bpo-30301: Fix AttributeError when using SimpleQueue.empty() (#1601) (#1628)
Under *spawn* and *forkserver* start methods, SimpleQueue.empty() could
raise AttributeError due to not setting _poll in __setstate__.
diff --git a/Lib/multiprocessing/queues.py b/Lib/multiprocessing/queues.py
index dda03dd..a4f4ef8 100644
--- a/Lib/multiprocessing/queues.py
+++ b/Lib/multiprocessing/queues.py
@@ -337,6 +337,7 @@
def __setstate__(self, state):
(self._reader, self._writer, self._rlock, self._wlock) = state
+ self._poll = self._reader.poll
def get(self):
with self._rlock:
diff --git a/Lib/test/_test_multiprocessing.py b/Lib/test/_test_multiprocessing.py
index 57ada12..3eb83c5 100644
--- a/Lib/test/_test_multiprocessing.py
+++ b/Lib/test/_test_multiprocessing.py
@@ -3958,6 +3958,42 @@
self.assertRegex(err, expected)
self.assertRegex(err, r'semaphore_tracker: %r: \[Errno' % name1)
+class TestSimpleQueue(unittest.TestCase):
+
+ @classmethod
+ def _test_empty(cls, queue, child_can_start, parent_can_continue):
+ child_can_start.wait()
+ # issue 30301, could fail under spawn and forkserver
+ try:
+ queue.put(queue.empty())
+ queue.put(queue.empty())
+ finally:
+ parent_can_continue.set()
+
+ def test_empty(self):
+ queue = multiprocessing.SimpleQueue()
+ child_can_start = multiprocessing.Event()
+ parent_can_continue = multiprocessing.Event()
+
+ proc = multiprocessing.Process(
+ target=self._test_empty,
+ args=(queue, child_can_start, parent_can_continue)
+ )
+ proc.daemon = True
+ proc.start()
+
+ self.assertTrue(queue.empty())
+
+ child_can_start.set()
+ parent_can_continue.wait()
+
+ self.assertFalse(queue.empty())
+ self.assertEqual(queue.get(), True)
+ self.assertEqual(queue.get(), False)
+ self.assertTrue(queue.empty())
+
+ proc.join()
+
#
# Mixins
#