From 2e49b5254aa0888dd21a7929be14b6cfe03d56ef Mon Sep 17 00:00:00 2001 From: "Miss Islington (bot)" <31488909+miss-islington@users.noreply.github.com> Date: Fri, 10 Apr 2020 19:11:16 -0700 Subject: [PATCH] bpo-38501: Add a warning section to multiprocessing.Pool docs about resource managing (GH-19466) (cherry picked from commit 7ec43a73092d43c6c95e7dd2669f49d54b57966f) Co-authored-by: Pablo Galindo --- Doc/library/multiprocessing.rst | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/Doc/library/multiprocessing.rst b/Doc/library/multiprocessing.rst index 6fd509a00caf..1b850ebced5e 100644 --- a/Doc/library/multiprocessing.rst +++ b/Doc/library/multiprocessing.rst @@ -429,7 +429,8 @@ process which created it. >>> def f(x): ... return x*x ... - >>> p.map(f, [1,2,3]) + >>> with p: + ... p.map(f, [1,2,3]) Process PoolWorker-1: Process PoolWorker-2: Process PoolWorker-3: @@ -2100,6 +2101,16 @@ with the :class:`Pool` class. Note that the methods of the pool object should only be called by the process which created the pool. + .. warning:: + :class:`multiprocessing.pool` objects have internal resources that need to be + properly managed (like any other resource) by using the pool as a context manager + or by calling :meth:`close` and :meth:`terminate` manually. Failure to do this + can lead to the process hanging on finalization. + + Note that is **not correct** to rely on the garbage colletor to destroy the pool + as CPython does not assure that the finalizer of the pool will be called + (see :meth:`object.__del__` for more information). + .. versionadded:: 3.2 *maxtasksperchild* -- 2.47.3