public ChannelGroupFuture close() {
      EventLoopGroup eventLoopGroup = null;
      for (Channel channel : openChannels) {
        if (channel instanceof ServerChannel) {
          eventLoopGroup = channel.eventLoop().parent();
          break;
        }
      }
      try {
        return openChannels.close();
      }
      finally {
        if (eventLoopGroup != null) {
          eventLoopGroup.shutdownGracefully(0, 15, TimeUnit.SECONDS);
        }
      }
    }
public ChannelGroupFuture close()