-18D5-009ED6DD0BEC}.Release-DLL|x64.Build.0 = Release|x64
+		{B3D7760B-8BEA-2EF6-F1D4-9F9020E166D6}.Debug|Win32.ActiveCfg = Debug|Win32
+		{B3D7760B-8BEA-2EF6-F1D4-9F9020E166D6}.Debug|x64.ActiveCfg = Debug|x64
+		{B3D7760B-8BEA-2EF6-F1D4-9F9020E166D6}.Release|Win32.ActiveCfg = Release|Win32
+		{B3D7760B-8BEA-2EF6-F1D4-9F9020E166D6}.Release|x64.ActiveCfg = Release|x64
+		{B3D7760B-8BEA-2EF6-F1D4-9F9020E166D6}.Debug|Win32.Build.0 = Debug|Win32
+		{B3D7760B-8BEA-2EF6-F1D4-9F9020E166D6}.Debug|x64.Build.0 = Debug|x64
+		{B3D7760B-8BEA-2EF6-F1D4-9F9020E166D6}.Release|Win32.Build.0 = Release|Win32
+		{B3D7760B-8BEA-2EF6-F1D4-9F9020E166D6}.Release|x64.Build.0 = Release|x64
+		{B3D7760B-8BEA-2EF6-F1D4-9F9020E166D6}.Debug-DLL|Win32.ActiveCfg = Debug|Win32
+		{B3D7760B-8BEA-2EF6-F1D4-9F9020E166D6}.Debug-DLL|Win32.Build.0 = Debug|Win32
+		{B3D7760B-8BEA-2EF6-F1D4-9F9020E166D6}.Debug-DLL|x64.ActiveCfg = Debug|x64
+		{B3D7760B-8BEA-2EF6-F1D4-9F9020E166D6}.Debug-DLL|x64.Build.0 = Debug|x64
+		{B3D7760B-8BEA-2EF6-F1D4-9F9020E166D6}.Release-DLL|Win32.ActiveCfg = Release|Win32
+		{B3D7760B-8BEA-2EF6-F1D4-9F9020E166D6}.Release-DLL|Win32.Build.0 = Release|Win32
+		{B3D7760B-8BEA-2EF6-F1D4-9F9020E166D6}.Release-DLL|x64.ActiveCfg = Release|x64
+		{B3D7760B-8BEA-2EF6-F1D4-9F9020E166D6}.Release-DLL|x64.Build.0 = Release|x64
 		{8313AE17-FCFA-8110-95C7-7AF2F814D188}.Debug|Win32.ActiveCfg = Debug|Win32
 		{8313AE17-FCFA-8110-95C7-7AF2F814D188}.Debug|x64.ActiveCfg = Debug|x64
 		{8313AE17-FCFA-8110-95C7-7AF2F814D188}.Release|Win32.ActiveCfg = Release|Win32
diff --git a/vsprojects/vcxproj/gpr/gpr.vcxproj b/vsprojects/vcxproj/gpr/gpr.vcxproj
index a77c16d..60772c7 100644
--- a/vsprojects/vcxproj/gpr/gpr.vcxproj
+++ b/vsprojects/vcxproj/gpr/gpr.vcxproj
@@ -192,6 +192,7 @@
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\support\backoff.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\support\block_annotate.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\support\env.h" />
+    <ClInclude Include="$(SolutionDir)\..\src\core\lib\support\mpscq.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\support\murmur_hash.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\support\percent_encoding.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\support\stack_lockfree.h" />
@@ -242,6 +243,8 @@
     </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\src\core\lib\support\log_windows.c">
     </ClCompile>
+    <ClCompile Include="$(SolutionDir)\..\src\core\lib\support\mpscq.c">
+    </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\src\core\lib\support\murmur_hash.c">
     </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\src\core\lib\support\percent_encoding.c">
diff --git a/vsprojects/vcxproj/gpr/gpr.vcxproj.filters b/vsprojects/vcxproj/gpr/gpr.vcxproj.filters
index f6ba556..f2db937 100644
--- a/vsprojects/vcxproj/gpr/gpr.vcxproj.filters
+++ b/vsprojects/vcxproj/gpr/gpr.vcxproj.filters
@@ -61,6 +61,9 @@
     <ClCompile Include="$(SolutionDir)\..\src\core\lib\support\log_windows.c">
       <Filter>src\core\lib\support</Filter>
     </ClCompile>
+    <ClCompile Include="$(SolutionDir)\..\src\core\lib\support\mpscq.c">
+      <Filter>src\core\lib\support</Filter>
+    </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\src\core\lib\support\murmur_hash.c">
       <Filter>src\core\lib\support</Filter>
     </ClCompile>
@@ -272,6 +275,9 @@
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\support\env.h">
       <Filter>src\core\lib\support</Filter>
     </ClInclude>
+    <ClInclude Include="$(SolutionDir)\..\src\core\lib\support\mpscq.h">
+      <Filter>src\core\lib\support</Filter>
+    </ClInclude>
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\support\murmur_hash.h">
       <Filter>src\core\lib\support</Filter>
     </ClInclude>
diff --git a/vsprojects/vcxproj/grpc++/grpc++.vcxproj b/vsprojects/vcxproj/grpc++/grpc++.vcxproj
index cddc904..0a317da 100644
--- a/vsprojects/vcxproj/grpc++/grpc++.vcxproj
+++ b/vsprojects/vcxproj/grpc++/grpc++.vcxproj
@@ -352,6 +352,7 @@
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\service_type.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status_code_enum.h" />
+    <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status_helper.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\string_ref.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\stub_options.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\sync.h" />
@@ -385,6 +386,7 @@
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\http\httpcli.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\http\parser.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\closure.h" />
+    <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\combiner.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\endpoint.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\endpoint_pair.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\error.h" />
@@ -547,6 +549,8 @@
     </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\closure.c">
     </ClCompile>
+    <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\combiner.c">
+    </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\endpoint.c">
     </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\endpoint_pair_posix.c">
diff --git a/vsprojects/vcxproj/grpc++/grpc++.vcxproj.filters b/vsprojects/vcxproj/grpc++/grpc++.vcxproj.filters
index c9a4274..4bf4065 100644
--- a/vsprojects/vcxproj/grpc++/grpc++.vcxproj.filters
+++ b/vsprojects/vcxproj/grpc++/grpc++.vcxproj.filters
@@ -145,6 +145,9 @@
     <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\closure.c">
       <Filter>src\core\lib\iomgr</Filter>
     </ClCompile>
+    <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\combiner.c">
+      <Filter>src\core\lib\iomgr</Filter>
+    </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\endpoint.c">
       <Filter>src\core\lib\iomgr</Filter>
     </ClCompile>
@@ -654,6 +657,9 @@
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status_code_enum.h">
       <Filter>include\grpc++\impl\codegen</Filter>
     </ClInclude>
+    <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status_helper.h">
+      <Filter>include\grpc++\impl\codegen</Filter>
+    </ClInclude>
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\string_ref.h">
       <Filter>include\grpc++\impl\codegen</Filter>
     </ClInclude>
@@ -749,6 +755,9 @@
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\closure.h">
       <Filter>src\core\lib\iomgr</Filter>
     </ClInclude>
+    <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\combiner.h">
+      <Filter>src\core\lib\iomgr</Filter>
+    </ClInclude>
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\endpoint.h">
       <Filter>src\core\lib\iomgr</Filter>
     </ClInclude>
diff --git a/vsprojects/vcxproj/grpc++_reflection/grpc++_reflection.vcxproj b/vsprojects/vcxproj/grpc++_reflection/grpc++_reflection.vcxproj
index c073547..2301281 100644
--- a/vsprojects/vcxproj/grpc++_reflection/grpc++_reflection.vcxproj
+++ b/vsprojects/vcxproj/grpc++_reflection/grpc++_reflection.vcxproj
@@ -174,6 +174,7 @@
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\service_type.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status_code_enum.h" />
+    <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status_helper.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\string_ref.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\stub_options.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\sync.h" />
diff --git a/vsprojects/vcxproj/grpc++_reflection/grpc++_reflection.vcxproj.filters b/vsprojects/vcxproj/grpc++_reflection/grpc++_reflection.vcxproj.filters
index a7ae3fc..540e1c6 100644
--- a/vsprojects/vcxproj/grpc++_reflection/grpc++_reflection.vcxproj.filters
+++ b/vsprojects/vcxproj/grpc++_reflection/grpc++_reflection.vcxproj.filters
@@ -96,6 +96,9 @@
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status_code_enum.h">
       <Filter>include\grpc++\impl\codegen</Filter>
     </ClInclude>
+    <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status_helper.h">
+      <Filter>include\grpc++\impl\codegen</Filter>
+    </ClInclude>
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\string_ref.h">
       <Filter>include\grpc++\impl\codegen</Filter>
     </ClInclude>
diff --git a/vsprojects/vcxproj/grpc++_test_util/grpc++_test_util.vcxproj b/vsprojects/vcxproj/grpc++_test_util/grpc++_test_util.vcxproj
index c04f2f9..17e9199 100644
--- a/vsprojects/vcxproj/grpc++_test_util/grpc++_test_util.vcxproj
+++ b/vsprojects/vcxproj/grpc++_test_util/grpc++_test_util.vcxproj
@@ -170,6 +170,7 @@
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\service_type.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status_code_enum.h" />
+    <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status_helper.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\string_ref.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\stub_options.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\sync.h" />
diff --git a/vsprojects/vcxproj/grpc++_test_util/grpc++_test_util.vcxproj.filters b/vsprojects/vcxproj/grpc++_test_util/grpc++_test_util.vcxproj.filters
index 37ba3f0..25a1752 100644
--- a/vsprojects/vcxproj/grpc++_test_util/grpc++_test_util.vcxproj.filters
+++ b/vsprojects/vcxproj/grpc++_test_util/grpc++_test_util.vcxproj.filters
@@ -102,6 +102,9 @@
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status_code_enum.h">
       <Filter>include\grpc++\impl\codegen</Filter>
     </ClInclude>
+    <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status_helper.h">
+      <Filter>include\grpc++\impl\codegen</Filter>
+    </ClInclude>
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\string_ref.h">
       <Filter>include\grpc++\impl\codegen</Filter>
     </ClInclude>
diff --git a/vsprojects/vcxproj/grpc++_unsecure/grpc++_unsecure.vcxproj b/vsprojects/vcxproj/grpc++_unsecure/grpc++_unsecure.vcxproj
index 4146716..6b79f09 100644
--- a/vsprojects/vcxproj/grpc++_unsecure/grpc++_unsecure.vcxproj
+++ b/vsprojects/vcxproj/grpc++_unsecure/grpc++_unsecure.vcxproj
@@ -352,6 +352,7 @@
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\service_type.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status_code_enum.h" />
+    <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status_helper.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\string_ref.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\stub_options.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\sync.h" />
@@ -381,6 +382,7 @@
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\http\httpcli.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\http\parser.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\closure.h" />
+    <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\combiner.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\endpoint.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\endpoint_pair.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\error.h" />
@@ -533,6 +535,8 @@
     </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\closure.c">
     </ClCompile>
+    <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\combiner.c">
+    </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\endpoint.c">
     </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\endpoint_pair_posix.c">
diff --git a/vsprojects/vcxproj/grpc++_unsecure/grpc++_unsecure.vcxproj.filters b/vsprojects/vcxproj/grpc++_unsecure/grpc++_unsecure.vcxproj.filters
index 6746841..5c3a2df 100644
--- a/vsprojects/vcxproj/grpc++_unsecure/grpc++_unsecure.vcxproj.filters
+++ b/vsprojects/vcxproj/grpc++_unsecure/grpc++_unsecure.vcxproj.filters
@@ -130,6 +130,9 @@
     <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\closure.c">
       <Filter>src\core\lib\iomgr</Filter>
     </ClCompile>
+    <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\combiner.c">
+      <Filter>src\core\lib\iomgr</Filter>
+    </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\endpoint.c">
       <Filter>src\core\lib\iomgr</Filter>
     </ClCompile>
@@ -639,6 +642,9 @@
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status_code_enum.h">
       <Filter>include\grpc++\impl\codegen</Filter>
     </ClInclude>
+    <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status_helper.h">
+      <Filter>include\grpc++\impl\codegen</Filter>
+    </ClInclude>
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\string_ref.h">
       <Filter>include\grpc++\impl\codegen</Filter>
     </ClInclude>
@@ -722,6 +728,9 @@
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\closure.h">
       <Filter>src\core\lib\iomgr</Filter>
     </ClInclude>
+    <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\combiner.h">
+      <Filter>src\core\lib\iomgr</Filter>
+    </ClInclude>
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\endpoint.h">
       <Filter>src\core\lib\iomgr</Filter>
     </ClInclude>
diff --git a/vsprojects/vcxproj/grpc/grpc.vcxproj b/vsprojects/vcxproj/grpc/grpc.vcxproj
index badbffd..9ade6e3 100644
--- a/vsprojects/vcxproj/grpc/grpc.vcxproj
+++ b/vsprojects/vcxproj/grpc/grpc.vcxproj
@@ -311,6 +311,7 @@
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\http\httpcli.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\http\parser.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\closure.h" />
+    <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\combiner.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\endpoint.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\endpoint_pair.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\error.h" />
@@ -488,6 +489,8 @@
     </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\closure.c">
     </ClCompile>
+    <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\combiner.c">
+    </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\endpoint.c">
     </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\endpoint_pair_posix.c">
diff --git a/vsprojects/vcxproj/grpc/grpc.vcxproj.filters b/vsprojects/vcxproj/grpc/grpc.vcxproj.filters
index 19bdda4..2bc1bb0 100644
--- a/vsprojects/vcxproj/grpc/grpc.vcxproj.filters
+++ b/vsprojects/vcxproj/grpc/grpc.vcxproj.filters
@@ -49,6 +49,9 @@
     <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\closure.c">
       <Filter>src\core\lib\iomgr</Filter>
     </ClCompile>
+    <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\combiner.c">
+      <Filter>src\core\lib\iomgr</Filter>
+    </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\endpoint.c">
       <Filter>src\core\lib\iomgr</Filter>
     </ClCompile>
@@ -701,6 +704,9 @@
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\closure.h">
       <Filter>src\core\lib\iomgr</Filter>
     </ClInclude>
+    <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\combiner.h">
+      <Filter>src\core\lib\iomgr</Filter>
+    </ClInclude>
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\endpoint.h">
       <Filter>src\core\lib\iomgr</Filter>
     </ClInclude>
diff --git a/vsprojects/vcxproj/grpc_test_util/grpc_test_util.vcxproj b/vsprojects/vcxproj/grpc_test_util/grpc_test_util.vcxproj
index 8eaf7f6..d589009 100644
--- a/vsprojects/vcxproj/grpc_test_util/grpc_test_util.vcxproj
+++ b/vsprojects/vcxproj/grpc_test_util/grpc_test_util.vcxproj
@@ -202,6 +202,7 @@
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\http\httpcli.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\http\parser.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\closure.h" />
+    <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\combiner.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\endpoint.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\endpoint_pair.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\error.h" />
@@ -332,6 +333,8 @@
     </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\closure.c">
     </ClCompile>
+    <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\combiner.c">
+    </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\endpoint.c">
     </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\endpoint_pair_posix.c">
diff --git a/vsprojects/vcxproj/grpc_test_util/grpc_test_util.vcxproj.filters b/vsprojects/vcxproj/grpc_test_util/grpc_test_util.vcxproj.filters
index 2fc2c6d..e47b003 100644
--- a/vsprojects/vcxproj/grpc_test_util/grpc_test_util.vcxproj.filters
+++ b/vsprojects/vcxproj/grpc_test_util/grpc_test_util.vcxproj.filters
@@ -97,6 +97,9 @@
     <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\closure.c">
       <Filter>src\core\lib\iomgr</Filter>
     </ClCompile>
+    <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\combiner.c">
+      <Filter>src\core\lib\iomgr</Filter>
+    </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\endpoint.c">
       <Filter>src\core\lib\iomgr</Filter>
     </ClCompile>
@@ -482,6 +485,9 @@
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\closure.h">
       <Filter>src\core\lib\iomgr</Filter>
     </ClInclude>
+    <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\combiner.h">
+      <Filter>src\core\lib\iomgr</Filter>
+    </ClInclude>
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\endpoint.h">
       <Filter>src\core\lib\iomgr</Filter>
     </ClInclude>
diff --git a/vsprojects/vcxproj/grpc_unsecure/grpc_unsecure.vcxproj b/vsprojects/vcxproj/grpc_unsecure/grpc_unsecure.vcxproj
index 9d97645..13fca33 100644
--- a/vsprojects/vcxproj/grpc_unsecure/grpc_unsecure.vcxproj
+++ b/vsprojects/vcxproj/grpc_unsecure/grpc_unsecure.vcxproj
@@ -301,6 +301,7 @@
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\http\httpcli.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\http\parser.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\closure.h" />
+    <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\combiner.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\endpoint.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\endpoint_pair.h" />
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\error.h" />
@@ -456,6 +457,8 @@
     </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\closure.c">
     </ClCompile>
+    <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\combiner.c">
+    </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\endpoint.c">
     </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\endpoint_pair_posix.c">
diff --git a/vsprojects/vcxproj/grpc_unsecure/grpc_unsecure.vcxproj.filters b/vsprojects/vcxproj/grpc_unsecure/grpc_unsecure.vcxproj.filters
index 251a8fa..09007d4 100644
--- a/vsprojects/vcxproj/grpc_unsecure/grpc_unsecure.vcxproj.filters
+++ b/vsprojects/vcxproj/grpc_unsecure/grpc_unsecure.vcxproj.filters
@@ -52,6 +52,9 @@
     <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\closure.c">
       <Filter>src\core\lib\iomgr</Filter>
     </ClCompile>
+    <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\combiner.c">
+      <Filter>src\core\lib\iomgr</Filter>
+    </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\src\core\lib\iomgr\endpoint.c">
       <Filter>src\core\lib\iomgr</Filter>
     </ClCompile>
@@ -611,6 +614,9 @@
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\closure.h">
       <Filter>src\core\lib\iomgr</Filter>
     </ClInclude>
+    <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\combiner.h">
+      <Filter>src\core\lib\iomgr</Filter>
+    </ClInclude>
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\iomgr\endpoint.h">
       <Filter>src\core\lib\iomgr</Filter>
     </ClInclude>
diff --git a/vsprojects/vcxproj/test/codegen_test_full/codegen_test_full.vcxproj b/vsprojects/vcxproj/test/codegen_test_full/codegen_test_full.vcxproj
index 273c145..2d75735 100644
--- a/vsprojects/vcxproj/test/codegen_test_full/codegen_test_full.vcxproj
+++ b/vsprojects/vcxproj/test/codegen_test_full/codegen_test_full.vcxproj
@@ -183,6 +183,7 @@
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\service_type.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status_code_enum.h" />
+    <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status_helper.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\string_ref.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\stub_options.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\sync.h" />
diff --git a/vsprojects/vcxproj/test/codegen_test_full/codegen_test_full.vcxproj.filters b/vsprojects/vcxproj/test/codegen_test_full/codegen_test_full.vcxproj.filters
index e6d2dc2..dda7967 100644
--- a/vsprojects/vcxproj/test/codegen_test_full/codegen_test_full.vcxproj.filters
+++ b/vsprojects/vcxproj/test/codegen_test_full/codegen_test_full.vcxproj.filters
@@ -90,6 +90,9 @@
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status_code_enum.h">
       <Filter>include\grpc++\impl\codegen</Filter>
     </ClInclude>
+    <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status_helper.h">
+      <Filter>include\grpc++\impl\codegen</Filter>
+    </ClInclude>
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\string_ref.h">
       <Filter>include\grpc++\impl\codegen</Filter>
     </ClInclude>
diff --git a/vsprojects/vcxproj/test/codegen_test_minimal/codegen_test_minimal.vcxproj b/vsprojects/vcxproj/test/codegen_test_minimal/codegen_test_minimal.vcxproj
index b40d8c3..270c2a3 100644
--- a/vsprojects/vcxproj/test/codegen_test_minimal/codegen_test_minimal.vcxproj
+++ b/vsprojects/vcxproj/test/codegen_test_minimal/codegen_test_minimal.vcxproj
@@ -183,6 +183,7 @@
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\service_type.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status_code_enum.h" />
+    <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status_helper.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\string_ref.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\stub_options.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\sync.h" />
diff --git a/vsprojects/vcxproj/test/codegen_test_minimal/codegen_test_minimal.vcxproj.filters b/vsprojects/vcxproj/test/codegen_test_minimal/codegen_test_minimal.vcxproj.filters
index 6db6ab6..dc5e321 100644
--- a/vsprojects/vcxproj/test/codegen_test_minimal/codegen_test_minimal.vcxproj.filters
+++ b/vsprojects/vcxproj/test/codegen_test_minimal/codegen_test_minimal.vcxproj.filters
@@ -93,6 +93,9 @@
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status_code_enum.h">
       <Filter>include\grpc++\impl\codegen</Filter>
     </ClInclude>
+    <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status_helper.h">
+      <Filter>include\grpc++\impl\codegen</Filter>
+    </ClInclude>
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\string_ref.h">
       <Filter>include\grpc++\impl\codegen</Filter>
     </ClInclude>
diff --git a/vsprojects/vcxproj/test/combiner_test/combiner_test.vcxproj b/vsprojects/vcxproj/test/combiner_test/combiner_test.vcxproj
new file mode 100644
index 0000000..f889d21
--- /dev/null
+++ b/vsprojects/vcxproj/test/combiner_test/combiner_test.vcxproj
@@ -0,0 +1,199 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project DefaultTargets="Build" ToolsVersion="12.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <Import Project="$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.openssl.1.0.204.1\build\native\grpc.dependencies.openssl.props" Condition="Exists('$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.openssl.1.0.204.1\build\native\1.0.204.1.props')" />
+  <ItemGroup Label="ProjectConfigurations">
+    <ProjectConfiguration Include="Debug|Win32">
+      <Configuration>Debug</Configuration>
+      <Platform>Win32</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="Debug|x64">
+      <Configuration>Debug</Configuration>
+      <Platform>x64</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="Release|Win32">
+      <Configuration>Release</Configuration>
+      <Platform>Win32</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="Release|x64">
+      <Configuration>Release</Configuration>
+      <Platform>x64</Platform>
+    </ProjectConfiguration>
+  </ItemGroup>
+  <PropertyGroup Label="Globals">
+    <ProjectGuid>{C237D1E4-8825-80BA-1FC3-5E147E53E96E}</ProjectGuid>
+    <IgnoreWarnIntDirInTempDetected>true</IgnoreWarnIntDirInTempDetected>
+    <IntDir>$(SolutionDir)IntDir\$(MSBuildProjectName)\</IntDir>
+  </PropertyGroup>
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.Default.props" />
+  <PropertyGroup Condition="'$(VisualStudioVersion)' == '10.0'" Label="Configuration">
+    <PlatformToolset>v100</PlatformToolset>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(VisualStudioVersion)' == '11.0'" Label="Configuration">
+    <PlatformToolset>v110</PlatformToolset>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(VisualStudioVersion)' == '12.0'" Label="Configuration">
+    <PlatformToolset>v120</PlatformToolset>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(VisualStudioVersion)' == '14.0'" Label="Configuration">
+    <PlatformToolset>v140</PlatformToolset>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)'=='Debug'" Label="Configuration">
+    <ConfigurationType>Application</ConfigurationType>
+    <UseDebugLibraries>true</UseDebugLibraries>
+    <CharacterSet>Unicode</CharacterSet>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)'=='Release'" Label="Configuration">
+    <ConfigurationType>Application</ConfigurationType>
+    <UseDebugLibraries>false</UseDebugLibraries>
+    <WholeProgramOptimization>true</WholeProgramOptimization>
+    <CharacterSet>Unicode</CharacterSet>
+  </PropertyGroup>
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.props" />
+  <ImportGroup Label="ExtensionSettings">
+  </ImportGroup>
+  <ImportGroup Label="PropertySheets">
+    <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
+    <Import Project="$(SolutionDir)\..\vsprojects\global.props" />
+    <Import Project="$(SolutionDir)\..\vsprojects\openssl.props" />
+    <Import Project="$(SolutionDir)\..\vsprojects\winsock.props" />
+    <Import Project="$(SolutionDir)\..\vsprojects\zlib.props" />
+  </ImportGroup>
+  <PropertyGroup Label="UserMacros" />
+  <PropertyGroup Condition="'$(Configuration)'=='Debug'">
+    <TargetName>combiner_test</TargetName>
+    <Linkage-grpc_dependencies_zlib>static</Linkage-grpc_dependencies_zlib>
+    <Configuration-grpc_dependencies_zlib>Debug</Configuration-grpc_dependencies_zlib>
+    <Linkage-grpc_dependencies_openssl>static</Linkage-grpc_dependencies_openssl>
+    <Configuration-grpc_dependencies_openssl>Debug</Configuration-grpc_dependencies_openssl>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)'=='Release'">
+    <TargetName>combiner_test</TargetName>
+    <Linkage-grpc_dependencies_zlib>static</Linkage-grpc_dependencies_zlib>
+    <Configuration-grpc_dependencies_zlib>Release</Configuration-grpc_dependencies_zlib>
+    <Linkage-grpc_dependencies_openssl>static</Linkage-grpc_dependencies_openssl>
+    <Configuration-grpc_dependencies_openssl>Release</Configuration-grpc_dependencies_openssl>
+  </PropertyGroup>
+    <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">
+    <ClCompile>
+      <PrecompiledHeader>NotUsing</PrecompiledHeader>
+      <WarningLevel>Level3</WarningLevel>
+      <Optimization>Disabled</Optimization>
+      <PreprocessorDefinitions>WIN32;_DEBUG;_LIB;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <SDLCheck>true</SDLCheck>
+      <RuntimeLibrary>MultiThreadedDebug</RuntimeLibrary>
+      <TreatWarningAsError>true</TreatWarningAsError>
+      <DebugInformationFormat Condition="$(Jenkins)">None</DebugInformationFormat>
+      <MinimalRebuild Condition="$(Jenkins)">false</MinimalRebuild>
+    </ClCompile>
+    <Link>
+      <SubSystem>Console</SubSystem>
+      <GenerateDebugInformation Condition="!$(Jenkins)">true</GenerateDebugInformation>
+      <GenerateDebugInformation Condition="$(Jenkins)">false</GenerateDebugInformation>
+    </Link>
+  </ItemDefinitionGroup>
+
+    <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Debug|x64'">
+    <ClCompile>
+      <PrecompiledHeader>NotUsing</PrecompiledHeader>
+      <WarningLevel>Level3</WarningLevel>
+      <Optimization>Disabled</Optimization>
+      <PreprocessorDefinitions>WIN32;_DEBUG;_LIB;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <SDLCheck>true</SDLCheck>
+      <RuntimeLibrary>MultiThreadedDebug</RuntimeLibrary>
+      <TreatWarningAsError>true</TreatWarningAsError>
+      <DebugInformationFormat Condition="$(Jenkins)">None</DebugInformationFormat>
+      <MinimalRebuild Condition="$(Jenkins)">false</MinimalRebuild>
+    </ClCompile>
+    <Link>
+      <SubSystem>Console</SubSystem>
+      <GenerateDebugInformation Condition="!$(Jenkins)">true</GenerateDebugInformation>
+      <GenerateDebugInformation Condition="$(Jenkins)">false</GenerateDebugInformation>
+    </Link>
+  </ItemDefinitionGroup>
+
+    <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">
+    <ClCompile>
+      <PrecompiledHeader>NotUsing</PrecompiledHeader>
+      <WarningLevel>Level3</WarningLevel>
+      <Optimization>MaxSpeed</Optimization>
+      <PreprocessorDefinitions>WIN32;NDEBUG;_LIB;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <FunctionLevelLinking>true</FunctionLevelLinking>
+      <IntrinsicFunctions>true</IntrinsicFunctions>
+      <SDLCheck>true</SDLCheck>
+      <RuntimeLibrary>MultiThreaded</RuntimeLibrary>
+      <TreatWarningAsError>true</TreatWarningAsError>
+      <DebugInformationFormat Condition="$(Jenkins)">None</DebugInformationFormat>
+      <MinimalRebuild Condition="$(Jenkins)">false</MinimalRebuild>
+    </ClCompile>
+    <Link>
+      <SubSystem>Console</SubSystem>
+      <GenerateDebugInformation Condition="!$(Jenkins)">true</GenerateDebugInformation>
+      <GenerateDebugInformation Condition="$(Jenkins)">false</GenerateDebugInformation>
+      <EnableCOMDATFolding>true</EnableCOMDATFolding>
+      <OptimizeReferences>true</OptimizeReferences>
+    </Link>
+  </ItemDefinitionGroup>
+
+    <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Release|x64'">
+    <ClCompile>
+      <PrecompiledHeader>NotUsing</PrecompiledHeader>
+      <WarningLevel>Level3</WarningLevel>
+      <Optimization>MaxSpeed</Optimization>
+      <PreprocessorDefinitions>WIN32;NDEBUG;_LIB;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <FunctionLevelLinking>true</FunctionLevelLinking>
+      <IntrinsicFunctions>true</IntrinsicFunctions>
+      <SDLCheck>true</SDLCheck>
+      <RuntimeLibrary>MultiThreaded</RuntimeLibrary>
+      <TreatWarningAsError>true</TreatWarningAsError>
+      <DebugInformationFormat Condition="$(Jenkins)">None</DebugInformationFormat>
+      <MinimalRebuild Condition="$(Jenkins)">false</MinimalRebuild>
+    </ClCompile>
+    <Link>
+      <SubSystem>Console</SubSystem>
+      <GenerateDebugInformation Condition="!$(Jenkins)">true</GenerateDebugInformation>
+      <GenerateDebugInformation Condition="$(Jenkins)">false</GenerateDebugInformation>
+      <EnableCOMDATFolding>true</EnableCOMDATFolding>
+      <OptimizeReferences>true</OptimizeReferences>
+    </Link>
+  </ItemDefinitionGroup>
+
+  <ItemGroup>
+    <ClCompile Include="$(SolutionDir)\..\test\core\iomgr\combiner_test.c">
+    </ClCompile>
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(SolutionDir)\..\vsprojects\vcxproj\.\grpc_test_util\grpc_test_util.vcxproj">
+      <Project>{17BCAFC0-5FDC-4C94-AEB9-95F3E220614B}</Project>
+    </ProjectReference>
+    <ProjectReference Include="$(SolutionDir)\..\vsprojects\vcxproj\.\grpc\grpc.vcxproj">
+      <Project>{29D16885-7228-4C31-81ED-5F9187C7F2A9}</Project>
+    </ProjectReference>
+    <ProjectReference Include="$(SolutionDir)\..\vsprojects\vcxproj\.\gpr_test_util\gpr_test_util.vcxproj">
+      <Project>{EAB0A629-17A9-44DB-B5FF-E91A721FE037}</Project>
+    </ProjectReference>
+    <ProjectReference Include="$(SolutionDir)\..\vsprojects\vcxproj\.\gpr\gpr.vcxproj">
+      <Project>{B23D3D1A-9438-4EDA-BEB6-9A0A03D17792}</Project>
+    </ProjectReference>
+  </ItemGroup>
+  <ItemGroup>
+    <None Include="packages.config" />
+  </ItemGroup>
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
+  <ImportGroup Label="ExtensionTargets">
+  <Import Project="$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.zlib.redist.1.2.8.10\build\native\grpc.dependencies.zlib.redist.targets" Condition="Exists('$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.zlib.redist.1.2.8.10\build\native\grpc.dependencies\grpc.dependencies.zlib.targets')" />
+  <Import Project="$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.zlib.1.2.8.10\build\native\grpc.dependencies.zlib.targets" Condition="Exists('$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.zlib.1.2.8.10\build\native\grpc.dependencies\grpc.dependencies.zlib.targets')" />
+  <Import Project="$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.openssl.redist.1.0.204.1\build\native\grpc.dependencies.openssl.redist.targets" Condition="Exists('$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.openssl.redist.1.0.204.1\build\native\grpc.dependencies\grpc.dependencies.openssl.targets')" />
+  <Import Project="$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.openssl.1.0.204.1\build\native\grpc.dependencies.openssl.targets" Condition="Exists('$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.openssl.1.0.204.1\build\native\grpc.dependencies\grpc.dependencies.openssl.targets')" />
+  </ImportGroup>
+  <Target Name="EnsureNuGetPackageBuildImports" BeforeTargets="PrepareForBuild">
+    <PropertyGroup>
+      <ErrorText>This project references NuGet package(s) that are missing on this computer. Enable NuGet Package Restore to download them.  For more information, see http://go.microsoft.com/fwlink/?LinkID=322105. The missing file is {0}.</ErrorText>
+    </PropertyGroup>
+    <Error Condition="!Exists('$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.zlib.redist.1.2.8.10\build\native\grpc.dependencies.zlib.redist.targets')" Text="$([System.String]::Format('$(ErrorText)', '$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.zlib.redist.1.2.8.10\build\native\grpc.dependencies.zlib.redist.targets')" />
+    <Error Condition="!Exists('$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.zlib.1.2.8.10\build\native\grpc.dependencies.zlib.targets')" Text="$([System.String]::Format('$(ErrorText)', '$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.zlib.1.2.8.10\build\native\grpc.dependencies.zlib.targets')" />
+    <Error Condition="!Exists('$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.openssl.redist.1.0.204.1\build\native\grpc.dependencies.openssl.redist.targets')" Text="$([System.String]::Format('$(ErrorText)', '$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.openssl.redist.1.0.204.1\build\native\grpc.dependencies.openssl.redist.targets')" />
+    <Error Condition="!Exists('$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.openssl.1.0.204.1\build\native\grpc.dependencies.openssl.props')" Text="$([System.String]::Format('$(ErrorText)', '$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.openssl.1.0.204.1\build\native\grpc.dependencies.openssl.props')" />
+    <Error Condition="!Exists('$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.openssl.1.0.204.1\build\native\grpc.dependencies.openssl.targets')" Text="$([System.String]::Format('$(ErrorText)', '$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.openssl.1.0.204.1\build\native\grpc.dependencies.openssl.targets')" />
+  </Target>
+</Project>
+
diff --git a/vsprojects/vcxproj/test/combiner_test/combiner_test.vcxproj.filters b/vsprojects/vcxproj/test/combiner_test/combiner_test.vcxproj.filters
new file mode 100644
index 0000000..e8ebb09
--- /dev/null
+++ b/vsprojects/vcxproj/test/combiner_test/combiner_test.vcxproj.filters
@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <ItemGroup>
+    <ClCompile Include="$(SolutionDir)\..\test\core\iomgr\combiner_test.c">
+      <Filter>test\core\iomgr</Filter>
+    </ClCompile>
+  </ItemGroup>
+
+  <ItemGroup>
+    <Filter Include="test">
+      <UniqueIdentifier>{82bca2af-d499-b405-fd05-4d345372496c}</UniqueIdentifier>
+    </Filter>
+    <Filter Include="test\core">
+      <UniqueIdentifier>{c32d8e20-b719-532d-ba23-bd9d523fac15}</UniqueIdentifier>
+    </Filter>
+    <Filter Include="test\core\iomgr">
+      <UniqueIdentifier>{b4fa8ca1-e6c7-dec5-6d62-8a62396825c6}</UniqueIdentifier>
+    </Filter>
+  </ItemGroup>
+</Project>
+
diff --git a/vsprojects/vcxproj/test/gpr_mpscq_test/gpr_mpscq_test.vcxproj b/vsprojects/vcxproj/test/gpr_mpscq_test/gpr_mpscq_test.vcxproj
new file mode 100644
index 0000000..0134286
--- /dev/null
+++ b/vsprojects/vcxproj/test/gpr_mpscq_test/gpr_mpscq_test.vcxproj
@@ -0,0 +1,193 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project DefaultTargets="Build" ToolsVersion="12.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <Import Project="$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.openssl.1.0.204.1\build\native\grpc.dependencies.openssl.props" Condition="Exists('$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.openssl.1.0.204.1\build\native\1.0.204.1.props')" />
+  <ItemGroup Label="ProjectConfigurations">
+    <ProjectConfiguration Include="Debug|Win32">
+      <Configuration>Debug</Configuration>
+      <Platform>Win32</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="Debug|x64">
+      <Configuration>Debug</Configuration>
+      <Platform>x64</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="Release|Win32">
+      <Configuration>Release</Configuration>
+      <Platform>Win32</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="Release|x64">
+      <Configuration>Release</Configuration>
+      <Platform>x64</Platform>
+    </ProjectConfiguration>
+  </ItemGroup>
+  <PropertyGroup Label="Globals">
+    <ProjectGuid>{B3D7760B-8BEA-2EF6-F1D4-9F9020E166D6}</ProjectGuid>
+    <IgnoreWarnIntDirInTempDetected>true</IgnoreWarnIntDirInTempDetected>
+    <IntDir>$(SolutionDir)IntDir\$(MSBuildProjectName)\</IntDir>
+  </PropertyGroup>
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.Default.props" />
+  <PropertyGroup Condition="'$(VisualStudioVersion)' == '10.0'" Label="Configuration">
+    <PlatformToolset>v100</PlatformToolset>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(VisualStudioVersion)' == '11.0'" Label="Configuration">
+    <PlatformToolset>v110</PlatformToolset>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(VisualStudioVersion)' == '12.0'" Label="Configuration">
+    <PlatformToolset>v120</PlatformToolset>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(VisualStudioVersion)' == '14.0'" Label="Configuration">
+    <PlatformToolset>v140</PlatformToolset>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)'=='Debug'" Label="Configuration">
+    <ConfigurationType>Application</ConfigurationType>
+    <UseDebugLibraries>true</UseDebugLibraries>
+    <CharacterSet>Unicode</CharacterSet>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)'=='Release'" Label="Configuration">
+    <ConfigurationType>Application</ConfigurationType>
+    <UseDebugLibraries>false</UseDebugLibraries>
+    <WholeProgramOptimization>true</WholeProgramOptimization>
+    <CharacterSet>Unicode</CharacterSet>
+  </PropertyGroup>
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.props" />
+  <ImportGroup Label="ExtensionSettings">
+  </ImportGroup>
+  <ImportGroup Label="PropertySheets">
+    <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
+    <Import Project="$(SolutionDir)\..\vsprojects\global.props" />
+    <Import Project="$(SolutionDir)\..\vsprojects\openssl.props" />
+    <Import Project="$(SolutionDir)\..\vsprojects\winsock.props" />
+    <Import Project="$(SolutionDir)\..\vsprojects\zlib.props" />
+  </ImportGroup>
+  <PropertyGroup Label="UserMacros" />
+  <PropertyGroup Condition="'$(Configuration)'=='Debug'">
+    <TargetName>gpr_mpscq_test</TargetName>
+    <Linkage-grpc_dependencies_zlib>static</Linkage-grpc_dependencies_zlib>
+    <Configuration-grpc_dependencies_zlib>Debug</Configuration-grpc_dependencies_zlib>
+    <Linkage-grpc_dependencies_openssl>static</Linkage-grpc_dependencies_openssl>
+    <Configuration-grpc_dependencies_openssl>Debug</Configuration-grpc_dependencies_openssl>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)'=='Release'">
+    <TargetName>gpr_mpscq_test</TargetName>
+    <Linkage-grpc_dependencies_zlib>static</Linkage-grpc_dependencies_zlib>
+    <Configuration-grpc_dependencies_zlib>Release</Configuration-grpc_dependencies_zlib>
+    <Linkage-grpc_dependencies_openssl>static</Linkage-grpc_dependencies_openssl>
+    <Configuration-grpc_dependencies_openssl>Release</Configuration-grpc_dependencies_openssl>
+  </PropertyGroup>
+    <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">
+    <ClCompile>
+      <PrecompiledHeader>NotUsing</PrecompiledHeader>
+      <WarningLevel>Level3</WarningLevel>
+      <Optimization>Disabled</Optimization>
+      <PreprocessorDefinitions>WIN32;_DEBUG;_LIB;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <SDLCheck>true</SDLCheck>
+      <RuntimeLibrary>MultiThreadedDebug</RuntimeLibrary>
+      <TreatWarningAsError>true</TreatWarningAsError>
+      <DebugInformationFormat Condition="$(Jenkins)">None</DebugInformationFormat>
+      <MinimalRebuild Condition="$(Jenkins)">false</MinimalRebuild>
+    </ClCompile>
+    <Link>
+      <SubSystem>Console</SubSystem>
+      <GenerateDebugInformation Condition="!$(Jenkins)">true</GenerateDebugInformation>
+      <GenerateDebugInformation Condition="$(Jenkins)">false</GenerateDebugInformation>
+    </Link>
+  </ItemDefinitionGroup>
+
+    <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Debug|x64'">
+    <ClCompile>
+      <PrecompiledHeader>NotUsing</PrecompiledHeader>
+      <WarningLevel>Level3</WarningLevel>
+      <Optimization>Disabled</Optimization>
+      <PreprocessorDefinitions>WIN32;_DEBUG;_LIB;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <SDLCheck>true</SDLCheck>
+      <RuntimeLibrary>MultiThreadedDebug</RuntimeLibrary>
+      <TreatWarningAsError>true</TreatWarningAsError>
+      <DebugInformationFormat Condition="$(Jenkins)">None</DebugInformationFormat>
+      <MinimalRebuild Condition="$(Jenkins)">false</MinimalRebuild>
+    </ClCompile>
+    <Link>
+      <SubSystem>Console</SubSystem>
+      <GenerateDebugInformation Condition="!$(Jenkins)">true</GenerateDebugInformation>
+      <GenerateDebugInformation Condition="$(Jenkins)">false</GenerateDebugInformation>
+    </Link>
+  </ItemDefinitionGroup>
+
+    <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">
+    <ClCompile>
+      <PrecompiledHeader>NotUsing</PrecompiledHeader>
+      <WarningLevel>Level3</WarningLevel>
+      <Optimization>MaxSpeed</Optimization>
+      <PreprocessorDefinitions>WIN32;NDEBUG;_LIB;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <FunctionLevelLinking>true</FunctionLevelLinking>
+      <IntrinsicFunctions>true</IntrinsicFunctions>
+      <SDLCheck>true</SDLCheck>
+      <RuntimeLibrary>MultiThreaded</RuntimeLibrary>
+      <TreatWarningAsError>true</TreatWarningAsError>
+      <DebugInformationFormat Condition="$(Jenkins)">None</DebugInformationFormat>
+      <MinimalRebuild Condition="$(Jenkins)">false</MinimalRebuild>
+    </ClCompile>
+    <Link>
+      <SubSystem>Console</SubSystem>
+      <GenerateDebugInformation Condition="!$(Jenkins)">true</GenerateDebugInformation>
+      <GenerateDebugInformation Condition="$(Jenkins)">false</GenerateDebugInformation>
+      <EnableCOMDATFolding>true</EnableCOMDATFolding>
+      <OptimizeReferences>true</OptimizeReferences>
+    </Link>
+  </ItemDefinitionGroup>
+
+    <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Release|x64'">
+    <ClCompile>
+      <PrecompiledHeader>NotUsing</PrecompiledHeader>
+      <WarningLevel>Level3</WarningLevel>
+      <Optimization>MaxSpeed</Optimization>
+      <PreprocessorDefinitions>WIN32;NDEBUG;_LIB;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <FunctionLevelLinking>true</FunctionLevelLinking>
+      <IntrinsicFunctions>true</IntrinsicFunctions>
+      <SDLCheck>true</SDLCheck>
+      <RuntimeLibrary>MultiThreaded</RuntimeLibrary>
+      <TreatWarningAsError>true</TreatWarningAsError>
+      <DebugInformationFormat Condition="$(Jenkins)">None</DebugInformationFormat>
+      <MinimalRebuild Condition="$(Jenkins)">false</MinimalRebuild>
+    </ClCompile>
+    <Link>
+      <SubSystem>Console</SubSystem>
+      <GenerateDebugInformation Condition="!$(Jenkins)">true</GenerateDebugInformation>
+      <GenerateDebugInformation Condition="$(Jenkins)">false</GenerateDebugInformation>
+      <EnableCOMDATFolding>true</EnableCOMDATFolding>
+      <OptimizeReferences>true</OptimizeReferences>
+    </Link>
+  </ItemDefinitionGroup>
+
+  <ItemGroup>
+    <ClCompile Include="$(SolutionDir)\..\test\core\support\mpscq_test.c">
+    </ClCompile>
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="$(SolutionDir)\..\vsprojects\vcxproj\.\gpr_test_util\gpr_test_util.vcxproj">
+      <Project>{EAB0A629-17A9-44DB-B5FF-E91A721FE037}</Project>
+    </ProjectReference>
+    <ProjectReference Include="$(SolutionDir)\..\vsprojects\vcxproj\.\gpr\gpr.vcxproj">
+      <Project>{B23D3D1A-9438-4EDA-BEB6-9A0A03D17792}</Project>
+    </ProjectReference>
+  </ItemGroup>
+  <ItemGroup>
+    <None Include="packages.config" />
+  </ItemGroup>
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
+  <ImportGroup Label="ExtensionTargets">
+  <Import Project="$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.zlib.redist.1.2.8.10\build\native\grpc.dependencies.zlib.redist.targets" Condition="Exists('$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.zlib.redist.1.2.8.10\build\native\grpc.dependencies\grpc.dependencies.zlib.targets')" />
+  <Import Project="$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.zlib.1.2.8.10\build\native\grpc.dependencies.zlib.targets" Condition="Exists('$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.zlib.1.2.8.10\build\native\grpc.dependencies\grpc.dependencies.zlib.targets')" />
+  <Import Project="$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.openssl.redist.1.0.204.1\build\native\grpc.dependencies.openssl.redist.targets" Condition="Exists('$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.openssl.redist.1.0.204.1\build\native\grpc.dependencies\grpc.dependencies.openssl.targets')" />
+  <Import Project="$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.openssl.1.0.204.1\build\native\grpc.dependencies.openssl.targets" Condition="Exists('$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.openssl.1.0.204.1\build\native\grpc.dependencies\grpc.dependencies.openssl.targets')" />
+  </ImportGroup>
+  <Target Name="EnsureNuGetPackageBuildImports" BeforeTargets="PrepareForBuild">
+    <PropertyGroup>
+      <ErrorText>This project references NuGet package(s) that are missing on this computer. Enable NuGet Package Restore to download them.  For more information, see http://go.microsoft.com/fwlink/?LinkID=322105. The missing file is {0}.</ErrorText>
+    </PropertyGroup>
+    <Error Condition="!Exists('$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.zlib.redist.1.2.8.10\build\native\grpc.dependencies.zlib.redist.targets')" Text="$([System.String]::Format('$(ErrorText)', '$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.zlib.redist.1.2.8.10\build\native\grpc.dependencies.zlib.redist.targets')" />
+    <Error Condition="!Exists('$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.zlib.1.2.8.10\build\native\grpc.dependencies.zlib.targets')" Text="$([System.String]::Format('$(ErrorText)', '$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.zlib.1.2.8.10\build\native\grpc.dependencies.zlib.targets')" />
+    <Error Condition="!Exists('$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.openssl.redist.1.0.204.1\build\native\grpc.dependencies.openssl.redist.targets')" Text="$([System.String]::Format('$(ErrorText)', '$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.openssl.redist.1.0.204.1\build\native\grpc.dependencies.openssl.redist.targets')" />
+    <Error Condition="!Exists('$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.openssl.1.0.204.1\build\native\grpc.dependencies.openssl.props')" Text="$([System.String]::Format('$(ErrorText)', '$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.openssl.1.0.204.1\build\native\grpc.dependencies.openssl.props')" />
+    <Error Condition="!Exists('$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.openssl.1.0.204.1\build\native\grpc.dependencies.openssl.targets')" Text="$([System.String]::Format('$(ErrorText)', '$(SolutionDir)\..\vsprojects\packages\grpc.dependencies.openssl.1.0.204.1\build\native\grpc.dependencies.openssl.targets')" />
+  </Target>
+</Project>
+
diff --git a/vsprojects/vcxproj/test/gpr_mpscq_test/gpr_mpscq_test.vcxproj.filters b/vsprojects/vcxproj/test/gpr_mpscq_test/gpr_mpscq_test.vcxproj.filters
new file mode 100644
index 0000000..9cceb9f
--- /dev/null
+++ b/vsprojects/vcxproj/test/gpr_mpscq_test/gpr_mpscq_test.vcxproj.filters
@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <ItemGroup>
+    <ClCompile Include="$(SolutionDir)\..\test\core\support\mpscq_test.c">
+      <Filter>test\core\support</Filter>
+    </ClCompile>
+  </ItemGroup>
+
+  <ItemGroup>
+    <Filter Include="test">
+      <UniqueIdentifier>{e82fb80c-10ba-2959-55d6-8653715f1e4f}</UniqueIdentifier>
+    </Filter>
+    <Filter Include="test\core">
+      <UniqueIdentifier>{32120233-25e6-f3e4-f828-c6408d47ec04}</UniqueIdentifier>
+    </Filter>
+    <Filter Include="test\core\support">
+      <UniqueIdentifier>{aa3a22bc-229a-c00a-dd4a-924c818c6a49}</UniqueIdentifier>
+    </Filter>
+  </ItemGroup>
+</Project>
+
diff --git a/vsprojects/vcxproj/test/grpc_tool_test/grpc_tool_test.vcxproj b/vsprojects/vcxproj/test/grpc_tool_test/grpc_tool_test.vcxproj
index 76f4415..bdf310d 100644
--- a/vsprojects/vcxproj/test/grpc_tool_test/grpc_tool_test.vcxproj
+++ b/vsprojects/vcxproj/test/grpc_tool_test/grpc_tool_test.vcxproj
@@ -184,6 +184,7 @@
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\service_type.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status_code_enum.h" />
+    <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status_helper.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\string_ref.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\stub_options.h" />
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\sync.h" />
diff --git a/vsprojects/vcxproj/test/grpc_tool_test/grpc_tool_test.vcxproj.filters b/vsprojects/vcxproj/test/grpc_tool_test/grpc_tool_test.vcxproj.filters
index 7839050..cd341e9 100644
--- a/vsprojects/vcxproj/test/grpc_tool_test/grpc_tool_test.vcxproj.filters
+++ b/vsprojects/vcxproj/test/grpc_tool_test/grpc_tool_test.vcxproj.filters
@@ -87,6 +87,9 @@
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status_code_enum.h">
       <Filter>include\grpc++\impl\codegen</Filter>
     </ClInclude>
+    <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\status_helper.h">
+      <Filter>include\grpc++\impl\codegen</Filter>
+    </ClInclude>
     <ClInclude Include="$(SolutionDir)\..\include\grpc++\impl\codegen\string_ref.h">
       <Filter>include\grpc++\impl\codegen</Filter>
     </ClInclude>