Crash when inspecting frame of other thread in free-threaded build about cpython

[colesbury]

Yeah, this function is not thread-safe. We need to figure out what to do about it.

More precisely, the call sys._current_frames() is okay, but accessing other thread's frames while they are running is not thread-safe without the GIL.

[savannahostrowski]

I can't reproduce the crash on a Mac (M3 Pro), in case that's helpful!

[erlend-aasland]

I can repro on a MacBook Pro (M1), using ./configure --disable-gil --with-pydebug && make:

$ ./python.exe ./crash.py
Assertion failed: (frame->frame_obj == NULL), function _PyFrame_MakeAndSetFrameObject, file frame.c, line 48.
[1]    27564 abort      ./python.exe ./crash.py
$ ./python.exe -VV
Python 3.13.0a6+ (heads/main-dirty:d3c7821335, May  7 2024, 09:27:50) [Clang 15.0.0 (clang-1500.3.9.4)]
$ ./python.exe -c "import sys; print(sys._is_gil_enabled())"
False