bpo-40091: Fix a hang at fork in the logging module (GH-19416)
Fix a hang at fork in the logging module: the new private _at_fork_reinit() method is now used to reinitialize locks at fork in the child process. The createLock() method is no longer used at fork.
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@ -234,11 +234,9 @@ if not hasattr(os, 'register_at_fork'): # Windows and friends.
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def _register_at_fork_reinit_lock(instance):
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pass # no-op when os.register_at_fork does not exist.
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else:
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# A collection of instances with a createLock method (logging.Handler)
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# A collection of instances with a _at_fork_reinit method (logging.Handler)
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# to be called in the child after forking. The weakref avoids us keeping
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# discarded Handler instances alive. A set is used to avoid accumulating
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# duplicate registrations as createLock() is responsible for registering
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# a new Handler instance with this set in the first place.
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# discarded Handler instances alive.
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_at_fork_reinit_lock_weakset = weakref.WeakSet()
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def _register_at_fork_reinit_lock(instance):
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@ -249,16 +247,12 @@ else:
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_releaseLock()
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def _after_at_fork_child_reinit_locks():
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# _acquireLock() was called in the parent before forking.
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for handler in _at_fork_reinit_lock_weakset:
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try:
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handler.createLock()
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except Exception as err:
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# Similar to what PyErr_WriteUnraisable does.
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print("Ignoring exception from logging atfork", instance,
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"._reinit_lock() method:", err, file=sys.stderr)
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_releaseLock() # Acquired by os.register_at_fork(before=.
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handler._at_fork_reinit()
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# _acquireLock() was called in the parent before forking.
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# The lock is reinitialized to unlocked state.
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_lock._at_fork_reinit()
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os.register_at_fork(before=_acquireLock,
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after_in_child=_after_at_fork_child_reinit_locks,
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@ -891,6 +885,9 @@ class Handler(Filterer):
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self.lock = threading.RLock()
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_register_at_fork_reinit_lock(self)
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def _at_fork_reinit(self):
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self.lock._at_fork_reinit()
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def acquire(self):
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"""
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Acquire the I/O thread lock.
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@ -2168,6 +2165,9 @@ class NullHandler(Handler):
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def createLock(self):
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self.lock = None
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def _at_fork_reinit(self):
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pass
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# Warnings integration
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_warnings_showwarning = None
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@ -0,0 +1,2 @@
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Fix a hang at fork in the logging module: the new private _at_fork_reinit()
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method is now used to reinitialize locks at fork in the child process.
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