Ok, so two test cases 1) from multiprocessing.pool import ThreadPool class A(object): def __init__(self): self.pool = ThreadPool() def __del__(self): self.pool.close() self.pool.join() a = A() print(a) 2) from multiprocessing import Pool class A: def __init__(self): self.pool = Pool(processes=1) def test(): problem = A() problem.pool.map(float, tuple(range(10))) if __name__ == "__main__": test() On two my test environments with Linux, 5.5.2 and 4.9.208 kernel, glibc 2.31 (userspace is mostly the same on both) test 1) hangs, 2) doesn't hang. Testing done on 3.8 branch + https://patch-diff.githubusercontent.com/raw/python/cpython/pull/19023.patch For test 1) no traceback on ctrl+c and also no trace logged with faulthandler installed, so no idea where it hangt. strace shows [...] [pid 232031] munmap(0x7f1baaffe000, 8392704 <unfinished ...> [pid 232017] write(5, "\0\0\0\4\200\4N.", 8 <unfinished ...> [pid 232031] <... munmap resumed>) = 0 [pid 232017] <... write resumed>) = 8 [pid 232031] exit(0) = ? [pid 232017] futex(0x7f1b94000b60, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL, FUTEX_BITSET_MATCH_ANY <unfinished ...> [pid 232031] +++ exited with 0 +++ ^C ************************* ctrl + c pressed [pid 232017] <... futex resumed>) = ? ERESTARTSYS (To be restarted if SA_RESTART is set) strace: Process 232017 detached strace: Process 232032 detached strace: Process 232033 detached strace: Process 232034 detached strace: Process 232035 detached