[Python-Dev] second opinion for proposed fix for bug #754449

[Guido van Rossum]

> So http://python.org/sf/754449 is a bug report about threading and an 
> exception being raised when the interpreter is being shut down, setting 
> a function in threading to None because of teardown, and then trying to 
> execute that now killed function in the shutdown code for 
> threading.Thread (what a mouthful).

Ouch.

> Basically the exception stems from a call to threading.currentThread in 
> the _Condition class (which is just Condition) which, according to the 
> comment along with the call, is just for its side-effect.  Well, I 
> looked and I can't find the need for the side-effect.  I took out the 
> code and ran the regression tests and nothing failed because of it.
> 
> Since the code says the call is for the explicit side-effect I just 
> wanted another pair of eyes to quickly scan the code in threading.py and 
> either agree with me or tell me I am blind and point out where the 
> side-effect is needed for Condition instances.  The offending 
> currentThread calls can be found on lines 196 and 238 (can also just 
> search for "side-effect" to find them).

This is my code.  It was long ago.  I think the intended side effect
is creating a dummy thread *IF* the calling thread was not created by
the threading module but by thread.start_new_thread().  The current
thread in turn is only relevant when the Condition's lock is an RLock.
But the only thing that is ever done with that is comparing it with
the outcome of another call to currentThread().  So I *THINK* that the
side effect isn't particularly needed.

(But the threading module references other globals, so I'm not sure
that ripping out the currentThread() calls is really enough, except in
this particular app's case.)

--Guido van Rossum (home page: http://www.python.org/~guido/)