diff --git a/Lib/test/libregrtest/main.py b/Lib/test/libregrtest/main.py
index 02717d8c..a9b2b35 100644
--- a/Lib/test/libregrtest/main.py
+++ b/Lib/test/libregrtest/main.py
@@ -1,6 +1,5 @@
 import datetime
 import faulthandler
-import json
 import locale
 import os
 import platform
@@ -22,22 +21,6 @@
 from test import support
 
 
-# When tests are run from the Python build directory, it is best practice
-# to keep the test files in a subfolder.  This eases the cleanup of leftover
-# files using the "make distclean" command.
-if sysconfig.is_python_build():
-    TEMPDIR = sysconfig.get_config_var('abs_builddir')
-    if TEMPDIR is None:
-        # bpo-30284: On Windows, only srcdir is available. Using abs_builddir
-        # mostly matters on UNIX when building Python out of the source tree,
-        # especially when the source tree is read only.
-        TEMPDIR = sysconfig.get_config_var('srcdir')
-    TEMPDIR = os.path.join(TEMPDIR, 'build')
-else:
-    TEMPDIR = tempfile.gettempdir()
-TEMPDIR = os.path.abspath(TEMPDIR)
-
-
 class Regrtest:
     """Execute a test suite.
 
@@ -98,7 +81,10 @@
         # used by --junit-xml
         self.testsuite_xml = None
 
+        # misc
         self.win_load_tracker = None
+        self.tmp_dir = None
+        self.worker_test_name = None
 
     def get_executed(self):
         return (set(self.good) | set(self.bad) | set(self.skipped)
@@ -177,6 +163,13 @@
         if ns.xmlpath:
             support.junit_xml_list = self.testsuite_xml = []
 
+        worker_args = ns.worker_args
+        if worker_args is not None:
+            from test.libregrtest.runtest_mp import parse_worker_args
+            ns, test_name = parse_worker_args(ns.worker_args)
+            ns.worker_args = worker_args
+            self.worker_test_name = test_name
+
         # Strip .py extensions.
         removepy(ns.args)
 
@@ -186,7 +179,7 @@
         self.tests = tests
 
         if self.ns.single:
-            self.next_single_filename = os.path.join(TEMPDIR, 'pynexttest')
+            self.next_single_filename = os.path.join(self.tmp_dir, 'pynexttest')
             try:
                 with open(self.next_single_filename, 'r') as fp:
                     next_test = fp.read().strip()
@@ -544,29 +537,54 @@
             for s in ET.tostringlist(root):
                 f.write(s)
 
-    def main(self, tests=None, **kwargs):
-        global TEMPDIR
-        self.ns = self.parse_args(kwargs)
-
+    def create_temp_dir(self):
         if self.ns.tempdir:
-            TEMPDIR = self.ns.tempdir
-        elif self.ns.worker_args:
-            ns_dict, _ = json.loads(self.ns.worker_args)
-            TEMPDIR = ns_dict.get("tempdir") or TEMPDIR
+            self.tmp_dir = self.ns.tempdir
 
-        os.makedirs(TEMPDIR, exist_ok=True)
+        if not self.tmp_dir:
+            # When tests are run from the Python build directory, it is best practice
+            # to keep the test files in a subfolder.  This eases the cleanup of leftover
+            # files using the "make distclean" command.
+            if sysconfig.is_python_build():
+                self.tmp_dir = sysconfig.get_config_var('abs_builddir')
+                if self.tmp_dir is None:
+                    # bpo-30284: On Windows, only srcdir is available. Using
+                    # abs_builddir mostly matters on UNIX when building Python
+                    # out of the source tree, especially when the source tree
+                    # is read only.
+                    self.tmp_dir = sysconfig.get_config_var('srcdir')
+                self.tmp_dir = os.path.join(self.tmp_dir, 'build')
+            else:
+                self.tmp_dir = tempfile.gettempdir()
+
+        self.tmp_dir = os.path.abspath(self.tmp_dir)
+        os.makedirs(self.tmp_dir, exist_ok=True)
 
         # Define a writable temp dir that will be used as cwd while running
         # the tests. The name of the dir includes the pid to allow parallel
         # testing (see the -j option).
-        test_cwd = 'test_python_{}'.format(os.getpid())
-        test_cwd = os.path.join(TEMPDIR, test_cwd)
+        pid = os.getpid()
+        if self.worker_test_name is not None:
+            test_cwd = 'worker_{}'.format(pid)
+        else:
+            test_cwd = 'test_python_{}'.format(pid)
+        test_cwd = os.path.join(self.tmp_dir, test_cwd)
+        return test_cwd
 
-        # Run the tests in a context manager that temporarily changes the CWD to a
-        # temporary and writable directory.  If it's not possible to create or
-        # change the CWD, the original CWD will be used.  The original CWD is
-        # available from support.SAVEDCWD.
+    def main(self, tests=None, **kwargs):
+        self.ns = self.parse_args(kwargs)
+
+        test_cwd = self.create_temp_dir()
+
+        # Run the tests in a context manager that temporarily changes the CWD
+        # to a temporary and writable directory. If it's not possible to
+        # create or change the CWD, the original CWD will be used.
+        # The original CWD is available from support.SAVEDCWD.
         with support.temp_cwd(test_cwd, quiet=True):
+            # When using multiprocessing, worker processes will use test_cwd
+            # as their parent temporary directory. So when the main process
+            # exit, it removes also subdirectories of worker processes.
+            self.ns.tempdir = test_cwd
             self._main(tests, kwargs)
 
     def getloadavg(self):
@@ -588,9 +606,9 @@
                 print(msg, file=sys.stderr, flush=True)
                 sys.exit(2)
 
-        if self.ns.worker_args is not None:
+        if self.worker_test_name is not None:
             from test.libregrtest.runtest_mp import run_tests_worker
-            run_tests_worker(self.ns.worker_args)
+            run_tests_worker(self.ns, self.worker_test_name)
 
         if self.ns.wait:
             input("Press any key to continue...")
@@ -611,7 +629,7 @@
 
         # If we're on windows and this is the parent runner (not a worker),
         # track the load average.
-        if sys.platform == 'win32' and (self.ns.worker_args is None):
+        if sys.platform == 'win32' and self.worker_test_name is None:
             from test.libregrtest.win_utils import WindowsLoadTracker
 
             try:
diff --git a/Lib/test/libregrtest/runtest_mp.py b/Lib/test/libregrtest/runtest_mp.py
index 4217847..aa2409b 100644
--- a/Lib/test/libregrtest/runtest_mp.py
+++ b/Lib/test/libregrtest/runtest_mp.py
@@ -33,6 +33,12 @@
     return False
 
 
+def parse_worker_args(worker_args):
+    ns_dict, test_name = json.loads(worker_args)
+    ns = types.SimpleNamespace(**ns_dict)
+    return (ns, test_name)
+
+
 def run_test_in_subprocess(testname, ns):
     ns_dict = vars(ns)
     worker_args = (ns_dict, testname)
@@ -42,8 +48,6 @@
            '-u',    # Unbuffered stdout and stderr
            '-m', 'test.regrtest',
            '--worker-args', worker_args]
-    if ns.pgo:
-        cmd += ['--pgo']
 
     # Running the child from the same working directory as regrtest's original
     # invocation ensures that TEMPDIR for the child is the same when
@@ -56,15 +60,15 @@
                             cwd=support.SAVEDCWD)
 
 
-def run_tests_worker(worker_args):
-    ns_dict, testname = json.loads(worker_args)
-    ns = types.SimpleNamespace(**ns_dict)
-
+def run_tests_worker(ns, test_name):
     setup_tests(ns)
 
-    result = runtest(ns, testname)
+    result = runtest(ns, test_name)
+
     print()   # Force a newline (just in case)
-    print(json.dumps(result), flush=True)
+
+    # Serialize TestResult as list in JSON
+    print(json.dumps(list(result)), flush=True)
     sys.exit(0)
 
 
diff --git a/Misc/NEWS.d/next/Tests/2019-05-14-14-12-24.bpo-36915.58b7pH.rst b/Misc/NEWS.d/next/Tests/2019-05-14-14-12-24.bpo-36915.58b7pH.rst
new file mode 100644
index 0000000..4eebfb4
--- /dev/null
+++ b/Misc/NEWS.d/next/Tests/2019-05-14-14-12-24.bpo-36915.58b7pH.rst
@@ -0,0 +1,3 @@
+The main regrtest process now always removes all temporary directories of
+worker processes even if they crash or if they are killed on
+KeyboardInterrupt (CTRL+c).