bpo-36813: Fix QueueListener to call task_done() upon termination. (GH-13113)

Fixed QueueListener in order to avoid random deadlocks.
Unable to add regression tests atm due to time constraints, will add it in a bit.
Regarding implementation, although it's nested, it does not cause performance issues whatsoever, and does not call task_done() in case of an exception (which is the right thing to do IMHO).


https://bugs.python.org/issue36813

1 files changed, 10 insertions, 0 deletions

diff --git a/Lib/test/test_logging.py b/Lib/test/test_logging.py
index b884753ad3..50148dc2f2 100644
--- a/Lib/test/test_logging.py
+++ b/Lib/test/test_logging.py
@@ -3633,6 +3633,16 @@ if hasattr(logging.handlers, 'QueueListener'):
                                     [m.msg if isinstance(m, logging.LogRecord)
                                      else m for m in items]))
 
+        def test_calls_task_done_after_stop(self):
+            # Issue 36813: Make sure queue.join does not deadlock.
+            log_queue = queue.Queue()
+            listener = logging.handlers.QueueListener(log_queue)
+            listener.start()
+            listener.stop()
+            with self.assertRaises(ValueError):
+                # Make sure all tasks are done and .join won't block.
+                log_queue.task_done()
+
 
 ZERO = datetime.timedelta(0)