gh-159041: Fix asyncio task tracking during thread state clear

[mikegit123git]

Fixes #159041

Summary

PyThreadState_Clear() currently merges the thread state's asyncio task
list before the Py_CLEAR() calls run finalizers. A finalizer can create
an asyncio Task after the merge, leaving the Task linked to a thread state
that is subsequently freed.

Move the task-list merge after all finalizer-capable cleanup operations and
add a regression test for a Task created by a thread-state finalizer.

Tests

• ./python -m test test_asyncio.test_free_threading -j0 (GIL build)
• ./python -m test test_asyncio.test_free_threading -j0 (free-threaded build)
• make patchcheck

• Issue: asyncio Task created from a finalizer during PyThreadState_Clear() registers into memory that is about to be freed (3.14 regression) #159041

[python-cla-bot]

All commit authors signed the Contributor License Agreement.

[BHUVANSH855]

Kindly sign CLA, so that maintainers can begin with review process.

[BHUVANSH855]

from the overview of changes, i just want to ask isn't this duplicate or overlaps with #159073

[mikegit123git]

Thanks for pointing this out!

I took a closer look at #159073, and you're right that both PRs address the same underlying issue.

There are some differences in the implementation and regression tests. This PR focuses on thread-state cleanup and tests task tracking with an event loop running in another thread, while #159073 also handles interpreter shutdown and moves the task-list merge further toward the end of PyThreadState_Clear().

I'm happy to defer to the maintainers on whether to consolidate the changes. Thanks again!