generalize build_artifacts.py
diff --git a/tools/run_tests/task_runner.py b/tools/run_tests/task_runner.py
new file mode 100644
index 0000000..39b15cc
--- /dev/null
+++ b/tools/run_tests/task_runner.py
@@ -0,0 +1,124 @@
+#!/usr/bin/env python
+# 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.
+
+"""Runs selected gRPC test/build tasks."""
+
+import argparse
+import atexit
+import jobset
+import multiprocessing
+import sys
+
+import artifact_targets
+import package_targets
+
+_TARGETS = []
+_TARGETS += artifact_targets.targets()
+_TARGETS += package_targets.targets()
+
+def _create_build_map():
+  """Maps task names and labels to list of tasks to be built."""
+  target_build_map = dict([(target.name, [target])
+                           for target in _TARGETS])
+  if len(_TARGETS) > len(target_build_map.keys()):
+    raise Exception('Target names need to be unique')
+
+  label_build_map = {}
+  label_build_map['all'] = [t for t in _TARGETS]  # to build all targets
+  for target in _TARGETS:
+    for label in target.labels:
+      if label in label_build_map:
+        label_build_map[label].append(target)
+      else:
+        label_build_map[label] = [target]
+
+  if set(target_build_map.keys()).intersection(label_build_map.keys()):
+    raise Exception('Target names need to be distinct from label names')
+  return dict( target_build_map.items() + label_build_map.items())
+
+
+_BUILD_MAP = _create_build_map()
+
+argp = argparse.ArgumentParser(description='Runs build/test targets.')
+argp.add_argument('-b', '--build',
+                  choices=sorted(_BUILD_MAP.keys()),
+                  nargs='+',
+                  default=['all'],
+                  help='Target name or target label to build.')
+argp.add_argument('-f', '--filter',
+                  choices=sorted(_BUILD_MAP.keys()),
+                  nargs='+',
+                  default=[],
+                  help='Filter targets to build with AND semantics.')
+argp.add_argument('-j', '--jobs', default=multiprocessing.cpu_count(), type=int)
+argp.add_argument('-t', '--travis',
+                  default=False,
+                  action='store_const',
+                  const=True)
+
+args = argp.parse_args()
+
+# Figure out which targets to build
+targets = []
+for label in args.build:
+  targets += _BUILD_MAP[label]
+
+# Among targets selected by -b, filter out those that don't match the filter
+targets = [t for t in targets if all(f in t.labels for f in args.filter)]
+targets = sorted(set(targets))
+
+# Execute pre-build phase
+prebuild_jobs = []
+for target in targets:
+  prebuild_jobs += target.pre_build_jobspecs()
+if prebuild_jobs:
+  num_failures, _ = jobset.run(
+    prebuild_jobs, newline_on_success=True, maxjobs=args.jobs)
+  if num_failures != 0:
+    jobset.message('FAILED', 'Pre-build phase failed.', do_newline=True)
+    sys.exit(1)
+
+build_jobs = []
+for target in targets:
+  build_jobs.append(target.build_jobspec())
+if not build_jobs:
+  print 'Nothing to build.'
+  sys.exit(1)
+
+jobset.message('START', 'Building targets.', do_newline=True)
+num_failures, _ = jobset.run(
+    build_jobs, newline_on_success=True, maxjobs=args.jobs)
+if num_failures == 0:
+  jobset.message('SUCCESS', 'All targets built successfully.',
+                 do_newline=True)
+else:
+  jobset.message('FAILED', 'Failed to build targets.',
+                 do_newline=True)
+  sys.exit(1)