[Python-Dev] Better module shutdown procedure

Benjamin Peterson benjamin at python.org
Fri Oct 16 16:11:17 CEST 2009

2009/10/16 Amaury Forgeot d'Arc <amauryfa at gmail.com>:
> 2009/10/16 Neil Schemenauer <nas at arctrix.com>:
>> After some experimentation I realize this idea is not ready yet.
>> The main problem comes from references to Python objects that
>> modules keep but don't expose to the garbage collector. For example,
>> gcmodule.c has a static pointer "tmod" that is a reference to the
>> "time" module. This reference prevents the "time" module from being
>> freed during interpreter shutdown.
>> Ideally, I suppose modules should be treated like any other object
>> and have tp_traverse and tp_clear methods that deal with these sorts
>> of pointers. They would have to delegated to the instance since each
>> module would have its own implementation.
> Note since python 3.0 (and PEP 3121), the PyModuleDef structure has
> some members like m_traverse, m_clear and m_free for this very
> purpose.
> So far, nobody cared to implement these methods for any module. Maybe
> one should start at least for static PyObject* that contain references
> to modules.

I believe the implementation is buggy because modules (and their
states) can easily be finalized before the objects contained in them.
For example, when I tried to convert the _io module to use a state, it
resulted in segfaults when the dealloc methods of objects tried to use
objects in a state, which had already been deallocated.


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