python多线程实现异步

import time
from threading import Thread


def long_io(cb):
    def func(callback):
        print("开始耗时操作io")
        time.sleep(5)
        print("io耗时操作完成")
        res = "io res"
        callback(res)

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


def receive_msg(res):
    print("获取结果回调结果")
    print("io 结果:", res)


def req_a():
    print("开始处理请求a---")
    long_io(receive_msg)
    print("离开请求a")


def req_b():
    print("开始处理请求B")
    time.sleep(2)
    print("处理完请求B")


def main():
    req_a()
    req_b()


if __name__ == '__main__':
    main()