[Python-Dev] threading bug? (original) (raw)

Thomas Heller thomas.heller@ion-tof.com
Fri, 5 Oct 2001 21:04:00 +0200

From: "Guido van Rossum" <guido@python.org>

> [Apologies, I also asked this on c.l.p, but got no > answer so far. I have not too much time left before > I will be away for nearly 2 weeks] > > I wonder if this is a bug. I'm running a deamon thread doing > some work in the background, and sometimes when Python exits > I get tracebacks like this: > > Unhandled exception in thread: > Traceback (most recent call last): _> File "c:\python21\lib\threading.py", line 393, in bootstrap _> self.stop() _> File "c:\python21\lib\threading.py", line 399, in stop _> self.block.notifyAll() > File "c:\python21\lib\threading.py", line 235, in notifyAll _> self.notify(len(self.waiters)) > File "c:\python21\lib\threading.py", line 217, in notify > me = currentThread() > TypeError: object of type 'None' is not callable > > This traceback does not appear when I register an atexit > function to stop the thread. > > Is this a bug? Aren't daemon threads supposed to clean up > themselves?

This is probably a result of the destructive module finalization. When PyFinalize() is called, threads that are still running are not killed. But PyFinalize() replaces the values of all globals in modules with None (it could just clear the module's dictionary but there was some reason for doing it this way) and that is what you are probably seeing. If there was a primitive to kill a thread, we might use it in PyFinalize() -- but there isn't (it's been requested but it's hard to see how to do it safely).

But it seems the system is trying to stop the thread(s), maybe too late. In my case, atexit.register(self.stop) makes a clean shutdown. My point is: should the threading module do this? I can easily live with doing it myself - I just don't know if this is intended or required.

Thomas