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gh-135726: multiprocessing.freeze_support no longer sets the start method globally. #135810

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gh-135726: multiprocessing.freeze_support no longer sets the start method globally. #135810

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3d383d7
multiprocessing.freeze_support no longer sets the start method globally.
aisk Jun 22, 2025
d566cf6
Update BaseContext.freeze_support instead of override it
aisk Jun 26, 2025
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15 changes: 12 additions & 3 deletions Lib/multiprocessing/context.py
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Original file line number Diff line number Diff line change
Expand Up @@ -145,9 +145,18 @@ def freeze_support(self):
'''Check whether this is a fake forked process in a frozen executable.
If so then run code specified by commandline and exit.
'''
if self.get_start_method() == 'spawn' and getattr(sys, 'frozen', False):
from .spawn import freeze_support
freeze_support()
if not getattr(sys, 'frozen', False):
return

# GH-135726: allow_none=True prevents this "get" call from setting the
# default context as the selected one as a side-effect.
method = self.get_start_method(allow_none=True) \
or _default_context.get_start_method(allow_none=True)
if method != "spawn":
return

from .spawn import freeze_support
freeze_support()

def get_logger(self):
'''Return package logger -- if it does not already exist then
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7 changes: 7 additions & 0 deletions Lib/test/_test_multiprocessing.py
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Expand Up @@ -5823,6 +5823,13 @@ def test_context(self):
self.assertRaises(ValueError, ctx.set_start_method, None)
self.check_context(ctx)

def test_freeze_support_side_effect(self):
# GH-135726: freeze_support() should not set the start method
# as a side-feect,
multiprocessing.set_start_method(None, force=True)
multiprocessing.freeze_support()
self.assertIsNone(multiprocessing.get_start_method(allow_none=True))

def test_context_check_module_types(self):
try:
ctx = multiprocessing.get_context('forkserver')
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2025-06-22-15-42-10.gh-issue-135726._oO5IN.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
:func:`multiprocessing.freeze_support` no longer sets the start method
globally.
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