bpo-40077: Convert _abc module to use PyType_FromSpec()

[corona10]

Replace statically allocated types with heap allocated types:
use PyType_FromSpec().

Add a module state to store the _abc_data_type..
Add traverse, clear and free functions to the module.

https://bugs.python.org/issue40077

[corona10]

I am not sure that the abc_invalidation_counter is okay to be shared as static from interpreter Isolation point of view.

[corona10]

Should we move this into PyInterpreterState?

[vstinner]

It seems like it would be safe to put it in the module state. The purpose of the counter is to invalidate the module cache. Registering a class in module instance 1 should not invalidate module instance 2. What do you think?

[corona10]

I agree, I 've updated the PR.

[corona10]

This test might be what we wanted exactly.
I just updated the test for more validation.

[vstinner]

It seems like you cannot access to the module state in abc_data_new() which prevents you to move abc_invalidation_counter into the module state :-(

I suggest to leave abc_invalidation_counter as a "static" variable, but please add a FIXME like:

/* FIXME: PEP 573: Move abc_invalidation_counter into _abcmodule_state */

It's safe to keep it as a static variable until each interpreter gets its own GIL.

Until it happens, the change should move the module closer to the goal of isolated interpreters.

[corona10]

@vstinner
Thanks for the review.

PEP 573: Move abc_invalidation_counter into _abcmodule_state.

I agree, PEP 573 will solve this issue.
I 've updated the PR. Please take a look.

[corona10]

@vstinner Updated! Please take a look

[vstinner]

LGTM. Sorry, just one last change request, I promise ;-)

[vstinner]

Thanks, I merged your PR.