python - 获取一个异步服务器来调用另一个服务器

Question

所以我修改了 asyncio 客户端和服务器的示例(可在此处找到:https://docs.python.org/3/library/asyncio-protocol.html#protocol-example-tcp-echo-server-and-client)，我只想让 client.py 调用 serverone.py，然后调用 servertwo.py。

客户端.py

#!/usr/bin/env python3.4
import asyncio

class EchoClient(asyncio.Protocol):
    message = 'This is the Client'

    def connection_made(self, transport):
        transport.write(self.message.encode())

    def data_received(self, data):
        print('data received: {}'.format(data.decode()))

    def connection_lost(self, exc):
        asyncio.get_event_loop().stop()

loop = asyncio.get_event_loop()
coro = loop.create_connection(EchoClient, '127.0.0.1', 8888)
loop.run_until_complete(coro)
loop.run_forever()
loop.close()

serverone.py

#!/usr/bin/env python3.4

import asyncio

class EchoClient(asyncio.Protocol):
    message = 'Server One sending message'

    def connection_made(self, transport):
        transport.write(self.message.encode())

    def data_received(self, data):
        print('data received: {}'.format(data.decode()))

    def connection_lost(self, exc):
        asyncio.get_event_loop().stop()

class EchoServer(asyncio.Protocol):
    def connection_made(self, transport):
        peername = transport.get_extra_info('peername')
        self.transport = transport

    def data_received(self, data):
        loop = asyncio.get_event_loop()
        coro = loop.create_connection(EchoClient, '127.0.0.1', 8889)
        loop.run_until_complete(coro)
        # close the socket
        self.transport.close()
        loop.close()

loop = asyncio.get_event_loop()
coro = loop.create_server(EchoServer, '127.0.0.1', 8888)
server = loop.run_until_complete(coro)
try:
    loop.run_forever()
except KeyboardInterrupt:
    print("exit")
finally:
    server.close()
    loop.close()

servertwo.py

#!/usr/bin/env python3.4

import asyncio

class EchoServer(asyncio.Protocol):
    def connection_made(self, transport):
        peername = transport.get_extra_info('peername')
        self.transport = transport

    def data_received(self, data):
        print('data received: {}'.format(data.decode()))
        self.transport.write(data)
        # close the socket
        self.transport.close()

loop = asyncio.get_event_loop()
coro = loop.create_server(EchoServer, '127.0.0.1', 8889)
server = loop.run_until_complete(coro)
try:
    loop.run_forever()
except KeyboardInterrupt:
    print("exit")
finally:
    server.close()
    loop.close()

我在终端中启动 servertwo.py 和 serverone.py，然后调用 client.py。部分工作；客户端确实调用了 serverone，而 serverone 确实调用了 servertwo，但随后 serverone 失败并出现此错误:

Exception in callback <bound method _SelectorSocketTransport._read_ready of <asyncio.selector_events._SelectorSocketTransport object at 0x7fbf4453b048>>()
handle: Handle(<bound method _SelectorSocketTransport._read_ready of <asyncio.selector_events._SelectorSocketTransport object at 0x7fbf4453b048>>, ())
Traceback (most recent call last):
  File "/usr/lib64/python3.4/asyncio/events.py", line 39, in _run
    self._callback(*self._args)
  File "/usr/lib64/python3.4/asyncio/selector_events.py", line 458, in _read_ready
    self._protocol.data_received(data)
  File "./serverone.py", line 25, in data_received
    loop.run_until_complete(coro)
  File "/usr/lib64/python3.4/asyncio/base_events.py", line 203, in run_until_complete
    self.run_forever()
  File "/usr/lib64/python3.4/asyncio/base_events.py", line 179, in run_forever
    raise RuntimeError('Event loop is running.')
RuntimeError: Event loop is running.

文档没有涵盖很多奇怪的用例，所以我有点卡住了。我应该使用 asyncio.async 来调用电话吗？我是否正确地处理了问题？

如何修复或避免 RuntimeError？

Answer 1

您可以使用 asyncio.async安排 create_connection 返回的协程由事件循环运行，然后使用 asyncio.Future 的 add_done_callback 方法(更具体地说, 一个 asyncio.Task )，一旦协程完成，async 返回以关闭循环:

class EchoServer(asyncio.Protocol):
    def connection_made(self, transport):
        peername = transport.get_extra_info('peername')
        self.transport = transport

    def data_received(self, data):
        loop = asyncio.get_event_loop()
        coro = loop.create_connection(EchoClient, '127.0.0.1', 8890)
        fut = asyncio.async(coro)
        fut.add_done_callback(self.shutdown)

    def shutdown(self, *args):
        self.transport.close()
        loop.stop()