pythongh-91555: add warning to docs about possibility of deadlock/infinite recursion (pythonGH-135954)

duaneg · vsajip · miss-islington · commit 879d8b76e224 · 2025-06-26T14:18:59.000Z
* pythongh-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 <vinay_sajip@yahoo.co.uk> * Change whitespace. --------- (cherry picked from commit a4625d5) Co-authored-by: Duane Griffin <duaneg@dghda.com> Co-authored-by: Vinay Sajip <vinay_sajip@yahoo.co.uk>
diff --git 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
