Describe the bug

When using multiprocessing Pool, the application hangs on get()
It will hang on close() also.

Code to reproduce the behaviour:

# example code
import multiprocessing as mp


def do_print(value):
    print(value)
    return f'Done {value}'


def main():
    pool = mp.Pool(mp.cpu_count())

    results = []

    results.append(pool.apply_async(do_print, ['uno']))

    for r in results:
        print(r.get())


if __name__ == '__main__':
    main()

Expected behaviour

Output:

uno
Done uno

OS

Linux Ubuntu 24.0.4 6.8.0-79-generic 79-Ubuntu SMP PREEMPT_DYNAMIC Tue Aug 12 14:42:46 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux

Python version

3.12.3

Cython version

3.1.3, 3.0.8

Additional context

compilation:

  cython -3 --embed test.pyx
  gcc -o test test.c -I /usr/include/python3.12 -Wl,-rpath,/usr/lib/x86_64-linux-gnu/libpython3.12.so /usr/lib/x86_64-linux-gnu/libpython3.12.so