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Code Issues Projects Releases Packages Wiki Activity Actions 8

GH-84559: Deprecate fork being the multiprocessing default. (#100618)

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This starts the process. Users who don't specify their own start method
and use the default on platforms where it is 'fork' will see a
DeprecationWarning upon multiprocessing.Pool() construction or upon
multiprocessing.Process.start() or concurrent.futures.ProcessPool use.

See the related issue and documentation within this change for details.
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Gregory P. Smith 2023-02-02 15:50:35 -08:00 • committed by GitHub
parent 618b7a8260
commit 0ca67e6313
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16 changed files with 284 additions and 63 deletions
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23
Lib/concurrent/futures/process.py
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@ -57,6 +57,7 @@ from functools import partial
import itertools
import sys
from traceback import format_exception
import warnings
_threads_wakeups = weakref.WeakKeyDictionary()
@ -616,9 +617,9 @@ class ProcessPoolExecutor(_base.Executor):
max_workers: The maximum number of processes that can be used to
execute the given calls. If None or not given then as many
worker processes will be created as the machine has processors.
mp_context: A multiprocessing context to launch the workers. This
object should provide SimpleQueue, Queue and Process. Useful
to allow specific multiprocessing start methods.
mp_context: A multiprocessing context to launch the workers created
using the multiprocessing.get_context('start method') API. This
object should provide SimpleQueue, Queue and Process.
initializer: A callable used to initialize worker processes.
initargs: A tuple of arguments to pass to the initializer.
max_tasks_per_child: The maximum number of tasks a worker process
@ -650,6 +651,22 @@ class ProcessPoolExecutor(_base.Executor):
mp_context = mp.get_context("spawn")
else:
mp_context = mp.get_context()
if (mp_context.get_start_method() == "fork" and
mp_context == mp.context._default_context._default_context):
warnings.warn(
"The default multiprocessing start method will change "
"away from 'fork' in Python >= 3.14, per GH-84559. "
"ProcessPoolExecutor uses multiprocessing. "
"If your application requires the 'fork' multiprocessing "
"start method, explicitly specify that by passing a "
"mp_context= parameter. "
"The safest start method is 'spawn'.",
category=mp.context.DefaultForkDeprecationWarning,
stacklevel=2,
)
# Avoid the equivalent warning from multiprocessing itself via
# a non-default fork context.
mp_context = mp.get_context("fork")
self._mp_context = mp_context
# https://github.com/python/cpython/issues/90622