ninja/mac: Allow more than one ld process at a time, based on available RAM.

pylib/gyp/generator/ninja.py

 # Copyright (c) 2013 Google Inc. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import copy
 import hashlib
 import multiprocessing
 import os.path
 import re
 import signal
@@ skipping 1477 matching lines @@
   elif sys.platform.startswith('linux'):
     with open("/proc/meminfo") as meminfo:
       memtotal_re = re.compile(r'^MemTotal:\s*(\d*)\s*kB')
       for line in meminfo:
         match = memtotal_re.match(line)
         if not match:
           continue
         # Allow 8Gb per link on Linux because Gold is quite memory hungry
         return max(1, int(match.group(1)) / (8 * (2 ** 20)))
     return 1
+  elif sys.platform == 'darwin':
+    try:
+      avail_bytes = int(subprocess.check_output(['sysctl', '-n', 'hw.memsize']))
+      # A static library debug build of Chromium's unit_tests takes ~2.7GB, so
+      # 4GB per ld process allows for some more bloat.
+      return max(1, avail_bytes / (4 * (2 ** 30)))  # total / 4GB
+    except:
+      return 1
   else:
     # TODO(scottmg): Implement this for other platforms.
     return 1
 
 
 def _GetWinLinkRuleNameSuffix(embed_manifest, link_incremental):
   """Returns the suffix used to select an appropriate linking rule depending on
   whether the manifest embedding and/or incremental linking is enabled."""
   suffix = ''
   if embed_manifest:
@@ skipping 561 matching lines @@
           arglists.append(
               (target_list, target_dicts, data, params, config_name))
         pool.map(CallGenerateOutputForConfig, arglists)
       except KeyboardInterrupt, e:
         pool.terminate()
         raise e
     else:
       for config_name in config_names:
         GenerateOutputForConfig(target_list, target_dicts, data, params,
                                 config_name)