import multiprocessing as mp import time def foo_pool(x): time.sleep(2) return x*x result_list = [] def log_result(result): # This is called whenever foo_pool(i) returns a result. # result_list is modified only by the main process, not the pool workers. result_list.append(result) def apply_async_with_callback(): pool = mp.Pool() for i in range(10): pool.apply_async(foo_pool, args = (i, ), callback = log_result) pool.close() pool.join() print(result_list) if __name__ == '__main__': apply_async_with_callback()