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 ff7c29c..efa0056 100644
--- a/Lib/multiprocessing/pool.py
+++ b/Lib/multiprocessing/pool.py
@@ -322,6 +322,8 @@
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
@@ -440,7 +442,6 @@
if self._state == RUN:
self._state = CLOSE
self._worker_handler._state = CLOSE
- self._taskqueue.put(None)
def terminate(self):
debug('terminating pool')
@@ -474,7 +475,6 @@
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))
@@ -484,6 +484,11 @@
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')