Make gclient sync use cpu count for default jobs

- On high core, fast machines, jobs=8 is does not offer good
  parallelization.  Switch to use number of local cpus.

R=maruel@chromium.org
BUG=


Review URL: https://chromiumcodereview.appspot.com/11140019

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@162072 0039d316-1c4b-4281-b951-d872f2087c98

gclient.py

@@ -1541,11 +1541,11 @@ def Parser():
   if platform.machine().startswith('arm'):
     jobs = 1
   else:
-    jobs = 8
+    jobs = max(8, gclient_utils.NumLocalCpus())
   gclientfile_default = os.environ.get('GCLIENT_FILE', '.gclient')
   parser.add_option('-j', '--jobs', default=jobs, type='int',
                     help='Specify how many SCM commands can run in parallel; '
-                          'default=%default')
+                          'defaults to number of cpu cores (%default)')
   parser.add_option('-v', '--verbose', action='count', default=0,
                     help='Produces additional output for diagnostics. Can be '
                           'used up to three times for more logging info.')

gclient_utils.py

@@ -769,3 +769,17 @@ def ParseCodereviewSettingsContent(content):
   fix_url('CODE_REVIEW_SERVER')
   fix_url('VIEW_VC')
   return keyvals
+
+
+def NumLocalCpus():
+  """Returns the number of processors.
+
+  Python on OSX 10.6 raises a NotImplementedError exception.
+  """
+  try:
+    import multiprocessing
+    return multiprocessing.cpu_count()
+  except:  # pylint: disable=W0702
+    # Mac OS 10.6 only
+    # pylint: disable=E1101
+    return int(os.sysconf('SC_NPROCESSORS_ONLN'))

tests/gclient_utils_test.py

@@ -33,7 +33,7 @@ class GclientUtilsUnittest(GclientUtilBase):
         'FileWrite', 'FindFileUpwards', 'FindGclientRoot',
         'GetGClientRootAndEntries', 'GetEditor', 'IsDateRevision',
         'MakeDateRevision', 'MakeFileAutoFlush', 'MakeFileAnnotated',
-        'PathDifference', 'ParseCodereviewSettingsContent',
+        'PathDifference', 'ParseCodereviewSettingsContent', 'NumLocalCpus',
         'PrintableObject', 'RemoveDirectory', 'RunEditor',
         'SplitUrlRevision', 'SyntaxErrorToError',
         'UpgradeToHttps', 'Wrapper', 'WorkItem',