为什么异步代码没有停止？

Question

以下代码段分别具有两个协程，分别用于服务器和客户端。 客户端协程具有在10秒后中断while循环的逻辑，服务器应在15秒后停止。

当我运行脚本时，它不会停止，理想情况下，它应该在15秒后停止，但这不会发生。

import asyncio
import time
import zmq
import zmq.asyncio

zmq.asyncio.install()

ctx = zmq.asyncio.Context()


server_socket = ctx.socket(zmq.REP)
client_socket = ctx.socket(zmq.REQ)

server_socket.bind("tcp://127.0.0.1:8899")
client_socket.connect("tcp://127.0.0.1:8899")

t0 = time.time()


@asyncio.coroutine
def server_coroutine():

    while True:
        msg = yield from server_socket.recv_string()
        print(msg)
        msg = "Server:: {}".format(msg)
        yield from server_socket.send_string(msg)
        t1 = time.time()
        elapsed_time = t1 - t0
        # print('elapsed time is {}'.format(elapsed_time))
        if elapsed_time > 15:
            print("Breaking Server loop")
            break

@asyncio.coroutine
def client_coroutine():
    counter = 0
    while True:
        yield from asyncio.sleep(2)
        msg = 'Message: {}'.format(counter)
        yield from client_socket.send_string(msg)
        res = yield from client_socket.recv_string()
        print(res)
        t1 = time.time()
        elapsed_time = t1 - t0
        print('elapsed time is {}'.format(elapsed_time))
        if elapsed_time > 10:
            print("Breaking Client loop")
            break
        counter += 1


if __name__ == '__main__':

    loop = asyncio.get_event_loop()

    loop.run_until_complete(asyncio.gather(
        asyncio.ensure_future(server_coroutine()),
        asyncio.ensure_future(client_coroutine())
    ))

Answer 1

如果您运行代码，您将看到类似以下内容：

Server:: Message: 4
elapsed time is 10.022311687469482
Breaking Client loop

好的， client_coroutine成功完成，但是此时server_coroutine处于什么状态？ 它停留在此行msg = yield from server_socket.recv_string()等待从server_socket字符串的可能性，但是不会发生，因为已经没有客户端可以发送它了！ 而且由于您的事件循环一直运行到两个协程完成，所以它将永远运行。

这是最简单的解决方法：

@asyncio.coroutine
def server_coroutine():
    while True:
        msg = yield from server_socket.recv_string()
        if msg == 'CLOSE':  # LOOK HERE 1
            break
        print(msg)
        msg = "Server:: {}".format(msg)
        yield from server_socket.send_string(msg)
        t1 = time.time()
        elapsed_time = t1 - t0
        # print('elapsed time is {}'.format(elapsed_time))
        if elapsed_time > 15:
            print("Breaking Server loop")
            break

@asyncio.coroutine
def client_coroutine():
    counter = 0
    while True:
        yield from asyncio.sleep(2)
        msg = 'Message: {}'.format(counter)
        yield from client_socket.send_string(msg)
        res = yield from client_socket.recv_string()
        print(res)
        t1 = time.time()
        elapsed_time = t1 - t0
        print('elapsed time is {}'.format(elapsed_time))
        if elapsed_time > 10:
            print("Breaking Client loop")
            yield from client_socket.send_string('CLOSE')  # LOOK HERE 2
            break
        counter += 1

请注意，此修复程序仅用于演示问题以及解决该问题的一种可能方法。

在现实生活中，我认为您可能会想做一些不同的事情：可能会为协程设置超时，以确保如果客户端/服务器停止响应，协程不会永远卡住。