gh-152666: Avoid reference counting of code objects

[brijkapadia]

Functions keep a list of past code objects so that a frame only needs borrowed references to them.

• Issue: Avoid refcounting on code objects during frame creation/destruction #152666

[markshannon]

The implementation of the old codes list looks good.
I'm wondering if the behavior, not the implementation, could be tested (or is it already?)

Also, can you make f_executable a PyObject * and always borrow it, to minimize overhead?

[bedevere-app]

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[brijkapadia]

I have made the requested changes; please review again

Unless I'm missing something (which is possible!) I do not think there is a way for generators to hold borrowed references without changing behavior.

[bedevere-app]

Thanks for making the requested changes!

@markshannon: please review the changes made to this pull request.

[markshannon]

Unless I'm missing something (which is possible!) I do not think there is a way for generators to hold borrowed references without changing behavior.

The generator is no different to the frame: it can borrow the reference to the code object, as long as it has a strong reference to the function. As the generator needs to keep a reference to the code object when cleared, it must also keep a reference to the function.

[brijkapadia]

@markshannon I've tried to implement borrowed references for generators but I've kept running into garbage collection issues with async generators in asyncio (even before this prior commit). There might be an easier solution that I'm missing but I'm not exactly sure how to resolve these issues cleanly.