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Apr 13, 2025
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[3.13] gh-132106: Ensure that running `logging.handlers.QueueListener… #132471

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[3.13] gh-132106: Ensure that running `logging.handlers.QueueListener…
csm10495 Apr 13, 2025
87c7e67
Tidy up tests.
vsajip Apr 13, 2025
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4 changes: 4 additions & 0 deletions Doc/library/logging.handlers.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -1172,6 +1172,10 @@ possible, while any potentially slow operations (such as sending an email via
This starts up a background thread to monitor the queue for
LogRecords to process.

.. versionchanged:: next
Raises :exc:`RuntimeError` if called and the listener is already
running.

.. method:: stop()

Stops the listener.
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3 changes: 3 additions & 0 deletions Lib/logging/handlers.py
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Expand Up @@ -1545,6 +1545,9 @@ def start(self):
This starts up a background thread to monitor the queue for
LogRecords to process.
"""
if self._thread is not None:
raise RuntimeError("Listener already started")

self._thread = t = threading.Thread(target=self._monitor)
t.daemon = True
t.start()
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18 changes: 12 additions & 6 deletions Lib/test/test_logging.py
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Expand Up @@ -4300,8 +4300,6 @@ def test_formatting(self):
self.assertEqual(formatted_msg, log_record.msg)
self.assertEqual(formatted_msg, log_record.message)

@unittest.skipUnless(hasattr(logging.handlers, 'QueueListener'),
'logging.handlers.QueueListener required for this test')
def test_queue_listener(self):
handler = TestHandler(support.Matcher())
listener = logging.handlers.QueueListener(self.queue, handler)
Expand Down Expand Up @@ -4336,8 +4334,18 @@ def test_queue_listener(self):
self.assertTrue(handler.matches(levelno=logging.CRITICAL, message='6'))
handler.close()

@unittest.skipUnless(hasattr(logging.handlers, 'QueueListener'),
'logging.handlers.QueueListener required for this test')
# doesn't hurt to call stop() more than once.
listener.stop()
self.assertIsNone(listener._thread)

def test_queue_listener_multi_start(self):
handler = TestHandler(support.Matcher())
listener = logging.handlers.QueueListener(self.queue, handler)
listener.start()
self.assertRaises(RuntimeError, listener.start)
listener.stop()
self.assertIsNone(listener._thread)

def test_queue_listener_with_StreamHandler(self):
# Test that traceback and stack-info only appends once (bpo-34334, bpo-46755).
listener = logging.handlers.QueueListener(self.queue, self.root_hdlr)
Expand All @@ -4352,8 +4360,6 @@ def test_queue_listener_with_StreamHandler(self):
self.assertEqual(self.stream.getvalue().strip().count('Traceback'), 1)
self.assertEqual(self.stream.getvalue().strip().count('Stack'), 1)

@unittest.skipUnless(hasattr(logging.handlers, 'QueueListener'),
'logging.handlers.QueueListener required for this test')
def test_queue_listener_with_multiple_handlers(self):
# Test that queue handler format doesn't affect other handler formats (bpo-35726).
self.que_hdlr.setFormatter(self.root_formatter)
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2025-04-12-09-30-24.gh-issue-132106.OxUds3.rst
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@@ -0,0 +1,2 @@
:meth:`QueueListener.start <logging.handlers.QueueListener.start>` now
raises a :exc:`RuntimeError` if the listener is already started.
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