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gh-108520: Fix bad fork detection in nested multiprocessing use case (#108568)

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gh-107275 introduced a regression where a SemLock would fail being passed along nested child processes, as the `is_fork_ctx` attribute would be left missing after the first deserialization.

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Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>
Co-authored-by: Antoine Pitrou <pitrou@free.fr>
This commit is contained in:
albanD 2023-08-30 13:07:41 -04:00 • committed by GitHub
parent 2a3926fa51
commit add8d45cbe
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3 changed files with 34 additions and 3 deletions
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8
Lib/multiprocessing/synchronize.py
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@ -50,8 +50,8 @@ class SemLock(object):
def __init__(self, kind, value, maxvalue, *, ctx):
if ctx is None:
ctx = context._default_context.get_context()
self.is_fork_ctx = ctx.get_start_method() == 'fork'
unlink_now = sys.platform == 'win32' or self.is_fork_ctx
self._is_fork_ctx = ctx.get_start_method() == 'fork'
unlink_now = sys.platform == 'win32' or self._is_fork_ctx
for i in range(100):
try:
sl = self._semlock = _multiprocessing.SemLock(
@ -103,7 +103,7 @@ class SemLock(object):
if sys.platform == 'win32':
h = context.get_spawning_popen().duplicate_for_child(sl.handle)
else:
if self.is_fork_ctx:
if self._is_fork_ctx:
raise RuntimeError('A SemLock created in a fork context is being '
'shared with a process in a spawn context. This is '
'not supported. Please use the same context to create '
@ -115,6 +115,8 @@ class SemLock(object):
self._semlock = _multiprocessing.SemLock._rebuild(*state)
util.debug('recreated blocker with handle %r' % state[0])
self._make_methods()
# Ensure that deserialized SemLock can be serialized again (gh-108520).
self._is_fork_ctx = False
@staticmethod
def _make_name():