code: public void messageReceived(AbstractNioChannel<?> channel, ChannelEvent event) {
          boolean written = readQueue.offer(event);
          if (!written) {
              noDroppedMessages++;
              if (noDroppedMessages%10000 == 0) {
                  if (LOGGER.isInfoEnabled()) {
                      String msg = "UDP read queue full, dropping messages, consider increasing udp read queue size " +
                              "using system property " + UDP_CHANNEL_READ_QUEUE_SIZE.getPropertyName();
                      LOGGER.info(msg);
                  }
              }
          }
  
          // Wake up the selector so the event gets processed immediately by the worker thread
          if (selector != null) {
              if (wakenUp.compareAndSet(false, true)) {
                  selector.wakeup();
              }
          }
      }
docs: This method is called from the boss thread