diff --git a/Lib/multiprocessing/pool.py b/Lib/multiprocessing/pool.py index b223d6aa724bb6..41dd923d4f9740 100644 --- a/Lib/multiprocessing/pool.py +++ b/Lib/multiprocessing/pool.py @@ -651,8 +651,6 @@ def close(self): def terminate(self): util.debug('terminating pool') self._state = TERMINATE - self._worker_handler._state = TERMINATE - self._change_notifier.put(None) self._terminate() def join(self): @@ -682,7 +680,12 @@ def _terminate_pool(cls, taskqueue, inqueue, outqueue, pool, change_notifier, # this is guaranteed to only be called once util.debug('finalizing pool') + # Notify that the worker_handler state has been changed so the + # _handle_workers loop can be unblocked (and exited) in order to + # send the finalization sentinel all the workers. worker_handler._state = TERMINATE + change_notifier.put(None) + task_handler._state = TERMINATE util.debug('helping task handler/workers to finish') diff --git a/Lib/test/_test_multiprocessing.py b/Lib/test/_test_multiprocessing.py index b985d51508cb75..4a87b1761f9efe 100644 --- a/Lib/test/_test_multiprocessing.py +++ b/Lib/test/_test_multiprocessing.py @@ -2780,6 +2780,24 @@ def test_pool_worker_lifetime_early_close(self): for (j, res) in enumerate(results): self.assertEqual(res.get(), sqr(j)) + def test_worker_finalization_via_atexit_handler_of_multiprocessing(self): + # tests cases against bpo-38744 and bpo-39360 + cmd = '''if 1: + from multiprocessing import Pool + problem = None + class A: + def __init__(self): + self.pool = Pool(processes=1) + def test(): + global problem + problem = A() + problem.pool.map(float, tuple(range(10))) + if __name__ == "__main__": + test() + ''' + rc, out, err = test.support.script_helper.assert_python_ok('-c', cmd) + self.assertEqual(rc, 0) + # # Test of creating a customized manager class # diff --git a/Misc/NEWS.d/next/Library/2020-03-15-05-41-05.bpo-39360.cmcU5p.rst b/Misc/NEWS.d/next/Library/2020-03-15-05-41-05.bpo-39360.cmcU5p.rst new file mode 100644 index 00000000000000..148878886e6ee5 --- /dev/null +++ b/Misc/NEWS.d/next/Library/2020-03-15-05-41-05.bpo-39360.cmcU5p.rst @@ -0,0 +1,4 @@ +Ensure all workers exit when finalizing a :class:`multiprocessing.Pool` implicitly via the module finalization +handlers of multiprocessing. This fixes a deadlock situation that can be experienced when the Pool is not +properly finalized via the context manager or a call to ``multiprocessing.Pool.terminate``. Patch by Batuhan Taskaya +and Pablo Galindo.