[Python-Dev] Re: [PythonLabs] Re: [Python-checkins]python/dist/src/Modules gcmodule.c,126.96.36.199,188.8.131.52
Sat, 5 Apr 2003 03:15:40 -0500
> We've got the first version of boom nailed, but we've got the same
> problem in handle_finalizers(). The version of boom below doesn't blow
> up until the second time the has_finalizer() is called.
> I don't understand the logic in handle_finalizers(), though. If the
> objects are all in the finalizers list, why do we call has_finalizer() a
> second time? Shouldn't everything has a finalizer at that point?
Nope -- the parenthetical
/* Handle uncollectable garbage (cycles with finalizers). */
comment is incomplete. The earlier call to move_finalizer_reachable() also
put everything reachable only *from* trash cycles with finalizers into the
list. So, e.g., if the trash graph is like
and A has a finalizer but B and C don't, they're all in the finalizers list
(at this point) regardless. But B and C aren't stopping the blob from
getting collected, and we're trying to do the user a favor by putting only A
(the troublemaker) into gc.garbage. It's an approximation, though. For
example, if A and C both had finalizers, A and C would both be put into
gc.garbage, despite that C's finalizer isn't stopping anything from getting
The comments are apparently a bit out of synch with the code, because 17
months ago all instance objects in the finalizers list were put into
gc.garbage (regardless of whether they had __del__). The checkin comment
for rev 2.28 sez the __del__ change was needed to fix a bug; but I'm too
groggy to dig more now.