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

Inizia eseguendo l'MWE fornito e tracciando l'interazione tra Pool.exit e la chiamata .get() del risultato asincrono dopo la terminazione del pool. Confronta il comportamento con l'issue #79659 e aggiungi una copertura per l'esito atteso documentato: completamento o un'eccezione invece di un blocco.