Changes to improve multiprocessing PRESUBMIT support in Windows

presubmit_support.py

 #!/usr/bin/env python
 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Enables directory-specific presubmit checks to run at upload and/or commit.
 """
 
 __version__ = '1.8.0'
 
@@ skipping 295 matching lines @@
 
     # To easily fork python.
     self.python_executable = sys.executable
     self.environ = os.environ
 
     # InputApi.platform is the platform you're currently running on.
     self.platform = sys.platform
 
     self.cpu_count = multiprocessing.cpu_count()
 
+    # this is done here because in RunTests, the current working directory has
+    # changed, which causes Pool() to explode fantastically when run on windows
+    # (because it tries to load the __main__ module, which imports lots of
+    # things relative to the current working directory).
+    self._run_tests_pool = multiprocessing.Pool(self.cpu_count)

[iannucci, 2015/06/28 19:47:43]

this is so we pick up the mocked cpu_count

+
     # The local path of the currently-being-processed presubmit script.
     self._current_presubmit_path = os.path.dirname(presubmit_path)
 
     # We carry the canned checks so presubmit scripts can easily use them.
     self.canned_checks = presubmit_canned_checks
 
     # TODO(dpranke): figure out a list of all approved owners for a repo
     # in order to be able to handle wildcard OWNERS files?
     self.owners_db = owners.Database(change.RepositoryRoot(),
         fopen=file, os_path=self.os_path, glob=self.glob)
@@ skipping 159 matching lines @@
     msgs = []
     for t in tests_mix:
       if isinstance(t, OutputApi.PresubmitResult):
         msgs.append(t)
       else:
         assert issubclass(t.message, _PresubmitResult)
         tests.append(t)
         if self.verbose:
           t.info = _PresubmitNotifyResult
     if len(tests) > 1 and parallel:
-      pool = multiprocessing.Pool()
       # async recipe works around multiprocessing bug handling Ctrl-C
-      msgs.extend(pool.map_async(CallCommand, tests).get(99999))
-      pool.close()
-      pool.join()
+      msgs.extend(self._run_tests_pool.map_async(CallCommand, tests).get(99999))
     else:
       msgs.extend(map(CallCommand, tests))
     return [m for m in msgs if m]
 
 
 class _DiffCache(object):
   """Caches diffs retrieved from a particular SCM."""
   def __init__(self, upstream=None):
     """Stores the upstream revision against which all diffs will be computed."""
     self._upstream = upstream
@@ skipping 1238 matching lines @@
     return 2
 
 
 if __name__ == '__main__':
   fix_encoding.fix_encoding()
   try:
     sys.exit(main())
   except KeyboardInterrupt:
     sys.stderr.write('interrupted\n')
     sys.exit(1)