New submission from Kevin Shweh <kevin.sh...@gmail.com>:
This code in Thread._wait_for_tstate_lock:
try:
if lock.acquire(block, timeout):
lock.release()
self._stop()
except:
if lock.locked():
# bpo-45274: lock.acquire() acquired the lock, but the function
# was interrupted with an exception before reaching the
# lock.release(). It can happen if a signal handler raises an
# exception, like CTRL+C which raises KeyboardInterrupt.
lock.release()
self._stop()
raise
has a bug. The "if lock.locked()" check doesn't check whether this code managed
to acquire the lock. It checks if *anyone at all* is holding the lock. The lock
is almost always locked, so this code will perform a spurious call to
self._stop() if it gets interrupted while trying to acquire the lock.
Thread.join uses this method to wait for a thread to finish, so a thread will
spuriously be marked dead if you interrupt a join call with Ctrl-C while it's
trying to acquire the lock. Here's a reproducer:
import time
import threading
event = threading.Event()
def target():
event.wait()
print('thread done')
t = threading.Thread(target=target)
t.start()
print('joining now')
try:
t.join()
except KeyboardInterrupt:
pass
print(t.is_alive())
event.set()
Interrupt this code with Ctrl-C during the join(), and print(t.is_alive()) will
print False.
----------
components: Library (Lib)
messages: 413106
nosy: Kevin Shweh
priority: normal
severity: normal
status: open
title: Thread spuriously marked dead after interrupting a join call
type: behavior
versions: Python 3.10, Python 3.11, Python 3.9
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue46726>
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