code: protected void notifySender(Integer xid, Xdr response) {
          ChannelFuture future = _futureMap.get(xid);
          if (future != null) {
              _responseMap.put(xid, response);
              future.setSuccess();
          }
      }
docs: Update the response map with the response and notify the thread waiting for the
  response. Do nothing if the future has been removed.
  
  @param xid
  @param response