[Findit] Make Findit more robust.

tools/findit/crash_utils.py

 # Copyright (c) 2014 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.
 
+import atexit
 import cgi
 import ConfigParser
 import json
 import os
 import Queue
 import threading
 import time
 
 from common import utils
 from result import Result
 
 
 INFINITY = float('inf')
 
 MAX_THREAD_NUMBER = 10
 TASK_QUEUE = None
 
 
+def SignalWorkerThreads():
+  global TASK_QUEUE
+  if not TASK_QUEUE:
+    return
+
+  for i in range(MAX_THREAD_NUMBER):
+    TASK_QUEUE.put(None)
+
+  # Give worker threads a chance to exit.
+  # Workaround the harmless bug in python 2.7 below.
+  time.sleep(1)
+  print '%s is quitting' % threading.currentThread().name
+
+
+atexit.register(SignalWorkerThreads)
+
+
 def Worker():
   global TASK_QUEUE
   while True:
-    function, args, kwargs, result_semaphore = TASK_QUEUE.get()

[stgao, 2014/09/05 08:33:18]

The exception is as below:

Exception in thread worker_9 (most likely raised during interpreter shutdown):  

Traceback (most recent call last):                                              

  File "/usr/lib/python2.7/threading.py", line 808, in __bootstrap_inner        

  File "/usr/lib/python2.7/threading.py", line 761, in run                      

  File "/mnt/scratch0/clusterfuzz/src/tools/findit/crash_utils.py", line 26, in
Worker
  File "/usr/lib/python2.7/Queue.py", line 168, in get                          

  File "/usr/lib/python2.7/threading.py", line 332, in wait                     

<type 'exceptions.TypeError'>: 'NoneType' object is not callable  

+    try:
+      task = TASK_QUEUE.get()
+      if not task:
+        print '%s is quitting' % threading.currentThread().name

[stgao, 2014/09/05 08:33:18]

I will revert the print before committing.
But I'd like to show this fix will work, because the order of quitting is as
below:

worker_3 is quitting
 worker_2 is quitting
 worker_7 is quitting
worker_1 is quitting
worker_6 is quitting
 worker_8 is quitting
worker_5 is quitting
worker_9 is quitting
 worker_0 is quitting
worker_4 is quitting
Dummy-1 is quitting

+        return
+    except TypeError:
+      # According to http://bugs.python.org/issue14623, this is a harmless bug
+      # in python 2.7 which won't be fixed.
+      # The exception is raised on daemon threads when python interpreter is
+      # shutting down.
+      return
+
+    function, args, kwargs, result_semaphore = task
     try:
       function(*args, **kwargs)
     except:
       pass
     finally:
       # Signal one task is done in case of exception.
       result_semaphore.release()
 
 
 def RunTasks(tasks):
@@ skipping 517 matching lines @@
     review_url = None
     reviewers = None
     line_content = blame.line_content
     message = blame.message
 
     result = Result(suspected_cl, revision_url, component_name, author, reason,
                     review_url, reviewers, line_content, message)
     result_list.append(result)
 
   return result_list