在Tornado中的阻塞上下文中调用异步函数

Question

我想在Tornado框架中实现一个基于web套接字的服务。当用户关闭web套接字时，我想通知其他用户这一点。然而，on_close显然是一个阻塞函数，而我的_broadcast(str) -> None函数是异步的

我怎样才能调用这个函数呢

from tornado import websocket

logging.basicConfig(level=logging.INFO)
logger = logging.getLogger(__name__)


class SocketHandler(websocket.WebSocketHandler):
    async def open(self, *args, conns, **kwargs):
        logger.info(f"Opened a new connection to client {id(self)}")
        self._conns = conns

    async def on_message(self, message):
        logger.info(f"Client {id(self)} sent message: {message}")
        await self._broadcast(message)

    def on_close(self):
        logger.info(f"Client {id(self)} has left the scene")
        self._conns.remove(self)
        self._broadcast("something")  # TODO

    async def _broadcast(self, msg): 
        for conn in self._conns: 
            try:
                await conn.write_message(msg)
            except websocket.WebSocketClosedError:
                pass


app = web.Application([
    (r'/ws', SocketHandler)
])

if __name__ == '__main__':
    app.listen(9000)
    ioloop.IOLoop.instance().start()

Answer 1

我认为使用asyncio.Queue的解决方案应该适合您

我制作了一个小班作为一个模型来测试这一点：

import asyncio
import time


class Thing:
    on_close_q = asyncio.Queue()

    def __init__(self):
        self.conns = range(3)

    def on_close(self, id):
        time.sleep(id)
        print(f'closing {id}')
        self.on_close_q.put_nowait((self, id))

    async def notify(self, msg):
        print('in notify')
        for conn in range(3):
            print(f'notifying {conn} {msg}')


async def monitor_on_close():
    print('monitoring')
    while True:
        instance, id = await Thing.on_close_q.get()
        await instance.notify(f'{id} is closed')

从那里开始，您需要在从tornado获得的ioloop中运行monitor_on_close。我从未使用过tornado，但我认为在__main__块中添加类似的内容应该可以：

    ioloop.IOLoop.current().add_callback(monitor_on_close)