multiprocessing async .get() hangs if the pool is terminated

Bug report

Bug description:

MWE

Steps to reproduce:

import multiprocessing
from time import sleep

with multiprocessing.Pool() as p:
    result = p.apply_async(sleep, (1,))
result.get()

Expected behavior:

Either:

• result is returned. (Pool().__exit__ waits for every async task to finish); or
• some kind of exception is raised when .get() is called outside with Pool()

Comments

This is the same as #79659. That was marked as completed in 2021. However it seems the issue is still present.

CPython versions tested on:

3.12, 3.13, 3.14

Operating systems tested on:

Linux

Comienza ejecutando el MWE proporcionado y siguiendo la interacción entre Pool.exit y la llamada .get() del resultado asíncrono después de que el pool haya terminado. Compara el comportamiento con el issue #79659 y añade cobertura para el resultado esperado documentado: finalización o una excepción en lugar de un bloqueo.