gh-120321: Make gi_frame_state transitions atomic in FT build by colesbury · Pull Request #142599 · python/cpython

Co-authored-by: Kumar Aditya <kumaraditya@python.org>

Also use it in both the default and FT builds.

Generator calls may be nested so it's not sufficient to set the field
before the call to PyEval_Frame.

Co-authored-by: Kumar Aditya <kumaraditya@python.org>

…ythongh-142599)

This makes generator frame state transitions atomic in the free
threading build, which avoids segfaults when trying to execute
a generator from multiple threads concurrently.

There are still a few operations that aren't thread-safe and may crash
if performed concurrently on the same generator/coroutine:

 * Accessing gi_yieldfrom/cr_await/ag_await
 * Accessing gi_frame/cr_frame/ag_frame
 * Async generator operations