gh-91632: Fix generic_alias_iterator to be finalized at exit.

[corona10]

AS-IS

➜  cpython git:(main) ✗ cat gh-91632.py
a = type(iter(tuple[int]))
print(a.mro())
➜  cpython git:(main) ✗ ./python.exe -X showrefcount gh-91632.py
[<class 'generic_alias_iterator'>, <class 'object'>]
[119 refs, 46 blocks]

TO-BE

➜  cpython git:(gh-91632) ✗ cat gh-91632.py
a = type(iter(tuple[int]))
print(a.mro())
➜  cpython git:(gh-91632) ✗ ./python.exe -X showrefcount gh-91632.py
[<class 'generic_alias_iterator'>, <class 'object'>]
[0 refs, 0 blocks]

Follow Victor's suggestion :)

closes: #91632

[Fidget-Spinner]

I can't review this since I have no clue on the process of freeing memory on exit. But when do we add a type to static_types? Is it always?

[vstinner]

I can't review this since I have no clue on the process of freeing memory on exit. But when do we add a type to static_types? Is it always?

I propose two approaches:

• Convert static types to heap types to free memory at exit: it's a hard work, and currently hold by the SC. You need to wait until https://peps.python.org/pep-0687/ is approved for that.

• Clear static types at Python exit (usually in Py_Finalize()):

  • Add the type to the static_types list in object.c (I tried to add all types there),
  • or: add a "Fini" function called by finalize_interp_types() (be careful of sub-interpreters: see _Py_IsMainInterpreter() function).

[vstinner]

LGTM.

[JelleZijlstra]

Should this be backported?

[Fidget-Spinner]

@JelleZijlstra No. Generic alias iterator is part of the variadic generics PEP which is 3.11 only iirc.

[vstinner]

Should this be backported?

The work to clear static types at exit is new in Python 3.11 (especially the _PyTypes_FiniTypes() function).