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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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19
Lib/test/test_concurrent_futures.py
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@ -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,