Add a git cache for gclient sync operations.

gclient.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.
 
 """Meta checkout manager supporting both Subversion and GIT.
 
 Files
   .gclient      : Current client configuration, written by 'config' command.
                   Format is a Python script defining 'solutions', a list whose
@@ skipping 48 matching lines @@
   If the "target_os_only" key is also present and true, then *only* the
   operating systems listed in "target_os" will be used.
 
   Example:
     target_os = [ "ios" ]
     target_os_only = True
 """
 
 __version__ = "0.6.4"
 
+import collections
 import copy
 import logging
 import optparse
 import os
 import platform
 import posixpath
 import pprint
 import re
 import sys
+import threading
 import urllib
 import urlparse
 
 import breakpad  # pylint: disable=W0611
 
 import fix_encoding
 import gclient_scm
 import gclient_utils
 from third_party.repo.progress import Progress
 import subprocess2
@@ skipping 1448 matching lines @@
                          'fast-forward or rebase')
   parser.add_option('--deps', dest='deps_os', metavar='OS_LIST',
                     help='override deps for the specified (comma-separated) '
                          'platform(s); \'all\' will process all deps_os '
                          'references')
   parser.add_option('-m', '--manually_grab_svn_rev', action='store_true',
                     help='Skip svn up whenever possible by requesting '
                          'actual HEAD revision from the repository')
   parser.add_option('--upstream', action='store_true',
                     help='Make repo state match upstream branch.')
+  parser.add_option('--cache-dir',
+                    help='For git, cache all repos into this dir and do shared '
+                         'clones from the cache, instead of cloning directly '
+                         'from the remote.')
   (options, args) = parser.parse_args(args)
   client = GClient.LoadCurrentConfig(options)
 
+  if options.cache_dir:
+    # If a given cache is used in a solution more than once, prevent multiple
+    # threads from updating it simultaneously. |cache_lock| is used to prevent
+    # races on the defaultdict's construction of Locks.
+    options.cache_lock = threading.Lock()

[szager1, 2013/07/01 23:38:29]

options.cache_lock shouldn't be necessary; vivifying a new entry in
options.cache_locks is thread-safe and atomic, because threading.Lock is a
built-in type. 

[iannucci, 2013/07/01 23:55:52]

defaultdict guarantees that item addition is atomic?

In that case, I'm happy to ditch the uberlock.

[szager1, 2013/07/02 00:08:05]

As long as the __init__ method for the subject class is atomic (which is true
for all built-in types, including threading.Lock), defaultdict is thread-safe.

+    options.cache_locks = collections.defaultdict(threading.Lock)
+
   if not client:
     raise gclient_utils.Error('client not configured; see \'gclient config\'')
 
   if options.revisions and options.head:
     # TODO(maruel): Make it a parser.error if it doesn't break any builder.
     print('Warning: you cannot use both --head and --revision')
 
   if options.verbose:
     # Print out the .gclient file.  This is longer than if we just printed the
     # client dict, but more legible, and it might contain helpful comments.
@@ skipping 248 matching lines @@
   except (gclient_utils.Error, subprocess2.CalledProcessError), e:
     print >> sys.stderr, 'Error: %s' % str(e)
     return 1
 
 
 if '__main__' == __name__:
   fix_encoding.fix_encoding()
   sys.exit(Main(sys.argv[1:]))
 
 # vim: ts=2:sw=2:tw=80:et: