Question

稍微修改了以下代码

import asyncio
asyncio.tasks._DEBUG = True


class EchoServer(asyncio.Protocol):
    def connection_made(self, transport):
        name = transport.get_extra_info('sockname')
        peername = transport.get_extra_info('peername')
        print('Connection:',name,'<--',peername)
        self.transport = transport

    def data_received(self, data):
        name = self.transport.get_extra_info('sockname')
        peername = self.transport.get_extra_info('peername')

        print('Got data:',name,'<--',peername,':',data.decode() )
        if name[1] == 8888:
            print("Making connection")
            reader, writer = yield from asyncio.open_connection('127.0.0.1', 8889, loop=asyncio.get_event_loop())
        else:
            self.transport.write(data)

        self.transport.close()


loop = asyncio.get_event_loop()
coro_1 = loop.create_server(EchoServer, '127.0.0.1', 8888)
coro_2 = loop.create_server(EchoServer, '127.0.0.1', 8889)
server_1 = loop.run_until_complete(coro_1)
server_2 = loop.run_until_complete(coro_2)
print('Serving on {}'.format(server_1.sockets[0].getsockname()))
print('Serving on {}'.format(server_2.sockets[0].getsockname()))

try:
    loop.run_forever()
except KeyboardInterrupt:
    print("^C caught, exiting")
finally:
    server_1.close()
    server_2.close()
    loop.close()

然而，当我运行它时，它甚至似乎运行 data_received函数：

Serving on ('127.0.0.1', 8888)
Serving on ('127.0.0.1', 8889)
Connection: ('127.0.0.1', 8888) <-- ('127.0.0.1', 36580)

但是当我注释掉yield from行时，它会以我期望的方式运行。

Serving on ('127.0.0.1', 8888)
Serving on ('127.0.0.1', 8889)
Connection: ('127.0.0.1', 8888) <-- ('127.0.0.1', 36581)
Got data: ('127.0.0.1', 8888) <-- ('127.0.0.1', 36581) : Hi, gaise!
Making connection

我尝试添加：

@asyncio.coroutine
def do_a_thing():
    print("hey, it's a thing!")

def try_stuff():
    print('Trying')
    yield from asyncio.async(do_a_thing())

并改为调用try_stuff。这会输出“正在建立连接”，但不会输出“正在尝试”。通过将yield from行更改为简单的调用，输出'Trying'。如果我从do_a_thing删除协程装饰器，那么我得到输出。

对我来说重要的是我正在尝试创建与第二台服务器的异步连接。但显然，yield from的存在阻止了任何进一步的处理（至少我可以告诉它 - 它肯定会因打印而停止）。

那么我做错了什么，我该如何解决这个问题呢？

Answer 1

yield from 必须才能在协程中使用。正如我所看到的，data_received因为一些asyncio内部结构而不能成为协同程序。

解决方案是将代码包装在协程中并使用asyncio.Task（）调用它。

作为示例，您可以查看我的experiments

Answer 2

正如gawel所提到的，yield from必须在协程中使用，尽管Server类在某些asyncio调用中，但这些函数并不是神奇的协同程序。

EchoServer需要看起来像这样：

class EchoServer(asyncio.Protocol):
    def connection_made(self, transport):
        name = transport.get_extra_info('sockname')
        peername = transport.get_extra_info('peername')
        print('Connection:',name,'<--',peername)
        self.transport = transport

    # This is where the magic happens
    @asyncio.coroutine
    def send_data(self, data):
        print("Making connection")
        reader, writer = yield from asyncio.open_connection('127.0.0.1', 8889)
        print("Connection made")
        writer.write(data)
        print("Data sent")
        # For some reason, not providing n caused this to not return anything
        resp = yield from reader.read(1024)
        print("Got response")
        self.transport.write(resp)
        print('Data returned:',resp)

    def data_received(self, data):
        name = self.transport.get_extra_info('sockname')
        peername = self.transport.get_extra_info('peername')

        print('Got data:',name,'<--',peername,':',data.decode() )
        if name[1] == 8888:
            print("making task")
            asyncio.Task(self.send_data(data))
            print("done making task")
        else:
            print("Sending response")
            self.transport.write(data[::-1])

为什么asyncio.open_connection（或任何其他协同程序）阻止data_received处理？

2 个答案: