A Netty 4 ChannelOutboundHandler that implements a queue system to optimize usage and throughput

WriteQueueOutboundChannelHandler.java

import io.netty.channel.*;

import java.util.Queue;
import java.util.concurrent.ConcurrentLinkedQueue;

public class WriteQueueOutboundChannelHandler extends ChannelOutboundHandlerAdapter {
    private static final int QUEUE_SIZE_WARNING = 5000;
    private ChannelHandlerContext ctx;
    private final Queue<Object> messageQueue = new ConcurrentLinkedQueue<>();
    private int qSize = 0; //should make access synchronized
    private boolean isWriting;

    private final ChannelFutureListener sendListener = new ChannelFutureListener() {
        @Override
        public void operationComplete(ChannelFuture future) {
            if (future.isSuccess()) {
                ctx.fireUserEventTriggered("WRITE_MESSAGE_COMPLETE"); //might want to do a message counter in another handler
                poll();
            } else {
                future.channel().close();
                messageQueue.clear();
            }
        }
    };
    private void poll() {
        isWriting = true;
        if (!messageQueue.isEmpty()) {
            this.ctx.writeAndFlush(messageQueue.poll()).addListener(sendListener);
            qSize--;
        }
        else {
            isWriting = false;
        }
    }

    @Override
    public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {
        this.ctx = ctx;
        int size = qSize;
        if (size > QUEUE_SIZE_WARNING) {
            System.out.println("Queue size: "+size); //should handle somehow
        }
        messageQueue.offer(msg);
        qSize++;
        if (!isWriting) {
            poll();
        }
    }
}

This class seeks to address Netty 4 issue 1759.