Add cross-platform resilience to gclient CPU count probe.

gclient_utils.py

 # 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.
 
 """Generic utils."""
 
 import codecs
 import cStringIO
 import datetime
 import logging
@@ skipping 1116 matching lines @@
     if keyvals.get(key):
       keyvals[key] = UpgradeToHttps(keyvals[key])
   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.
+  multiprocessing.cpu_count() is permitted to raise NotImplementedError, and
+  is known to do this on some Windows systems and OSX 10.6. If we can't get the
+  CPU count, we will fall back to '1'.
   """
+  # Surround the entire thing in try/except; no failure here should stop gclient
+  # from working.
   try:

[agable, 2015/01/07 00:11:02]

This function is now:

try:
  try:
    return
  except:
    pass
  return
except:
  pass
return

Why not

try:
  try:
    return
  except:
    return
except:
  return

?

[dnj, 2015/01/07 00:49:23]

I'm generally adverse to large 'except' logic blocks, but sure!

-    import multiprocessing
-    return multiprocessing.cpu_count()
-  except:  # pylint: disable=W0702
-    # Mac OS 10.6 only
+    # Use multiprocessing to get CPU count. This may raise
+    # NotImplementedError.
+    try:
+      import multiprocessing
+      return multiprocessing.cpu_count()
+    except NotImplementedError:  # pylint: disable=W0702
+      pass
+
+    # (UNIX) Query 'os.sysconf'.
     # pylint: disable=E1101
-    return int(os.sysconf('SC_NPROCESSORS_ONLN'))
+    if hasattr(os, 'sysconf') and 'SC_NPROCESSORS_ONLN' in os.sysconf_names:
+      return int(os.sysconf('SC_NPROCESSORS_ONLN'))
+
+    # (Windows) Query 'NUMBER_OF_PROCESSORS' environment variable.
+    if 'NUMBER_OF_PROCESSORS' in os.environ:
+      return int(os.environ['NUMBER_OF_PROCESSORS'])
+  except Exception:
+    logging.exception("Exception raised while probing CPU count")
+
+  logging.debug('Failed to get CPU count. Defaulting to 1.')
+  return 1
 
 def DefaultDeltaBaseCacheLimit():
   """Return a reasonable default for the git config core.deltaBaseCacheLimit.
 
   The primary constraint is the address space of virtual memory.  The cache
   size limit is per-thread, and 32-bit systems can hit OOM errors if this
   parameter is set too high.
   """
   if platform.architecture()[0].startswith('64'):
     return '2g'
   else:
     return '512m'
 
 def DefaultIndexPackConfig(url=''):
   """Return reasonable default values for configuring git-index-pack.
 
   Experiments suggest that higher values for pack.threads don't improve
   performance."""
   cache_limit = DefaultDeltaBaseCacheLimit()
   result = ['-c', 'core.deltaBaseCacheLimit=%s' % cache_limit]
   if url in THREADED_INDEX_PACK_BLACKLIST:
     result.extend(['-c', 'pack.threads=1'])
   return result