Add thread locking around GetCachePath().

git_cache.py

 #!/usr/bin/env python
 # Copyright 2014 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.
 
 """A git command for managing a local cache of git repositories."""
 
 from __future__ import print_function
 import errno
 import logging
 import optparse
 import os
 import re
 import tempfile
+import threading
 import time
 import shutil
 import subprocess
 import sys
 import urlparse
 import zipfile
 
 from download_from_google_storage import Gsutil
 import gclient_utils
 import subcommand
@@ skipping 112 matching lines @@
     """Test if the file is locked by this process."""
     return self.is_locked() and self.pid == self._read_pid()
 
 
 class Mirror(object):
 
   git_exe = 'git.bat' if sys.platform.startswith('win') else 'git'
   gsutil_exe = os.path.join(
     os.path.dirname(os.path.abspath(__file__)),
     'third_party', 'gsutil', 'gsutil')
+  cachepath_lock = threading.Lock()
 
   def __init__(self, url, refs=None, print_func=None):
     self.url = url
     self.refs = refs or []
     self.basedir = self.UrlToCacheDir(url)
     self.mirror_path = os.path.join(self.GetCachePath(), self.basedir)
     self.print = print_func or print
 
   @property
   def bootstrap_bucket(self):
@@ skipping 38 matching lines @@
           if os.path.isfile(alt_target) and os.access(alt_target, os.X_OK):
             return alt_target
     return None
 
   @classmethod
   def SetCachePath(cls, cachepath):
     setattr(cls, 'cachepath', cachepath)
 
   @classmethod
   def GetCachePath(cls):
+    cls.cachepath_lock.acquire()
     if not hasattr(cls, 'cachepath'):
       try:
         cachepath = subprocess.check_output(
             [cls.git_exe, 'config', '--global', 'cache.cachepath']).strip()
       except subprocess.CalledProcessError:
         cachepath = None
       if not cachepath:
+        cls.cachepath_lock.release()
         raise RuntimeError('No global cache.cachepath git configuration found.')
       setattr(cls, 'cachepath', cachepath)
+      cls.cachepath_lock.release()
     return getattr(cls, 'cachepath')
 
   def RunGit(self, cmd, **kwargs):
     """Run git in a subprocess."""
     cwd = kwargs.setdefault('cwd', self.mirror_path)
     kwargs.setdefault('print_stdout', False)
     kwargs.setdefault('filter_fn', self.print)
     env = kwargs.get('env') or kwargs.setdefault('env', os.environ.copy())
     env.setdefault('GIT_ASKPASS', 'true')
     env.setdefault('SSH_ASKPASS', 'true')
@@ skipping 461 matching lines @@
     return options, args
 
 
 def main(argv):
   dispatcher = subcommand.CommandDispatcher(__name__)
   return dispatcher.execute(OptionParser(), argv)
 
 
 if __name__ == '__main__':
   sys.exit(main(sys.argv[1:]))