> is there a bulletproof way to guarantee that `self._stop()` gets 
> called if the acquire_and_release() succeeds? 

I don't think it's critical. But we still should deal with the common case in Windows in which a KeyboardInterrupt is raised immediately after the method returns. For example:

        try:
            if lock.acquire_and_release(block, timeout):
                self._stop
        except:
            if not lock.locked():
                self._stop()

The proposed acquire_and_release() method can also be used in threading._shutdown(), when it iterates _shutdown_locks to join non-daemon threads.