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fix: Unregister semaphores from stdlib tracker immediately after creation #474

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fix: Unregister semaphores from stdlib tracker immediately after creation #474

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c144380
Fix semaphore leak warnings on Python 3.13+
m0nas Nov 22, 2025
93d882b
fix: Unregister semaphores from stdlib tracker immediately after crea…
m0nas Nov 22, 2025
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24 changes: 24 additions & 0 deletions loky/backend/synchronize.py
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,13 @@
from multiprocessing import process, util
from multiprocessing.context import assert_spawning

# Import Python's stdlib resource_tracker to unregister semaphores from it
# This prevents "leaked semaphore" warnings on Python 3.13+ when loky manages cleanup
try:
from multiprocessing import resource_tracker as stdlib_resource_tracker
except ImportError:
stdlib_resource_tracker = None

from . import resource_tracker

__all__ = [
Expand Down Expand Up @@ -72,6 +79,14 @@ def __init__(self, kind, value, maxvalue, name=None):
self._semlock = _SemLock(
kind, value, maxvalue, SemLock._make_name(), unlink_now
)
# FIX: Unregister from stdlib resource_tracker immediately after creation
# to prevent "leaked semaphore" warnings on Python 3.13+
if stdlib_resource_tracker is not None:
try:
stdlib_resource_tracker.unregister(self._semlock.name, "semlock")
except (KeyError, ValueError):
# Semaphore wasn't registered in stdlib tracker, that's fine
pass
except FileExistsError: # pragma: no cover
pass
else:
Expand All @@ -80,6 +95,14 @@ def __init__(self, kind, value, maxvalue, name=None):
raise FileExistsError("cannot find name for semaphore")
else:
self._semlock = _SemLock(kind, value, maxvalue, name, unlink_now)
# FIX: Unregister from stdlib resource_tracker immediately after creation
# to prevent "leaked semaphore" warnings on Python 3.13+
if stdlib_resource_tracker is not None:
try:
stdlib_resource_tracker.unregister(self._semlock.name, "semlock")
except (KeyError, ValueError):
# Semaphore wasn't registered in stdlib tracker, that's fine
pass
self.name = name
util.debug(
f"created semlock with handle {self._semlock.handle} and name "
Expand All @@ -96,6 +119,7 @@ def _after_fork(obj):
# When the object is garbage collected or the
# process shuts down we unlink the semaphore name
resource_tracker.register(self._semlock.name, "semlock")

util.Finalize(
self, SemLock._cleanup, (self._semlock.name,), exitpriority=0
)
Expand Down