如何一次向tornado套接字客户端广播消息？

import tornado.websocket

class BroadcastHandler(tornado.websocket.WebSocketHandler):
    clients = set()

    def open(self):
        BroadcastHandler.clients.add(self)

    def on_message(self, message):
        # 接收到消息时，广播给所有连接的客户端
        for client in BroadcastHandler.clients:
            client.write_message(message)

    def on_close(self):
        BroadcastHandler.clients.remove(self)

import tornado.web

app = tornado.web.Application([
    (r'/broadcast', BroadcastHandler),
])

if __name__ == '__main__':
    app.listen(8888)
    tornado.ioloop.IOLoop.current().start()