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[Python-Dev] Py_CLEAR to avoid crashes

"Martin v. Löwis" martin at v.loewis.de
Sun Feb 17 21:29:24 CET 2008 
Jeffrey Yasskin wrote:
> On Feb 16, 2008 3:12 PM, Amaury Forgeot d'Arc <amauryfa at gmail.com> wrote:
>> Should we however intensively search and correct all of them?
>> Is there a clever way to prevent these problems globally, for example
>> by delaying finalizers "just a little"?
> 
> A simple way to do this would be to push objects whose refcounts had
> reached 0 onto a list instead of finalizing them immediately, and have
> PyEval_EvalFrameEx periodically swap in a new to-delete list and
> delete the objects on the old one.

-1. This would only soften the problem in a shallow way. It should still
be possible to create cases where the final cleanup of the object comes
"too early", e.g. when some caller of PyEval_EvalFrameEx still carries
a pointer to some object that got deleted, and then still some code can
get hold of the then-deleted object. It will just be more difficult to
trigger such crashes, depending on the period in which objects are
cleaned.

The only sane way to never touch deleted objects is to have no 
references to them on heap anymore, and to not touch stack references
after the DECREF.

Regards,
Martin
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