Feature or enhancement

The warnings implementation is split between Python (warnings.py) and C (_warnings.c). There are a few bits of code in the C module that are not thread-safe without the GIL:

The Py_SETREF calls are not thread-safe if concurrent writers try to overwrite the same field (e.g., st->once_registry). We can probably use critical sections to make it thread-safe.

get_once_registry:

get_default_action:

get_filter:

Some uses of borrowed references are likely not thread-safe

• _PyDict_GetItemWithError (replace with PyDict_GetItemRef?)

Linked PRs

• gh-116664: Ensure thread-safe dict access in _warnings #116768
• gh-116664: Make module state Py_SETREF's in _warnings thread-safe #116959
• gh-116664: Fix unused var warnings in _warnings.c in non-free-threaded builds #117373
• gh-116664: In _warnings.c, make filters_version access thread-safe #117374