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[3.7] bpo-38501: Add a warning section to multiprocessing.Pool docs about resource managing (GH-19466) #19468

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Apr 11, 2020
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[3.7] bpo-38501: Add a warning section to multiprocessing.Pool docs about resource managing (GH-19466) #19468

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13 changes: 12 additions & 1 deletion Doc/library/multiprocessing.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -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:
Expand Down Expand Up @@ -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*

Expand Down