From df6ecc051873ad8c7450f933e74aea0775ea6e72 Mon Sep 17 00:00:00 2001 From: Vinay Sajip Date: Wed, 28 Sep 2022 05:17:42 +0100 Subject: [PATCH] gh-65046: Add note about logging from async code. (GH-97602) (cherry picked from commit 5c110d112600b679b4cf41b11d2b73653da60555) Co-authored-by: Vinay Sajip --- Doc/howto/logging-cookbook.rst | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/Doc/howto/logging-cookbook.rst b/Doc/howto/logging-cookbook.rst index 16df3b730ac80e..5b079744df12ed 100644 --- a/Doc/howto/logging-cookbook.rst +++ b/Doc/howto/logging-cookbook.rst @@ -397,6 +397,14 @@ which, when run, will produce: MainThread: Look out! +.. note:: Although the earlier discussion wasn't specifically talking about + async code, but rather about slow logging handlers, it should be noted that + when logging from async code, network and even file handlers could lead to + problems (blocking the event loop) because some logging is done from + :mod:`asyncio` internals. It might be best, if any async code is used in an + application, to use the above approach for logging, so that any blocking code + runs only in the ``QueueListener`` thread. + .. versionchanged:: 3.5 Prior to Python 3.5, the :class:`QueueListener` always passed every message received from the queue to every handler it was initialized with. (This was