How to use the discover.broadcast_offline function in discover

def shutdown():
    log.info('Stopping http server')

    broadcast_offline()

    # 关闭本进程所有的客户端连接并将用户从在线列表中去掉。
    log.info('make all user offline')
    try:
        WebSocketHandler.shutdown()
    except Exception, e:
        log.error(e, exc_info=True)

    log.info('Will shutdown in %s seconds ...',
             MAX_WAIT_SECONDS_BEFORE_SHUTDOWN)
    io_loop = tornado.ioloop.IOLoop.instance()
    deadline = time.time() + MAX_WAIT_SECONDS_BEFORE_SHUTDOWN

    def stop_loop():
        now = time.time()
        if now < deadline and (io_loop._callbacks or io_loop._timeouts):