After applying the PRs in issue34172, multiprocessing.Pool.imap hangs on MacOs and Linux. This is a simple reproducer:

import multiprocessing

def the_test():
    print("Begin")
    for x in multiprocessing.Pool().imap(int,
            ["4", "3"]):
        print(x)
    print("End")

the_test()

This happens because the IMapIterator does not maintain alive the multiprocessing.Pool object while it is still alive.