[Python-checkins] bpo-17140: Document multiprocessing's ThreadPool (GH-23812)
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Fri Dec 18 08:27:07 EST 2020
author: Miss Islington (bot) <31488909+miss-islington at users.noreply.github.com>
committer: miss-islington <31488909+miss-islington at users.noreply.github.com>
bpo-17140: Document multiprocessing's ThreadPool (GH-23812)
Up until now, the `multiprocessing.pool.ThreadPool` class has gone
undocumented, despite being a public class in multiprocessing that is
included in `multiprocessing.pool.__all__`.
(cherry picked from commit 84ebcf271a2cc8bfd1762acb279502b8b6ef236e)
Co-authored-by: Matt Wozniski <mwozniski at bloomberg.net>
diff --git a/Doc/library/multiprocessing.rst b/Doc/library/multiprocessing.rst
index ab84d39ed0516..352f48f513df9 100644
@@ -2661,6 +2661,46 @@ The :mod:`multiprocessing.dummy` module
:mod:`multiprocessing.dummy` replicates the API of :mod:`multiprocessing` but is
no more than a wrapper around the :mod:`threading` module.
+.. currentmodule:: multiprocessing.pool
+In particular, the ``Pool`` function provided by :mod:`multiprocessing.dummy`
+returns an instance of :class:`ThreadPool`, which is a subclass of
+:class:`Pool` that supports all the same method calls but uses a pool of
+worker threads rather than worker processes.
+.. class:: ThreadPool([processes[, initializer[, initargs]]])
+ A thread pool object which controls a pool of worker threads to which jobs
+ can be submitted. :class:`ThreadPool` instances are fully interface
+ compatible with :class:`Pool` instances, and their resources must also be
+ properly managed, either by using the pool as a context manager or by
+ calling :meth:`~multiprocessing.pool.Pool.close` and
+ :meth:`~multiprocessing.pool.Pool.terminate` manually.
+ *processes* is the number of worker threads to use. If *processes* is
+ ``None`` then the number returned by :func:`os.cpu_count` is used.
+ If *initializer* is not ``None`` then each worker process will call
+ ``initializer(*initargs)`` when it starts.
+ Unlike :class:`Pool`, *maxtasksperchild* and *context* cannot be provided.
+ .. note::
+ A :class:`ThreadPool` shares the same interface as :class:`Pool`, which
+ is designed around a pool of processes and predates the introduction of
+ the :class:`concurrent.futures` module. As such, it inherits some
+ operations that don't make sense for a pool backed by threads, and it
+ has its own type for representing the status of asynchronous jobs,
+ :class:`AsyncResult`, that is not understood by any other libraries.
+ Users should generally prefer to use
+ :class:`concurrent.futures.ThreadPoolExecutor`, which has a simpler
+ interface that was designed around threads from the start, and which
+ returns :class:`concurrent.futures.Future` instances that are
+ compatible with many other libraries, including :mod:`asyncio`.
diff --git a/Misc/NEWS.d/next/Documentation/2020-12-16-21-06-16.bpo-17140.1leSEg.rst b/Misc/NEWS.d/next/Documentation/2020-12-16-21-06-16.bpo-17140.1leSEg.rst
new file mode 100644
@@ -0,0 +1 @@
+Add documentation for the :class:`multiprocessing.pool.ThreadPool` class.
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