Make a synchronous request.
        Set req.sync to True, send it to a Ryu application specified by
        req.dst, and block until receiving a reply.
        Returns the received reply.
        The argument should be an instance of EventRequestBase.

def send_request(self, req):
        """
        Make a synchronous request.
        Set req.sync to True, send it to a Ryu application specified by
        req.dst, and block until receiving a reply.
        Returns the received reply.
        The argument should be an instance of EventRequestBase.
        """

        assert isinstance(req, EventRequestBase)
        req.sync = True
        req.reply_q = hub.Queue()
        self.send_event(req.dst, req)
        # going to sleep for the reply
        return req.reply_q.get()