Add counting the number of CPU's in goma module

scripts/slave/recipe_modules/goma/api.py

 # Copyright 2015 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.
 
 from recipe_engine import recipe_api
 
 class GomaApi(recipe_api.RecipeApi):
   """GomaApi contains helper functions for using goma."""
 
   def __init__(self, **kwargs):
     super(GomaApi, self).__init__(**kwargs)
     self._goma_dir = None
     self._goma_started = False
 
     self._goma_ctl_env = {}
     self._cloudtail_pid = None
+    self._goma_jobs = None
 
   @property
   def service_account_json_path(self):
     if self.m.platform.is_win:
       return 'C:\\creds\\service_accounts\\service-account-goma-client.json'
     return '/creds/service_accounts/service-account-goma-client.json'
 
   @property
   def cloudtail_path(self):
     assert self._goma_dir
     return self.m.path.join(self._goma_dir, 'cloudtail')
 
   @property
   def json_path(self):
     assert self._goma_dir
     return self.m.path.join(self._goma_dir, 'jsonstatus')
 
+  @property
+  def recommended_goma_jobs(self):
+    """
+    Return the recommended number of jobs for parallel build using Goma.
+
+    This function caches the _goma_jobs.
+    """
+    if self._goma_jobs:
+      return self._goma_jobs
+
+    step_result = self.m.python.inline(

[shinyak, 2016/09/07 05:03:59]

could you write down why we need to use inline python here? It's not so
intuitive.

[tikuta, 2016/09/07 05:12:44]

Done.

+      'calculate the number of recommended jobs',
+      """
+import multiprocessing
+import sys
+
+job_limit = 200
+if sys.platform.startswith('linux'):
+  # Use 80 for linux not to load goma backend.
+  job_limit = 80
+
+try:
+  jobs = min(job_limit, multiprocessing.cpu_count() * 10)
+except NotImplementedError:
+  jobs = 50
+
+print jobs
+      """,
+      stdout=self.m.raw_io.output(),
+      step_test_data=(
+          lambda: self.m.raw_io.test_api.stream_output('50\n'))
+    )
+    self._goma_jobs = int(step_result.stdout)
+
+    return self._goma_jobs
+
   def ensure_goma(self, canary=False):
     with self.m.step.nest('ensure_goma'):
       with self.m.step.context({'infra_step': True}):
         try:
           self.m.cipd.set_service_account_credentials(
               self.service_account_json_path)
 
           self.m.cipd.install_client()
           goma_package = ('infra_internal/goma/client/%s' %
               self.m.cipd.platform_suffix())
@@ skipping 196 matching lines @@
         ])
 
 
     self.m.python(
       name=name or 'upload_log',
       script=self.package_repo_resource(
           'scripts', 'slave', 'upload_goma_logs.py'),
       args=args,
       env=self._goma_ctl_env
     )