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_at_fork() has a bug: it creates a _DummyThread instead of a _MainThread. Example:
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import os, _thread, threading, time
def fork_in_thread():
 pid = os.fork()
 if pid:
 # parent
 os._exit(0)
 # child process
 print(f"child process: {threading.current_thread()=}")
 print(f"child process: {threading._main_thread=}")
print(f"parent process: {threading.current_thread()=}")
print(f"parent process: {threading._main_thread=}")
_thread.start_new_thread(fork_in_thread, ())
# block the main thread: fork_in_thread() exit the process
time.sleep(60)
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Output:
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parent process: threading.current_thread()=<_MainThread(MainThread, started 139879200077632)>
parent process: threading._main_thread=<_MainThread(MainThread, started 139879200077632)>
child process: threading.current_thread()=<_DummyThread(Dummy-1, started daemon 139878980245248)>
child process: threading._main_thread=<_DummyThread(Dummy-1, started daemon 139878980245248)>
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My PR 19191 fix the issue:
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parent process: threading.current_thread()=<_MainThread(MainThread, started 140583665170240)>
parent process: threading._main_thread=<_MainThread(MainThread, started 140583665170240)>
child process: threading.current_thread()=<_MainThread(MainThread, started 140583445075712)>
child process: threading._main_thread=<_MainThread(MainThread, started 140583445075712)>
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