为什么这个异步代码不停止？

Question

以下代码片段有两个协程，分别用于服务器和客户端。客户端协程具有在 10 秒后打破 while 循环的逻辑，服务器应在 15 秒后停止。

当我运行脚本不会停止时，理想情况下，它应该在 15 秒后停止，但这并没有发生。

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

如果你运行编码你会看到这样的东西：

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

ok，client_coroutine成功完成，但是此时server_coroutine是什么状态呢？它停留在这一行 msg = yield from server_socket.recv_string() 等待从 server_socket 接收字符串的可能性，但它不会发生，因为已经没有客户端发送它！因为你的事件循环运行s 直到两个协程都完成它会永远运行。

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和一种可能的解决方法。

在现实生活中，我想你会想要做一些不同的事情：可能，为你的协程设置超时，以保证如果 client/server 停止响应它们不会永远卡住。

为什么这个异步代码不停止？

Why doesn't this async code stop?

python

coroutine

pyzmq

python-asyncio