code: def send_request(self, req):
          
  
          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()
docs: 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.