Re: Bug in threading.Thread.join() ?
Peter Hansen wrote: I'll take your last sentence as a form of blessing to go file a bug report... Filed as http://sourceforge.net/tracker/index.php?func=detail&aid=1171023&group_id=5470&atid=105470 I guess it makes more sense for any further discussion to go on there... (Coincidentally, another bug report was filed just a few days ago for a closely related item. As Tim mentioned, the wait() without a timeout can never be interrupted by Ctrl-C, and somebody else reported that as a bug (1167930) only about three days before I encountered this one.) -Peter -- http://mail.python.org/mailman/listinfo/python-list
Re: Bug in threading.Thread.join() ?
Tim Peters wrote: [Peter Hansen] If you hit Ctrl-C while the join's wait() is occurring, you'll raise a KeyboardInterrupt and bypass the release() call. Then you're doing something other than what you described. Here on WinXP SP2 w/ Python 2.4c2: [snip] 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. 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. Yes, definitely doing this with a timeout value on the join(). Changing your example to do that (join(5), say) pretty much demonstrates the trouble... in this case a traceback for KeyboardInterrupt is printed, but the program does not terminate because of the thread stuck at the __stop()'s __acquire(). I'll take your last sentence as a form of blessing to go file a bug report, unless you don't think that's a good idea. Thanks, Tim! -Peter -- http://mail.python.org/mailman/listinfo/python-list
Re: Bug in threading.Thread.join() ?
[Peter Hansen] > 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: ... time.sleep(1) ... >>> t =T() >>> t.start() >>> t.join() 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. -- http://mail.python.org/mailman/listinfo/python-list
Bug in threading.Thread.join() ?
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.) 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? I'll file a bug report shortly unless someone can point out the error in my reasoning or a reason why this must be the way it is. -Peter -- http://mail.python.org/mailman/listinfo/python-list