[issue38006] Crash in remove() weak reference callback of weakref.WeakValueDictionary at Python exit
Tim Peters
report at bugs.python.org
Tue Oct 1 14:29:30 EDT 2019
Tim Peters <tim at python.org> added the comment:
Neil, about this comment:
# - ct is not yet trash (it actually is but the GC doesn't know because of
# the missing tp_traverse method).
I believe gc should know ct is trash. ct is in the cf list, and the latter does have tp_traverse.
What gc won't know is that `a` is trash, because `a` is attached to ct, and ct doesn't have tp_traverse.
It should blow up anyway :-)
Maybe with a simpler structure it would be easier to rearrange code to nudge the callback into getting cleared before use?
Z <- Y <- A <-> B -> WZ -> C
where WZ is a weakref to Z with callback C, and Y doesn't implement tp_traverse. The only cycle is between A and B, which could just as well be the same object. All the other stuff hangs off that cycle.
It's all trash, but we won't know in advance that Z is part of it.
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