Crash when modifying DLL function pointers conconcurrently

[ZeroIntensity]

It seems that ctypes doesn't like having function pointers on a CDLL modified concurrently. Here's a reproducer (for Linux):

import ctypes
from threading import Thread

dll = ctypes.CDLL("libc.so.6")

def main():
    for _ in range(100):
        dll.puts.argtypes = ctypes.c_char_p,
        dll.puts.restype = ctypes.c_int

threads = [Thread(target=main) for _ in range(100)]
for thread in threads:
    thread.start()

Linked PRs

• gh-127946: Use a critical section for CFuncPtr attributes #128109

[ZeroIntensity]

PR ready, but waiting on #127950.