Crash Due to Exception in threading._shutdown()#113148
Description
One of the first thing that happens during interpreter finalization is waiting for all non-daemon threads to finish. This is implemented by calling threading._shutdown(). If an exception is raised there (e.g. in a threading "atexit" function), it gets ignored and we end up with non-daemon threads still running. In subinterpreters that results in a fatal error almost immediately after, since we make sure there's only one thread state left at that point.
Reproducer:
$ cat > /tmp/crash-interp-lingering-thread.py << EOF import threading from test.support import interpreters interp = interpreters.create() interp.exec_sync(f"""if True: import threading import time done = False def notify_fini(): global done done = True raise Exception # <------- t.join() threading._register_atexit(notify_fini) def task(): while not done: time.sleep(0.1) t = threading.Thread(target=task) t.start() """) interp.close() EOF $ ./python /tmp/crash-interp-lingering-thread.py Exception ignored on threading shutdown: Traceback (most recent call last): File "./cpython/Lib/threading.py", line 1623, in _shutdown atexit_call() File "<string>", line 10, in notify_fini Exception: Fatal Python error: Py_EndInterpreter: not the last thread Python runtime state: initialized Current thread 0x00007fc8bf76a100 (most recent call first): <no Python frame> Thread 0x00007fc8bd3d5700 (most recent call first): File "<string>", line 16 in task File "./cpython/Lib/threading.py", line 1020 in run File "./cpython/Lib/threading.py", line 1083 in _bootstrap_inner File "./cpython/Lib/threading.py", line 1040 in _bootstrap Aborted (core dumped) The solution? Make sure threading._shutdown() finishes its fundamental job: stop all non-daemon threads and wait for them to finish. At the very least, this means ignoring exceptions from functions registered with threading._register_atexit().