From 879d8b76e224ff23cbb74964b8b6dac1f288408c Mon Sep 17 00:00:00 2001 From: Duane Griffin Date: Fri, 27 Jun 2025 02:18:32 +1200 Subject: [PATCH] gh-91555: add warning to docs about possibility of deadlock/infinite recursion (GH-135954) * gh-91555: add warning to docs about possibility of deadlock/infinite recursion Attempt to clarify in the documentation that care must be taken when using multiprocessing classes to implement logging since they have builtin internal logging, and hence may cause deadlock/infinite recursion. * Update Doc/library/logging.handlers.rst Co-authored-by: Vinay Sajip * Change whitespace. --------- (cherry picked from commit a4625d597f9fc2d083fbb9c22d3ffcec73b2061a) Co-authored-by: Duane Griffin Co-authored-by: Vinay Sajip --- Doc/library/logging.handlers.rst | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/Doc/library/logging.handlers.rst b/Doc/library/logging.handlers.rst index 8f3aa1dfdd0cde..d74ef73ee28497 100644 --- a/Doc/library/logging.handlers.rst +++ b/Doc/library/logging.handlers.rst @@ -1059,6 +1059,15 @@ possible, while any potentially slow operations (such as sending an email via .. note:: If you are using :mod:`multiprocessing`, you should avoid using :class:`~queue.SimpleQueue` and instead use :class:`multiprocessing.Queue`. + .. warning:: + + The :mod:`multiprocessing` module uses an internal logger created and + accessed via :meth:`~multiprocessing.get_logger`. + :class:`multiprocessing.Queue` will log ``DEBUG`` level messages upon + items being queued. If those log messages are processed by a + :class:`QueueHandler` using the same :class:`multiprocessing.Queue` instance, + it will cause a deadlock or infinite recursion. + .. method:: emit(record) Enqueues the result of preparing the LogRecord. Should an exception