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Commitd4c410f

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gh-84559: Remove the new multiprocessing warning, too disruptive. (#101551)
This reverts the core of#100618 while leaving relevant documentationimprovements and minor refactorings in place.
1 parentf6c53b8 commitd4c410f

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11 files changed

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11 files changed

+27
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‎Doc/library/concurrent.futures.rst‎

Lines changed: 8 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -281,18 +281,18 @@ to a :class:`ProcessPoolExecutor` will result in deadlock.
281281

282282
Added the *initializer* and *initargs* arguments.
283283

284+
..note::
285+
The default:mod:`multiprocessing` start method
286+
(see:ref:`multiprocessing-start-methods`) will change away from
287+
*fork* in Python 3.14. Code that requires *fork* be used for their
288+
:class:`ProcessPoolExecutor` should explicitly specify that by
289+
passing a ``mp_context=multiprocessing.get_context("fork")``
290+
parameter.
291+
284292
..versionchanged::3.11
285293
The *max_tasks_per_child* argument was added to allow users to
286294
control the lifetime of workers in the pool.
287295

288-
..versionchanged::3.12
289-
The implicit use of the:mod:`multiprocessing` *fork* start method as a
290-
platform default (see:ref:`multiprocessing-start-methods`) now raises a
291-
:exc:`DeprecationWarning`. The default will change in Python 3.14.
292-
Code that requires *fork* should explicitly specify that when creating
293-
their:class:`ProcessPoolExecutor` by passing a
294-
``mp_context=multiprocessing.get_context('fork')`` parameter.
295-
296296
.. _processpoolexecutor-example:
297297

298298
ProcessPoolExecutor Example

‎Doc/library/multiprocessing.rst‎

Lines changed: 6 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -126,6 +126,11 @@ to start a process. These *start methods* are
126126

127127
Available on POSIX systems. Currently the default on POSIX except macOS.
128128

129+
..note::
130+
The default start method will change away from *fork* in Python 3.14.
131+
Code that requires *fork* should explicitly specify that via
132+
:func:`get_context` or:func:`set_start_method`.
133+
129134
*forkserver*
130135
When the program starts and selects the *forkserver* start method,
131136
a server process is spawned. From then on, whenever a new process
@@ -138,11 +143,6 @@ to start a process. These *start methods* are
138143
Available on POSIX platforms which support passing file descriptors
139144
over Unix pipes such as Linux.
140145

141-
..versionchanged::3.12
142-
Implicit use of the *fork* start method as the default now raises a
143-
:exc:`DeprecationWarning`. Code that requires it should explicitly
144-
specify *fork* via:func:`get_context` or:func:`set_start_method`.
145-
The default will change away from *fork* in 3.14.
146146

147147
..versionchanged::3.8
148148

@@ -1107,6 +1107,7 @@ Miscellaneous
11071107
launched (before creating a:class:`Pool` or starting a:class:`Process`).
11081108

11091109
Only meaningful when using the ``'forkserver'`` start method.
1110+
See:ref:`multiprocessing-start-methods`.
11101111

11111112
..versionadded::3.4
11121113

‎Doc/whatsnew/3.12.rst‎

Lines changed: 7 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -440,12 +440,6 @@ Deprecated
440440
warning at compile time. This field will be removed in Python 3.14.
441441
(Contributed by Ramvikrams and Kumar Aditya in:gh:`101193`. PEP by Ken Jin.)
442442

443-
* Use of the implicit default ``'fork'`` start method for
444-
:mod:`multiprocessing` and:class:`concurrent.futures.ProcessPoolExecutor`
445-
now emits a:exc:`DeprecationWarning` on Linux and other non-macOS POSIX
446-
systems. Avoid this by explicitly specifying a start method.
447-
See:ref:`multiprocessing-start-methods`.
448-
449443
Pending Removal in Python 3.13
450444
------------------------------
451445

@@ -510,9 +504,13 @@ Pending Removal in Python 3.14
510504
* Testing the truth value of an:class:`xml.etree.ElementTree.Element`
511505
is deprecated and will raise an exception in Python 3.14.
512506

513-
* The default:mod:`multiprocessing` start method will change to one of either
514-
``'forkserver'`` or ``'spawn'`` on all platforms for which ``'fork'`` remains
515-
the default per:gh:`84559`.
507+
* The default:mod:`multiprocessing` start method will change to a safer one on
508+
Linux, BSDs, and other non-macOS POSIX platforms where ``'fork'`` is currently
509+
the default (:gh:`84559`). Adding a runtime warning about this was deemed too
510+
disruptive as the majority of code is not expected to care. Use the
511+
:func:`~multiprocessing.get_context` or
512+
:func:`~multiprocessing.set_start_method` APIs to explicitly specify when
513+
your code *requires* ``'fork'``. See:ref:`multiprocessing-start-methods`.
516514

517515
Pending Removal in Future Versions
518516
----------------------------------

‎Lib/concurrent/futures/process.py‎

Lines changed: 0 additions & 17 deletions
Original file line numberDiff line numberDiff line change
@@ -57,7 +57,6 @@
5757
importitertools
5858
importsys
5959
fromtracebackimportformat_exception
60-
importwarnings
6160

6261

6362
_threads_wakeups=weakref.WeakKeyDictionary()
@@ -651,22 +650,6 @@ def __init__(self, max_workers=None, mp_context=None,
651650
mp_context=mp.get_context("spawn")
652651
else:
653652
mp_context=mp.get_context()
654-
if (mp_context.get_start_method()=="fork"and
655-
mp_context==mp.context._default_context._default_context):
656-
warnings.warn(
657-
"The default multiprocessing start method will change "
658-
"away from 'fork' in Python >= 3.14, per GH-84559. "
659-
"ProcessPoolExecutor uses multiprocessing. "
660-
"If your application requires the 'fork' multiprocessing "
661-
"start method, explicitly specify that by passing a "
662-
"mp_context= parameter. "
663-
"The safest start method is 'spawn'.",
664-
category=mp.context.DefaultForkDeprecationWarning,
665-
stacklevel=2,
666-
)
667-
# Avoid the equivalent warning from multiprocessing itself via
668-
# a non-default fork context.
669-
mp_context=mp.get_context("fork")
670653
self._mp_context=mp_context
671654

672655
# https://github.com/python/cpython/issues/90622

‎Lib/multiprocessing/context.py‎

Lines changed: 1 addition & 27 deletions
Original file line numberDiff line numberDiff line change
@@ -23,9 +23,6 @@ class TimeoutError(ProcessError):
2323
classAuthenticationError(ProcessError):
2424
pass
2525

26-
classDefaultForkDeprecationWarning(DeprecationWarning):
27-
pass
28-
2926
#
3027
# Base type for contexts. Bound methods of an instance of this type are included in __all__ of __init__.py
3128
#
@@ -284,23 +281,6 @@ def _Popen(process_obj):
284281
from .popen_forkimportPopen
285282
returnPopen(process_obj)
286283

287-
_warn_package_prefixes= (os.path.dirname(__file__),)
288-
289-
class_DeprecatedForkProcess(ForkProcess):
290-
@classmethod
291-
def_Popen(cls,process_obj):
292-
importwarnings
293-
warnings.warn(
294-
"The default multiprocessing start method will change "
295-
"away from 'fork' in Python >= 3.14, per GH-84559. "
296-
"Use multiprocessing.get_context(X) or .set_start_method(X) to "
297-
"explicitly specify it when your application requires 'fork'. "
298-
"The safest start method is 'spawn'.",
299-
category=DefaultForkDeprecationWarning,
300-
skip_file_prefixes=_warn_package_prefixes,
301-
)
302-
returnsuper()._Popen(process_obj)
303-
304284
classSpawnProcess(process.BaseProcess):
305285
_start_method='spawn'
306286
@staticmethod
@@ -324,9 +304,6 @@ class ForkContext(BaseContext):
324304
_name='fork'
325305
Process=ForkProcess
326306

327-
class_DefaultForkContext(ForkContext):
328-
Process=_DeprecatedForkProcess
329-
330307
classSpawnContext(BaseContext):
331308
_name='spawn'
332309
Process=SpawnProcess
@@ -342,16 +319,13 @@ def _check_available(self):
342319
'fork':ForkContext(),
343320
'spawn':SpawnContext(),
344321
'forkserver':ForkServerContext(),
345-
# Remove None and _DefaultForkContext() when changing the default
346-
# in 3.14 for https://github.com/python/cpython/issues/84559.
347-
None:_DefaultForkContext(),
348322
}
349323
ifsys.platform=='darwin':
350324
# bpo-33725: running arbitrary code after fork() is no longer reliable
351325
# on macOS since macOS 10.14 (Mojave). Use spawn by default instead.
352326
_default_context=DefaultContext(_concrete_contexts['spawn'])
353327
else:
354-
_default_context=DefaultContext(_concrete_contexts[None])
328+
_default_context=DefaultContext(_concrete_contexts['fork'])
355329

356330
else:
357331

‎Lib/test/_test_multiprocessing.py‎

Lines changed: 2 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -4098,10 +4098,9 @@ def test_shared_memory_SharedMemoryServer_ignores_sigint(self):
40984098
deftest_shared_memory_SharedMemoryManager_reuses_resource_tracker(self):
40994099
# bpo-36867: test that a SharedMemoryManager uses the
41004100
# same resource_tracker process as its parent.
4101-
cmd=f'''if 1:
4101+
cmd='''if 1:
41024102
from multiprocessing.managers import SharedMemoryManager
4103-
from multiprocessing import set_start_method
4104-
set_start_method({multiprocessing.get_start_method()!r})
4103+
41054104
41064105
smm = SharedMemoryManager()
41074106
smm.start()

‎Lib/test/test_concurrent_futures.py‎

Lines changed: 0 additions & 19 deletions
Original file line numberDiff line numberDiff line change
@@ -18,7 +18,6 @@
1818
importthreading
1919
importtime
2020
importunittest
21-
importwarnings
2221
importweakref
2322
frompickleimportPicklingError
2423

@@ -572,24 +571,6 @@ def test_shutdown_no_wait(self):
572571
assertall([r==abs(v)forr,vinzip(res,range(-5,5))])
573572

574573

575-
@unittest.skipIf(mp.get_all_start_methods()[0]!="fork","non-fork default.")
576-
classProcessPoolExecutorDefaultForkWarning(unittest.TestCase):
577-
deftest_fork_default_warns(self):
578-
withself.assertWarns(mp.context.DefaultForkDeprecationWarning):
579-
withfutures.ProcessPoolExecutor(2):
580-
pass
581-
582-
deftest_explicit_fork_does_not_warn(self):
583-
withwarnings.catch_warnings(record=True)asws:
584-
warnings.simplefilter("ignore")
585-
warnings.filterwarnings(
586-
'always',category=mp.context.DefaultForkDeprecationWarning)
587-
ctx=mp.get_context("fork")# Non-default fork context.
588-
withfutures.ProcessPoolExecutor(2,mp_context=ctx):
589-
pass
590-
self.assertEqual(len(ws),0,msg=[str(x)forxinws])
591-
592-
593574
create_executor_tests(ProcessPoolShutdownTest,
594575
executor_mixins=(ProcessPoolForkMixin,
595576
ProcessPoolForkserverMixin,

‎Lib/test/test_logging.py‎

Lines changed: 2 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -4759,9 +4759,8 @@ def test_multiprocessing(self):
47594759
# In other processes, processName is correct when multiprocessing in imported,
47604760
# but it is (incorrectly) defaulted to 'MainProcess' otherwise (bpo-38762).
47614761
importmultiprocessing
4762-
mp=multiprocessing.get_context('spawn')
4763-
parent_conn,child_conn=mp.Pipe()
4764-
p=mp.Process(
4762+
parent_conn,child_conn=multiprocessing.Pipe()
4763+
p=multiprocessing.Process(
47654764
target=self._extract_logrecord_process_name,
47664765
args=(2,LOG_MULTI_PROCESSING,child_conn,)
47674766
)

‎Lib/test/test_multiprocessing_defaults.py‎

Lines changed: 0 additions & 85 deletions
This file was deleted.

‎Lib/test/test_re.py‎

Lines changed: 1 addition & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -2431,8 +2431,7 @@ def test_regression_gh94675(self):
24312431
input_js='''a(function() {
24322432
///////////////////////////////////////////////////////////////////
24332433
});'''
2434-
mp=multiprocessing.get_context('spawn')
2435-
p=mp.Process(target=pattern.sub,args=('',input_js))
2434+
p=multiprocessing.Process(target=pattern.sub,args=('',input_js))
24362435
p.start()
24372436
p.join(SHORT_TIMEOUT)
24382437
try:

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