[Python-Dev] Py_CLEAR to avoid crashes
Neil Schemenauer
nas at arctrix.com
Mon Feb 18 22:52:14 CET 2008
On Mon, Feb 18, 2008 at 05:48:57PM +0100, Amaury Forgeot d'Arc wrote:
> For example, in exception.c, BaseException_init() starts with the instruction:
> Py_DECREF(self->args);
> this may call __del__ on self->args
Ah, I understand now. We are not talking about tp_dealloc methods
(the GC takes great pains to avoid this scenario). However, any
object that calls Py_DECREF outside of its tp_dealloc method must be
prepared for finalizers to access it in arbitrary ways.
That sucks. Most Py_DECREF calls are probably okay but it's going
to be hard to find the ones that are not. I can't think of anything
we can do to make this trap harder to fall into. Even using
Py_CLEAR as a blunt tool is not a total solution. You could still
end up with a null pointer dereference if the code is not written
carefully.
Neil
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