python多線程實現異步

import time
from threading import Thread


def long_io(cb):
    def func(callback):
        print("開始耗時操作io")
        time.sleep(5)
        print("io耗時操作完成")
        res = "io res"
        callback(res)

    t1 = Thread(target=func, args=(cb,))
    t1.start()


def receive_msg(res):
    print("獲取結果回調結果")
    print("io 結果:", res)


def req_a():
    print("開始處理請求a---")
    long_io(receive_msg)
    print("離開請求a")


def req_b():
    print("開始處理請求B")
    time.sleep(2)
    print("處理完請求B")


def main():
    req_a()
    req_b()


if __name__ == '__main__':
    main()