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Fri Oct 29 22:22:11 CEST 2004 · https://mail.python.org/pipermail/python-dev/2004-October/049709.html

On Fri, Oct 29, 2004 at 03:59:37PM -0400, Tim Peters wrote:
> if clear_weakref doesn't know what the referent is, it can't find
> the pointer to the head of the referent's weakref list, so it
> can't unlink W from the list correctly (unlike gc's doubly-linked
> lists, weakref lists aren't circular, and don't have list heads)
> This leaves free'd memory *in* the referent's weakref list.  So if
> the referent's refcount falls to 0 after that, then
> PyObject_ClearWeakRefs() goes nuts trying to crawl over the freed
> memory.

Crap.  That's got to be the problem that I've been bashing my head
against for the past few hours.  Okay, how about we first clearly
specify what needs to happen.  Afterwards we can figure how to
do it while retaining binary compatibility. :-(

Non-trash weakrefs to trash objects MUST have their callbacks
invoked.  Trash weakrefs MUST NOT have their callbacks invoked.  Any
weakref to a trash object MUST NOT reveal the trash (i.e. via the
wr_object pointer).

Does that sound correct?

  Neil

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[Python-Dev] Re: weakref callback vs gc vs threads