gh-126366: Make native generators thread safe

[ZeroIntensity]

Co-authored-by: Ken Jin [email protected]

• Issue: Abort in free-threaded build due to mutation of ChainMap of a Counter in threads #126366

[corona10]

cc @colesbury

[corona10]

I will try to take a look at today :)

[ZeroIntensity]

Closing in favor of #120327

[Fidget-Spinner]

Wait I closed my PR in favour of yours... 😆 @ZeroIntensity

[ZeroIntensity]

Ah! I'll reopen this and list you as a co-author if yours has merge conflicts.

[vstinner]

There is a warning:

Check warning on line 129 in Python/ceval_macros.h
‘gen_frame’ may be used uninitialized in this function [-Wmaybe-uninitialized]

[vstinner]

The overall approach LGTM. I'm feeling more confortable with more critical sections :-)

[colesbury]

• Let's avoid critical sections in bytecodes.c. It's too easy to make these kinds of mistakes where you exit out of a critical section without ending it.
• I don't think the generator running thread safety should use critical sections. We should use something like an atomic-compare-exchange to mark it as running