Bug in threading.Thread.join() ?
tim.peters at gmail.com
Sat Mar 26 06:33:05 CET 2005
> I'm still trying to understand the behaviour that I'm
> seeing but I'm already pretty sure that it's either
> a bug, or something that would be considered a bug if
> it didn't perhaps avoid even worse behaviour.
> Inside the join() method of threading.Thread objects,
> a Condition named self.__block is acquired, and then
> the wait logic is executed. After the wait() finishes,
> self.__block is released and the method returns.
> If you hit Ctrl-C while the join's wait() is occurring,
> you'll raise a KeyboardInterrupt and bypass the
> release() call.
> (I'm observing this on Win XP with
> Python 2.4 but have no reason to think it wouldn't
> work the same on other platforms, given the docs
> on signals and such.)
Then you're doing something other than what you described. Here on
WinXP SP2 w/ Python 2.4c2:
>>> import threading
>>> class T(threading.Thread):
... def run(self):
... import time
... while True:
>>> t =T()
I can hit Ctrl+C all day at this point, and nothing (visible) happens.
That's because it's sitting in self.__block.wait(), which is in turn
sitting in waiter.acquire(), and it's simply not possible for Ctrl+C
to interrupt a mutex acquire.
> If you do this, the thread you were waiting for will never be able
> to complete its cleanup because __bootstrap() calls __stop()
> and that tries to acquire the same Condition object,
> which has never been released. (I suspect this will
> happen only if its the MainThread that is doing
> the join() call since KeyboardInterrupts only occur
> in the main thread.)
> A simple try/finally in join() appears to solve the
> problem, but I'm unsure that this is a good idea,
> partly because I'm a little surprised nobody else has
> found this problem before and I lack confidence that
> I've really found a bug.
> Anyone have thoughts on this?
As above, I don't know what you're doing. Maybe you're doing a join()
with a timeout too? In that case, I doubt anyone gave any thought to
what happens if you muck with KeyboardInterrupt too.
More information about the Python-list