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Add _at_fork_reinit() method to locks #84270
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Using a lock after fork() is unsafe and can crash. Example of a crash in logging after a fork on AIX: This problem is explained in length in bpo-6721: "Locks in the standard library should be sanitized on fork". The threading module registers an "at fork" callback: Thread._reset_internal_locks() is called to reset self._started (threading.Event) and self._tstate_lock. The current implementation creates new Python lock objects and forgets about the old ones. I propose to add a new _at_fork_reinit() method to Python lock objects which reinitializes the native lock internally without having to create a new Python object. Currently, my implementation basically creates a new native lock object and forgets about the old new (don't call PyThread_free_lock()). Tomorrow, we can imagine a more efficient impementation using platform specific function to handle this case without having to forget about the old lock. |
_at_fork() has a bug: it creates a _DummyThread instead of a _MainThread. Example: import os, _thread, threading, time
def fork_in_thread():
pid = os.fork()
if pid:
# parent
os._exit(0)
print(f"parent process: {threading.current_thread()=}") _thread.start_new_thread(fork_in_thread, ())
# block the main thread: fork_in_thread() exit the process
time.sleep(60) Output: My PR 19191 fix the issue: |
See also bpo-40091 "Crash in logging._after_at_fork_child_reinit_locks()" that I just created. |
See also bpo-40092: "Crash in _PyThreadState_DeleteExcept() at fork in the process child". |
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