[Taking this to email. Carrying out discussions via the SF bug tracker sucks.] Comment By: Tim Peters (tim_one)
[Neil]
I had to change _PyWeakref_ClearRef() since it was also clearing the weakref list of the trash object.
That was really its *purpose*. If a trash weakref with a callback isn't removed from the referent's list of weakrefs, then the callback will trigger when PyObject_ClearWeakRefs() is invoked on the referent. The purpose of _PyWeakref_ClearRef() was to ensure that the callback never triggers.
But it's okay of the callback triggers, as long as the callback doesn't reference trash.
Now it just sets wr_object to Py_None.
That won't stop the callback from triggering. It also means (see earlier comment) that PyObject_ClearWeakRefs() will never removed the weakref from the list either, although I'm not sure that does real harm.
I'm trying to figure out PyObject_ClearWeakRefs() right now.
I also made some serious simplifications to gcmodule by just treating trash weakref objects with callbacks the same as objects with __del__ methods (i.e. move them to the finalizers list and then do the transitive closure of that set).
Does that mean they can end up in gc.garbage too? If so, I don't think that's sellable.
I think so. That can be easily changed though. What we can't do is invoke those callbacks. Neil