Netty 4.1.8.Final @sharable CombinedChannelDuplexHandler usage problem demonstration

NettySharableCombinedChannelDuplexHandlerProblemDemonstration.java

import io.netty.bootstrap.Bootstrap;
import io.netty.bootstrap.ServerBootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.channel.*;
import io.netty.channel.ChannelHandler.Sharable;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.codec.ByteToMessageCodec;
import java.util.List;
import static java.lang.Integer.parseInt;

public class NettySharableCombinedChannelDuplexHandlerProblemDemonstration {

    public static void main(String[] args) throws InterruptedException {
        int port = args.length > 0 ? parseInt(args[0]) : 63889;
        initServer(port);
        Channel client1 = newClientChannel(port);
        client1.writeAndFlush("[1-1]").syncUninterruptibly();
        Channel client2 = newClientChannel(port);
        client2.writeAndFlush("[2-1]").syncUninterruptibly();
        client1.writeAndFlush("[1-2]").syncUninterruptibly();
        client2.writeAndFlush("[2-2]").syncUninterruptibly();
        client1.writeAndFlush("[1-3]").syncUninterruptibly();
        client2.writeAndFlush("[2-3]").syncUninterruptibly();
        client1.writeAndFlush("[1-4]").syncUninterruptibly();
        client2.writeAndFlush("[2-4]").syncUninterruptibly();
        Thread.sleep(100);
        System.exit(0);
    }

    static void initServer(int port) {
        ProblematicHandler problematicHandler = new ProblematicHandler();
        new ServerBootstrap()
                .group(new NioEventLoopGroup(), new NioEventLoopGroup())
                .channel(NioServerSocketChannel.class)
                .childHandler(new ChannelInitializer<SocketChannel>() {
                    protected void initChannel(SocketChannel ch) {
                        ch.pipeline()
                                .addLast("codec", new StringCodec())
                                .addLast("problematic", problematicHandler);
                    }
                })
                .bind(port)
                .syncUninterruptibly();
    }

    static Channel newClientChannel(int port) {
        return new Bootstrap()
                .group(new NioEventLoopGroup())
                .channel(NioSocketChannel.class)
                .handler(new StringCodec())
                .connect("localhost", port)
                .syncUninterruptibly()
                .channel();
    }
}

class StringCodec extends ByteToMessageCodec<String> {
    protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) {
        byte[] bytes = new byte[in.readableBytes()];
        in.readBytes(bytes);
        out.add(new String(bytes));
    }
    protected void encode(ChannelHandlerContext ctx, String msg, ByteBuf out) {
        out.writeBytes(msg.getBytes());
    }
}

@Sharable
class ProblematicHandler extends CombinedChannelDuplexHandler<ChannelInboundHandler, ChannelOutboundHandler> {
    ProblematicHandler() {
        super(
                new SimpleChannelInboundHandler<String>() {
                    protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
                        System.out.println(ctx + ": " + msg);
                    }
                },
                new ChannelOutboundHandlerAdapter());
    }
}