From: Antoine Pitrou <solipsis@pitrou.net>
Date: Sun, 10 Apr 2011 22:26:42 +0000 (+0200)
Subject: Issue #8428: Fix a race condition in multiprocessing.Pool when terminating
X-Git-Tag: v2.7.2rc1~175
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=7dfc874a48516e58e830b3a455fca34c8cd834eb;p=python

Issue #8428: Fix a race condition in multiprocessing.Pool when terminating
worker processes: new processes would be spawned while the pool is being
shut down.  Patch by Charles-François Natali.
---

diff --git a/Lib/multiprocessing/pool.py b/Lib/multiprocessing/pool.py
index 1f366f035e..862a60e92c 100644
--- a/Lib/multiprocessing/pool.py
+++ b/Lib/multiprocessing/pool.py
@@ -295,6 +295,8 @@ class Pool(object):
         while pool._worker_handler._state == RUN and pool._state == RUN:
             pool._maintain_pool()
             time.sleep(0.1)
+        # send sentinel to stop workers
+        pool._taskqueue.put(None)
         debug('worker handler exiting')
 
     @staticmethod
@@ -413,7 +415,6 @@ class Pool(object):
         if self._state == RUN:
             self._state = CLOSE
             self._worker_handler._state = CLOSE
-            self._taskqueue.put(None)
 
     def terminate(self):
         debug('terminating pool')
@@ -447,7 +448,6 @@ class Pool(object):
 
         worker_handler._state = TERMINATE
         task_handler._state = TERMINATE
-        taskqueue.put(None)                 # sentinel
 
         debug('helping task handler/workers to finish')
         cls._help_stuff_finish(inqueue, task_handler, len(pool))
@@ -457,6 +457,11 @@ class Pool(object):
         result_handler._state = TERMINATE
         outqueue.put(None)                  # sentinel
 
+        # We must wait for the worker handler to exit before terminating
+        # workers because we don't want workers to be restarted behind our back.
+        debug('joining worker handler')
+        worker_handler.join()
+
         # Terminate workers which haven't already finished.
         if pool and hasattr(pool[0], 'terminate'):
             debug('terminating workers')
diff --git a/Misc/NEWS b/Misc/NEWS
index ee75bdad2c..5eb38dabd8 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -51,6 +51,10 @@ Core and Builtins
 Library
 -------
 
+- Issue #8428: Fix a race condition in multiprocessing.Pool when terminating
+  worker processes: new processes would be spawned while the pool is being
+  shut down.  Patch by Charles-François Natali.
+
 - Issue #7311: fix HTMLParser to accept non-ASCII attribute values.
 
 - Issue #10963: Ensure that subprocess.communicate() never raises EPIPE.