code: @Handler(priority = -1000)
      public void onStop(Stop event) {
          if (closing || !serverSocketChannel.isOpen()) {
              return;
          }
          newSyncEventPipeline().fire(new Close(), this);
      }
docs: Shuts down the server by firing a {@link Close} using the
  server as channel. Note that this automatically results
  in closing all open connections by the runtime system
  and thus in {@link Closed} events on all subchannels.
  
  @param event the event