[WIP] gh-133931: Introduce _PyObject_XSetRefDelayed to replace Py_XSETREF

[corona10]

• Issue: Make generator methods gen_set_name and gen_set_qualname thread-safe in free-threaded builds #133931

[colesbury]

The default build implementation in pycore_pymem.h doesn't include the Py_NewRef().

My preference is to keep the Py_NewRef(value) in the callers, i.e.:

_PyObject_XSetRefDelayed(dictptr, Py_NewRef(value));

to match the semantics of Py_XSETREF.

[corona10]

Interesting... CI passed in my local but not in the CI.. :(

[corona10]

Ah okay..

test_aclose (test.test_asyncgen.TestUnawaitedWarnings.test_aclose) ... Assertion failed: (!_Py_IsImmortal(op)), function _Py_ExplicitMergeRefcount, file object.c, line 467.

[markshannon]

Why do we need _PyObject_XSetRefDelayed? It looks like all uses of it are wrapped in critical sections where the old Py_XSETREF would work.

Also, what is "delayed"? Either choose a clearer name, or add an explanatory comment in the header file.