diff options
| -rw-r--r-- | Doc/library/concurrent.futures.rst | 14 | ||||
| -rw-r--r-- | Doc/library/multiprocessing.rst | 104 | ||||
| -rw-r--r-- | Doc/whatsnew/3.12.rst | 8 | ||||
| -rw-r--r-- | Lib/compileall.py | 8 | ||||
| -rw-r--r-- | Lib/concurrent/futures/process.py | 23 | ||||
| -rw-r--r-- | Lib/multiprocessing/context.py | 29 | ||||
| -rw-r--r-- | Lib/test/_test_multiprocessing.py | 21 | ||||
| -rw-r--r-- | Lib/test/_test_venv_multiprocessing.py | 1 | ||||
| -rw-r--r-- | Lib/test/test_asyncio/test_events.py | 9 | ||||
| -rw-r--r-- | Lib/test/test_concurrent_futures.py | 19 | ||||
| -rw-r--r-- | Lib/test/test_fcntl.py | 8 | ||||
| -rw-r--r-- | Lib/test/test_logging.py | 5 | ||||
| -rw-r--r-- | Lib/test/test_multiprocessing_defaults.py | 82 | ||||
| -rw-r--r-- | Lib/test/test_pickle.py | 2 | ||||
| -rw-r--r-- | Lib/test/test_re.py | 3 | ||||
| -rw-r--r-- | Misc/NEWS.d/next/Library/2023-01-01-01-19-33.gh-issue-84559.zEjsEJ.rst | 11 |
16 files changed, 284 insertions, 63 deletions
diff --git a/Doc/library/concurrent.futures.rst b/Doc/library/concurrent.futures.rst index 8106cc2..10cffda 100644 --- a/Doc/library/concurrent.futures.rst +++ b/Doc/library/concurrent.futures.rst @@ -250,9 +250,10 @@ to a :class:`ProcessPoolExecutor` will result in deadlock. 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 @@ -284,6 +285,13 @@ to a :class:`ProcessPoolExecutor` will result in deadlock. 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: diff --git a/Doc/library/multiprocessing.rst b/Doc/library/multiprocessing.rst index b5ceeb7..c60b229 100644 --- a/Doc/library/multiprocessing.rst +++ b/Doc/library/multiprocessing.rst @@ -19,7 +19,7 @@ offers both local and remote concurrency, effectively side-stepping the :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 @@ -99,11 +99,11 @@ necessary, see :ref:`multiprocessing-programming`. +.. _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 @@ -115,7 +115,7 @@ 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 @@ -124,32 +124,39 @@ to start a process. These *start methods* are 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 @@ -211,10 +218,10 @@ library user. .. 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 @@ -629,14 +636,14 @@ The :mod:`multiprocessing` package mostly replicates the API of the 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. @@ -653,7 +660,7 @@ The :mod:`multiprocessing` package mostly replicates the API of the .. 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 @@ -676,16 +683,17 @@ The :mod:`multiprocessing` package mostly replicates the API of the .. 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 @@ -815,7 +823,7 @@ For an example of the usage of queues for interprocess communication see 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() @@ -1034,9 +1042,8 @@ Miscellaneous 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 @@ -1048,7 +1055,7 @@ Miscellaneous 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 @@ -1062,8 +1069,7 @@ Miscellaneous 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 @@ -1084,11 +1090,26 @@ Miscellaneous 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. @@ -1102,6 +1123,8 @@ Miscellaneous protected inside the ``if __name__ == '__main__'`` clause of the main module. + See :ref:`multiprocessing-start-methods`. + .. versionadded:: 3.4 .. note:: @@ -1906,7 +1929,8 @@ their parent process exits. The manager classes are defined in the .. doctest:: - >>> manager = multiprocessing.Manager() + >>> mp_context = multiprocessing.get_context('spawn') + >>> manager = mp_context.Manager() >>> Global = manager.Namespace() >>> Global.x = 10 >>> Global.y = 'hello' @@ -2018,8 +2042,8 @@ the proxy). In this way, a proxy can be used just like its referent can: .. 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] @@ -2520,7 +2544,7 @@ multiple connections at the same time. *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; @@ -2531,7 +2555,7 @@ multiple connections at the same time. 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 @@ -2803,7 +2827,7 @@ Thread safety of proxies 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 @@ -2866,7 +2890,7 @@ Joining processes that use queues 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. diff --git a/Doc/whatsnew/3.12.rst b/Doc/whatsnew/3.12.rst index a071159..e675fad 100644 --- a/Doc/whatsnew/3.12.rst +++ b/Doc/whatsnew/3.12.rst @@ -440,6 +440,11 @@ Deprecated 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 ------------------------------ @@ -505,6 +510,9 @@ Pending Removal in Python 3.14 * 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 ---------------------------------- diff --git a/Lib/compileall.py b/Lib/compileall.py index a388931..d394156 100644 --- a/Lib/compileall.py +++ b/Lib/compileall.py @@ -97,9 +97,15 @@ def compile_dir(dir, maxlevels=None, ddir=None, force=False, 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, diff --git a/Lib/concurrent/futures/process.py b/Lib/concurrent/futures/process.py index 7e2f5fa..257dd02 100644 --- a/Lib/concurrent/futures/process.py +++ b/Lib/concurrent/futures/process.py @@ -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 diff --git a/Lib/multiprocessing/context.py b/Lib/multiprocessing/context.py index b1960ea..010a920 100644 --- a/Lib/multiprocessing/context.py +++ b/Lib/multiprocessing/context.py @@ -23,6 +23,9 @@ class TimeoutError(ProcessError): 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 # @@ -258,6 +261,7 @@ class DefaultContext(BaseContext): 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: @@ -280,6 +284,23 @@ if sys.platform != 'win32': 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 @@ -303,6 +324,9 @@ if sys.platform != 'win32': _name = 'fork' Process = ForkProcess + class _DefaultForkContext(ForkContext): + Process = _DeprecatedForkProcess + class SpawnContext(BaseContext): _name = 'spawn' Process = SpawnProcess @@ -318,13 +342,16 @@ if sys.platform != 'win32': '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: diff --git a/Lib/test/_test_multiprocessing.py b/Lib/test/_test_multiprocessing.py index 2fa75eb..e4a60a4 100644 --- a/Lib/test/_test_multiprocessing.py +++ b/Lib/test/_test_multiprocessing.py @@ -4098,9 +4098,10 @@ class _TestSharedMemory(BaseTestCase): 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() @@ -4967,11 +4968,13 @@ class TestFlags(unittest.TestCase): 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() @@ -4982,8 +4985,10 @@ class TestFlags(unittest.TestCase): 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')) diff --git a/Lib/test/_test_venv_multiprocessing.py b/Lib/test/_test_venv_multiprocessing.py index af72e91..044a0c6 100644 --- a/Lib/test/_test_venv_multiprocessing.py +++ b/Lib/test/_test_venv_multiprocessing.py @@ -30,6 +30,7 @@ def test_func(): def main(): + multiprocessing.set_start_method('spawn') test_pool = multiprocessing.Process(target=test_func) test_pool.start() test_pool.join() diff --git a/Lib/test/test_asyncio/test_events.py b/Lib/test/test_asyncio/test_events.py index 214544b..b906905 100644 --- a/Lib/test/test_asyncio/test_events.py +++ b/Lib/test/test_asyncio/test_events.py @@ -4,6 +4,7 @@ import collections.abc import concurrent.futures import functools import io +import multiprocessing import os import platform import re @@ -2762,7 +2763,13 @@ class GetEventLoopTestsMixin: 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() diff --git a/Lib/test/test_concurrent_futures.py b/Lib/test/test_concurrent_futures.py index b3520ae..4493cd3 100644 --- a/Lib/test/test_concurrent_futures.py +++ b/Lib/test/test_concurrent_futures.py @@ -18,6 +18,7 @@ import sys import threading import time import unittest +import warnings import weakref from pickle import PicklingError @@ -571,6 +572,24 @@ class ProcessPoolShutdownTest(ExecutorShutdownTest): 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, diff --git a/Lib/test/test_fcntl.py b/Lib/test/test_fcntl.py index fc8c393..113c780 100644 --- a/Lib/test/test_fcntl.py +++ b/Lib/test/test_fcntl.py @@ -1,11 +1,11 @@ """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 @@ -160,7 +160,8 @@ class TestFcntl(unittest.TestCase): 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) @@ -171,7 +172,8 @@ class TestFcntl(unittest.TestCase): 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) diff --git a/Lib/test/test_logging.py b/Lib/test/test_logging.py index 072056d..8a12d57 100644 --- a/Lib/test/test_logging.py +++ b/Lib/test/test_logging.py @@ -4759,8 +4759,9 @@ class LogRecordTest(BaseTest): # 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,) ) diff --git a/Lib/test/test_multiprocessing_defaults.py b/Lib/test/test_multiprocessing_defaults.py new file mode 100644 index 0000000..1da4c06 --- /dev/null +++ b/Lib/test/test_multiprocessing_defaults.py @@ -0,0 +1,82 @@ +"""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() diff --git a/Lib/test/test_pickle.py b/Lib/test/test_pickle.py index 44fdca7..80e7a4d 100644 --- a/Lib/test/test_pickle.py +++ b/Lib/test/test_pickle.py @@ -533,6 +533,8 @@ class CompatPickleTests(unittest.TestCase): 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)) diff --git a/Lib/test/test_re.py b/Lib/test/test_re.py index 11628a2..eacb1a7 100644 --- a/Lib/test/test_re.py +++ b/Lib/test/test_re.py @@ -2431,7 +2431,8 @@ class ReTests(unittest.TestCase): 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: diff --git a/Misc/NEWS.d/next/Library/2023-01-01-01-19-33.gh-issue-84559.zEjsEJ.rst b/Misc/NEWS.d/next/Library/2023-01-01-01-19-33.gh-issue-84559.zEjsEJ.rst new file mode 100644 index 0000000..3793e0f --- /dev/null +++ b/Misc/NEWS.d/next/Library/2023-01-01-01-19-33.gh-issue-84559.zEjsEJ.rst @@ -0,0 +1,11 @@ +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``. |