then :exc:`ValueError` will be raised. If *max_workers* is ``None``, then
the default chosen will be at most ``61``, even if more processors are
available.
- *mp_context* can be a multiprocessing context or None. It will be used to
- launch the workers. If *mp_context* is ``None`` or not given, the default
- multiprocessing context is used.
+ *mp_context* can be a :mod:`multiprocessing` context or ``None``. It will be
+ used to launch the workers. If *mp_context* is ``None`` or not given, the
+ default :mod:`multiprocessing` context is used.
+ See :ref:`multiprocessing-start-methods`.
*initializer* is an optional callable that is called at the start of
each worker process; *initargs* is a tuple of arguments passed to the
The *max_tasks_per_child* argument was added to allow users to
control the lifetime of workers in the pool.
+ .. versionchanged:: 3.12
+ The implicit use of the :mod:`multiprocessing` *fork* start method as a
+ platform default (see :ref:`multiprocessing-start-methods`) now raises a
+ :exc:`DeprecationWarning`. The default will change in Python 3.14.
+ Code that requires *fork* should explicitly specify that when creating
+ their :class:`ProcessPoolExecutor` by passing a
+ ``mp_context=multiprocessing.get_context('fork')`` parameter.
.. _processpoolexecutor-example:
:term:`Global Interpreter Lock <global interpreter lock>` by using
subprocesses instead of threads. Due
to this, the :mod:`multiprocessing` module allows the programmer to fully
-leverage multiple processors on a given machine. It runs on both Unix and
+leverage multiple processors on a given machine. It runs on both POSIX and
Windows.
The :mod:`multiprocessing` module also introduces APIs which do not have
+.. _multiprocessing-start-methods:
+
Contexts and start methods
~~~~~~~~~~~~~~~~~~~~~~~~~~
-.. _multiprocessing-start-methods:
-
Depending on the platform, :mod:`multiprocessing` supports three ways
to start a process. These *start methods* are
will not be inherited. Starting a process using this method is
rather slow compared to using *fork* or *forkserver*.
- Available on Unix and Windows. The default on Windows and macOS.
+ Available on POSIX and Windows platforms. The default on Windows and macOS.
*fork*
The parent process uses :func:`os.fork` to fork the Python
inherited by the child process. Note that safely forking a
multithreaded process is problematic.
- Available on Unix only. The default on Unix.
+ Available on POSIX systems. Currently the default on POSIX except macOS.
*forkserver*
When the program starts and selects the *forkserver* start method,
- a server process is started. From then on, whenever a new process
+ a server process is spawned. From then on, whenever a new process
is needed, the parent process connects to the server and requests
- that it fork a new process. The fork server process is single
- threaded so it is safe for it to use :func:`os.fork`. No
- unnecessary resources are inherited.
+ that it fork a new process. The fork server process is single threaded
+ unless system libraries or preloaded imports spawn threads as a
+ side-effect so it is generally safe for it to use :func:`os.fork`.
+ No unnecessary resources are inherited.
- Available on Unix platforms which support passing file descriptors
- over Unix pipes.
+ Available on POSIX platforms which support passing file descriptors
+ over Unix pipes such as Linux.
+
+.. versionchanged:: 3.12
+ Implicit use of the *fork* start method as the default now raises a
+ :exc:`DeprecationWarning`. Code that requires it should explicitly
+ specify *fork* via :func:`get_context` or :func:`set_start_method`.
+ The default will change away from *fork* in 3.14.
.. versionchanged:: 3.8
On macOS, the *spawn* start method is now the default. The *fork* start
method should be considered unsafe as it can lead to crashes of the
- subprocess. See :issue:`33725`.
+ subprocess as macOS system libraries may start threads. See :issue:`33725`.
.. versionchanged:: 3.4
- *spawn* added on all Unix platforms, and *forkserver* added for
- some Unix platforms.
+ *spawn* added on all POSIX platforms, and *forkserver* added for
+ some POSIX platforms.
Child processes no longer inherit all of the parents inheritable
handles on Windows.
-On Unix using the *spawn* or *forkserver* start methods will also
+On POSIX using the *spawn* or *forkserver* start methods will also
start a *resource tracker* process which tracks the unlinked named
system resources (such as named semaphores or
:class:`~multiprocessing.shared_memory.SharedMemory` objects) created
.. warning::
- The ``'spawn'`` and ``'forkserver'`` start methods cannot currently
+ The ``'spawn'`` and ``'forkserver'`` start methods generally cannot
be used with "frozen" executables (i.e., binaries produced by
- packages like **PyInstaller** and **cx_Freeze**) on Unix.
- The ``'fork'`` start method does work.
+ packages like **PyInstaller** and **cx_Freeze**) on POSIX systems.
+ The ``'fork'`` start method may work if code does not use threads.
Exchanging objects between processes
calling :meth:`join()` is simpler.
On Windows, this is an OS handle usable with the ``WaitForSingleObject``
- and ``WaitForMultipleObjects`` family of API calls. On Unix, this is
+ and ``WaitForMultipleObjects`` family of API calls. On POSIX, this is
a file descriptor usable with primitives from the :mod:`select` module.
.. versionadded:: 3.3
.. method:: terminate()
- Terminate the process. On Unix this is done using the ``SIGTERM`` signal;
+ Terminate the process. On POSIX this is done using the ``SIGTERM`` signal;
on Windows :c:func:`TerminateProcess` is used. Note that exit handlers and
finally clauses, etc., will not be executed.
.. method:: kill()
- Same as :meth:`terminate()` but using the ``SIGKILL`` signal on Unix.
+ Same as :meth:`terminate()` but using the ``SIGKILL`` signal on POSIX.
.. versionadded:: 3.7
.. doctest::
>>> import multiprocessing, time, signal
- >>> p = multiprocessing.Process(target=time.sleep, args=(1000,))
+ >>> mp_context = multiprocessing.get_context('spawn')
+ >>> p = mp_context.Process(target=time.sleep, args=(1000,))
>>> print(p, p.is_alive())
- <Process ... initial> False
+ <...Process ... initial> False
>>> p.start()
>>> print(p, p.is_alive())
- <Process ... started> True
+ <...Process ... started> True
>>> p.terminate()
>>> time.sleep(0.1)
>>> print(p, p.is_alive())
- <Process ... stopped exitcode=-SIGTERM> False
+ <...Process ... stopped exitcode=-SIGTERM> False
>>> p.exitcode == -signal.SIGTERM
True
Return the approximate size of the queue. Because of
multithreading/multiprocessing semantics, this number is not reliable.
- Note that this may raise :exc:`NotImplementedError` on Unix platforms like
+ Note that this may raise :exc:`NotImplementedError` on platforms like
macOS where ``sem_getvalue()`` is not implemented.
.. method:: empty()
Returns a list of the supported start methods, the first of which
is the default. The possible start methods are ``'fork'``,
- ``'spawn'`` and ``'forkserver'``. On Windows only ``'spawn'`` is
- available. On Unix ``'fork'`` and ``'spawn'`` are always
- supported, with ``'fork'`` being the default.
+ ``'spawn'`` and ``'forkserver'``. Not all platforms support all
+ methods. See :ref:`multiprocessing-start-methods`.
.. versionadded:: 3.4
If *method* is ``None`` then the default context is returned.
Otherwise *method* should be ``'fork'``, ``'spawn'``,
``'forkserver'``. :exc:`ValueError` is raised if the specified
- start method is not available.
+ start method is not available. See :ref:`multiprocessing-start-methods`.
.. versionadded:: 3.4
is true then ``None`` is returned.
The return value can be ``'fork'``, ``'spawn'``, ``'forkserver'``
- or ``None``. ``'fork'`` is the default on Unix, while ``'spawn'`` is
- the default on Windows and macOS.
+ or ``None``. See :ref:`multiprocessing-start-methods`.
.. versionchanged:: 3.8
before they can create child processes.
.. versionchanged:: 3.4
- Now supported on Unix when the ``'spawn'`` start method is used.
+ Now supported on POSIX when the ``'spawn'`` start method is used.
.. versionchanged:: 3.11
Accepts a :term:`path-like object`.
+.. function:: set_forkserver_preload(module_names)
+
+ Set a list of module names for the forkserver main process to attempt to
+ import so that their already imported state is inherited by forked
+ processes. Any :exc:`ImportError` when doing so is silently ignored.
+ This can be used as a performance enhancement to avoid repeated work
+ in every process.
+
+ For this to work, it must be called before the forkserver process has been
+ launched (before creating a :class:`Pool` or starting a :class:`Process`).
+
+ Only meaningful when using the ``'forkserver'`` start method.
+
+ .. versionadded:: 3.4
+
.. function:: set_start_method(method, force=False)
Set the method which should be used to start child processes.
protected inside the ``if __name__ == '__main__'`` clause of the
main module.
+ See :ref:`multiprocessing-start-methods`.
+
.. versionadded:: 3.4
.. note::
.. doctest::
- >>> manager = multiprocessing.Manager()
+ >>> mp_context = multiprocessing.get_context('spawn')
+ >>> manager = mp_context.Manager()
>>> Global = manager.Namespace()
>>> Global.x = 10
>>> Global.y = 'hello'
.. doctest::
- >>> from multiprocessing import Manager
- >>> manager = Manager()
+ >>> mp_context = multiprocessing.get_context('spawn')
+ >>> manager = mp_context.Manager()
>>> l = manager.list([i*i for i in range(10)])
>>> print(l)
[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
*timeout* is ``None`` then it will block for an unlimited period.
A negative timeout is equivalent to a zero timeout.
- For both Unix and Windows, an object can appear in *object_list* if
+ For both POSIX and Windows, an object can appear in *object_list* if
it is
* a readable :class:`~multiprocessing.connection.Connection` object;
A connection or socket object is ready when there is data available
to be read from it, or the other end has been closed.
- **Unix**: ``wait(object_list, timeout)`` almost equivalent
+ **POSIX**: ``wait(object_list, timeout)`` almost equivalent
``select.select(object_list, [], [], timeout)``. The difference is
that, if :func:`select.select` is interrupted by a signal, it can
raise :exc:`OSError` with an error number of ``EINTR``, whereas
Joining zombie processes
- On Unix when a process finishes but has not been joined it becomes a zombie.
+ On POSIX when a process finishes but has not been joined it becomes a zombie.
There should never be very many because each time a new process starts (or
:func:`~multiprocessing.active_children` is called) all completed processes
which have not yet been joined will be joined. Also calling a finished
Explicitly pass resources to child processes
- On Unix using the *fork* start method, a child process can make
+ On POSIX using the *fork* start method, a child process can make
use of a shared resource created in a parent process using a
global resource. However, it is better to pass the object as an
argument to the constructor for the child process.
warning at compile time. This field will be removed in Python 3.14.
(Contributed by Ramvikrams and Kumar Aditya in :gh:`101193`. PEP by Ken Jin.)
+* Use of the implicit default ``'fork'`` start method for
+ :mod:`multiprocessing` and :class:`concurrent.futures.ProcessPoolExecutor`
+ now emits a :exc:`DeprecationWarning` on Linux and other non-macOS POSIX
+ systems. Avoid this by explicitly specifying a start method.
+ See :ref:`multiprocessing-start-methods`.
Pending Removal in Python 3.13
------------------------------
* Testing the truth value of an :class:`xml.etree.ElementTree.Element`
is deprecated and will raise an exception in Python 3.14.
+* The default :mod:`multiprocessing` start method will change to one of either
+ ``'forkserver'`` or ``'spawn'`` on all platforms for which ``'fork'`` remains
+ the default per :gh:`84559`.
Pending Removal in Future Versions
----------------------------------
files = _walk_dir(dir, quiet=quiet, maxlevels=maxlevels)
success = True
if workers != 1 and ProcessPoolExecutor is not None:
+ import multiprocessing
+ if multiprocessing.get_start_method() == 'fork':
+ mp_context = multiprocessing.get_context('forkserver')
+ else:
+ mp_context = None
# If workers == 0, let ProcessPoolExecutor choose
workers = workers or None
- with ProcessPoolExecutor(max_workers=workers) as executor:
+ with ProcessPoolExecutor(max_workers=workers,
+ mp_context=mp_context) as executor:
results = executor.map(partial(compile_file,
ddir=ddir, force=force,
rx=rx, quiet=quiet,
import itertools
import sys
from traceback import format_exception
+import warnings
_threads_wakeups = weakref.WeakKeyDictionary()
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
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
class AuthenticationError(ProcessError):
pass
+class DefaultForkDeprecationWarning(DeprecationWarning):
+ pass
+
#
# Base type for contexts. Bound methods of an instance of this type are included in __all__ of __init__.py
#
return self._actual_context._name
def get_all_start_methods(self):
+ """Returns a list of the supported start methods, default first."""
if sys.platform == 'win32':
return ['spawn']
else:
from .popen_fork import Popen
return Popen(process_obj)
+ _warn_package_prefixes = (os.path.dirname(__file__),)
+
+ class _DeprecatedForkProcess(ForkProcess):
+ @classmethod
+ def _Popen(cls, process_obj):
+ import warnings
+ warnings.warn(
+ "The default multiprocessing start method will change "
+ "away from 'fork' in Python >= 3.14, per GH-84559. "
+ "Use multiprocessing.get_context(X) or .set_start_method(X) to "
+ "explicitly specify it when your application requires 'fork'. "
+ "The safest start method is 'spawn'.",
+ category=DefaultForkDeprecationWarning,
+ skip_file_prefixes=_warn_package_prefixes,
+ )
+ return super()._Popen(process_obj)
+
class SpawnProcess(process.BaseProcess):
_start_method = 'spawn'
@staticmethod
_name = 'fork'
Process = ForkProcess
+ class _DefaultForkContext(ForkContext):
+ Process = _DeprecatedForkProcess
+
class SpawnContext(BaseContext):
_name = 'spawn'
Process = SpawnProcess
'fork': ForkContext(),
'spawn': SpawnContext(),
'forkserver': ForkServerContext(),
+ # Remove None and _DefaultForkContext() when changing the default
+ # in 3.14 for https://github.com/python/cpython/issues/84559.
+ None: _DefaultForkContext(),
}
if sys.platform == 'darwin':
# bpo-33725: running arbitrary code after fork() is no longer reliable
# on macOS since macOS 10.14 (Mojave). Use spawn by default instead.
_default_context = DefaultContext(_concrete_contexts['spawn'])
else:
- _default_context = DefaultContext(_concrete_contexts['fork'])
+ _default_context = DefaultContext(_concrete_contexts[None])
else:
def test_shared_memory_SharedMemoryManager_reuses_resource_tracker(self):
# bpo-36867: test that a SharedMemoryManager uses the
# same resource_tracker process as its parent.
- cmd = '''if 1:
+ cmd = f'''if 1:
from multiprocessing.managers import SharedMemoryManager
-
+ from multiprocessing import set_start_method
+ set_start_method({multiprocessing.get_start_method()!r})
smm = SharedMemoryManager()
smm.start()
conn.send(tuple(sys.flags))
@classmethod
- def run_in_child(cls):
+ def run_in_child(cls, start_method):
import json
- r, w = multiprocessing.Pipe(duplex=False)
- p = multiprocessing.Process(target=cls.run_in_grandchild, args=(w,))
- p.start()
+ mp = multiprocessing.get_context(start_method)
+ r, w = mp.Pipe(duplex=False)
+ p = mp.Process(target=cls.run_in_grandchild, args=(w,))
+ with warnings.catch_warnings(category=DeprecationWarning):
+ p.start()
grandchild_flags = r.recv()
p.join()
r.close()
def test_flags(self):
import json
# start child process using unusual flags
- prog = ('from test._test_multiprocessing import TestFlags; ' +
- 'TestFlags.run_in_child()')
+ prog = (
+ 'from test._test_multiprocessing import TestFlags; '
+ f'TestFlags.run_in_child({multiprocessing.get_start_method()!r})'
+ )
data = subprocess.check_output(
[sys.executable, '-E', '-S', '-O', '-c', prog])
child_flags, grandchild_flags = json.loads(data.decode('ascii'))
def main():
+ multiprocessing.set_start_method('spawn')
test_pool = multiprocessing.Process(target=test_func)
test_pool.start()
test_pool.join()
import concurrent.futures
import functools
import io
+import multiprocessing
import os
import platform
import re
support.skip_if_broken_multiprocessing_synchronize()
async def main():
- pool = concurrent.futures.ProcessPoolExecutor()
+ if multiprocessing.get_start_method() == 'fork':
+ # Avoid 'fork' DeprecationWarning.
+ mp_context = multiprocessing.get_context('forkserver')
+ else:
+ mp_context = None
+ pool = concurrent.futures.ProcessPoolExecutor(
+ mp_context=mp_context)
result = await self.loop.run_in_executor(
pool, _test_get_event_loop_new_process__sub_proc)
pool.shutdown()
import threading
import time
import unittest
+import warnings
import weakref
from pickle import PicklingError
assert all([r == abs(v) for r, v in zip(res, range(-5, 5))])
+@unittest.skipIf(mp.get_all_start_methods()[0] != "fork", "non-fork default.")
+class ProcessPoolExecutorDefaultForkWarning(unittest.TestCase):
+ def test_fork_default_warns(self):
+ with self.assertWarns(mp.context.DefaultForkDeprecationWarning):
+ with futures.ProcessPoolExecutor(2):
+ pass
+
+ def test_explicit_fork_does_not_warn(self):
+ with warnings.catch_warnings(record=True) as ws:
+ warnings.simplefilter("ignore")
+ warnings.filterwarnings(
+ 'always', category=mp.context.DefaultForkDeprecationWarning)
+ ctx = mp.get_context("fork") # Non-default fork context.
+ with futures.ProcessPoolExecutor(2, mp_context=ctx):
+ pass
+ self.assertEqual(len(ws), 0, msg=[str(x) for x in ws])
+
+
create_executor_tests(ProcessPoolShutdownTest,
executor_mixins=(ProcessPoolForkMixin,
ProcessPoolForkserverMixin,
"""Test program for the fcntl C module.
"""
+import multiprocessing
import platform
import os
import struct
import sys
import unittest
-from multiprocessing import Process
from test.support import verbose, cpython_only
from test.support.import_helper import import_module
from test.support.os_helper import TESTFN, unlink
self.f = open(TESTFN, 'wb+')
cmd = fcntl.LOCK_EX | fcntl.LOCK_NB
fcntl.lockf(self.f, cmd)
- p = Process(target=try_lockf_on_other_process_fail, args=(TESTFN, cmd))
+ mp = multiprocessing.get_context('spawn')
+ p = mp.Process(target=try_lockf_on_other_process_fail, args=(TESTFN, cmd))
p.start()
p.join()
fcntl.lockf(self.f, fcntl.LOCK_UN)
self.f = open(TESTFN, 'wb+')
cmd = fcntl.LOCK_SH | fcntl.LOCK_NB
fcntl.lockf(self.f, cmd)
- p = Process(target=try_lockf_on_other_process, args=(TESTFN, cmd))
+ mp = multiprocessing.get_context('spawn')
+ p = mp.Process(target=try_lockf_on_other_process, args=(TESTFN, cmd))
p.start()
p.join()
fcntl.lockf(self.f, fcntl.LOCK_UN)
# In other processes, processName is correct when multiprocessing in imported,
# but it is (incorrectly) defaulted to 'MainProcess' otherwise (bpo-38762).
import multiprocessing
- parent_conn, child_conn = multiprocessing.Pipe()
- p = multiprocessing.Process(
+ mp = multiprocessing.get_context('spawn')
+ parent_conn, child_conn = mp.Pipe()
+ p = mp.Process(
target=self._extract_logrecord_process_name,
args=(2, LOG_MULTI_PROCESSING, child_conn,)
)
--- /dev/null
+"""Test default behavior of multiprocessing."""
+
+from inspect import currentframe, getframeinfo
+import multiprocessing
+from multiprocessing.context import DefaultForkDeprecationWarning
+import sys
+from test.support import threading_helper
+import unittest
+import warnings
+
+
+def do_nothing():
+ pass
+
+
+# Process has the same API as Thread so this helper works.
+join_process = threading_helper.join_thread
+
+
+class DefaultWarningsTest(unittest.TestCase):
+
+ @unittest.skipIf(sys.platform in ('win32', 'darwin'),
+ 'The default is not "fork" on Windows or macOS.')
+ def setUp(self):
+ self.assertEqual(multiprocessing.get_start_method(), 'fork')
+ self.assertIsInstance(multiprocessing.get_context(),
+ multiprocessing.context._DefaultForkContext)
+
+ def test_default_fork_start_method_warning_process(self):
+ with warnings.catch_warnings(record=True) as ws:
+ warnings.simplefilter('ignore')
+ warnings.filterwarnings('always', category=DefaultForkDeprecationWarning)
+ process = multiprocessing.Process(target=do_nothing)
+ process.start() # warning should point here.
+ join_process(process)
+ self.assertIsInstance(ws[0].message, DefaultForkDeprecationWarning)
+ self.assertIn(__file__, ws[0].filename)
+ self.assertEqual(getframeinfo(currentframe()).lineno-4, ws[0].lineno)
+ self.assertIn("'fork'", str(ws[0].message))
+ self.assertIn("get_context", str(ws[0].message))
+ self.assertEqual(len(ws), 1, msg=[str(x) for x in ws])
+
+ def test_default_fork_start_method_warning_pool(self):
+ with warnings.catch_warnings(record=True) as ws:
+ warnings.simplefilter('ignore')
+ warnings.filterwarnings('always', category=DefaultForkDeprecationWarning)
+ pool = multiprocessing.Pool(1) # warning should point here.
+ pool.terminate()
+ pool.join()
+ self.assertIsInstance(ws[0].message, DefaultForkDeprecationWarning)
+ self.assertIn(__file__, ws[0].filename)
+ self.assertEqual(getframeinfo(currentframe()).lineno-5, ws[0].lineno)
+ self.assertIn("'fork'", str(ws[0].message))
+ self.assertIn("get_context", str(ws[0].message))
+ self.assertEqual(len(ws), 1, msg=[str(x) for x in ws])
+
+ def test_default_fork_start_method_warning_manager(self):
+ with warnings.catch_warnings(record=True) as ws:
+ warnings.simplefilter('ignore')
+ warnings.filterwarnings('always', category=DefaultForkDeprecationWarning)
+ manager = multiprocessing.Manager() # warning should point here.
+ manager.shutdown()
+ self.assertIsInstance(ws[0].message, DefaultForkDeprecationWarning)
+ self.assertIn(__file__, ws[0].filename)
+ self.assertEqual(getframeinfo(currentframe()).lineno-4, ws[0].lineno)
+ self.assertIn("'fork'", str(ws[0].message))
+ self.assertIn("get_context", str(ws[0].message))
+ self.assertEqual(len(ws), 1, msg=[str(x) for x in ws])
+
+ def test_no_mp_warning_when_using_explicit_fork_context(self):
+ with warnings.catch_warnings(record=True) as ws:
+ warnings.simplefilter('ignore')
+ warnings.filterwarnings('always', category=DefaultForkDeprecationWarning)
+ fork_mp = multiprocessing.get_context('fork')
+ pool = fork_mp.Pool(1)
+ pool.terminate()
+ pool.join()
+ self.assertEqual(len(ws), 0, msg=[str(x) for x in ws])
+
+
+if __name__ == '__main__':
+ unittest.main()
def test_multiprocessing_exceptions(self):
module = import_helper.import_module('multiprocessing.context')
for name, exc in get_exceptions(module):
+ if issubclass(exc, Warning):
+ continue
with self.subTest(name):
self.assertEqual(reverse_mapping('multiprocessing.context', name),
('multiprocessing', name))
input_js = '''a(function() {
///////////////////////////////////////////////////////////////////
});'''
- p = multiprocessing.Process(target=pattern.sub, args=('', input_js))
+ mp = multiprocessing.get_context('spawn')
+ p = mp.Process(target=pattern.sub, args=('', input_js))
p.start()
p.join(SHORT_TIMEOUT)
try:
--- /dev/null
+The :mod:`multiprocessing` module and
+:class:`concurrent.futures.ProcessPoolExecutor` will emit a
+:exc:`DeprecationWarning` on Linux and other non-macOS POSIX systems when
+the default multiprocessing start method of ``'fork'`` is used implicitly
+rather than being explicitly specified through a
+:func:`multiprocessing.get_context` context.
+
+This is in preparation for default start method to change in Python 3.14 to
+a default that is safe for multithreaded applications.
+
+Windows and macOS are unaffected as their default start method is ``spawn``.
projects / thirdparty / Python / cpython.git / commitdiff
