Netty答疑解惑-EventLoopGroup自定义Executor线程数小于参数nThreads会怎么样?

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1. 引言

Java中网络开发Netty肯定绕不开，之前在研究Netty源码过程中发现当你创建 EventLoopGroup的时候可以自定义执行器，环境话说就是可以用Jdk实现的执行器也就是通常所说的线程池。其中有这样的一个构造函数：

public NioEventLoopGroup(int nThreads, Executor executor) {
    this(nThreads, executor, SelectorProvider.provider());
}
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nThreads：表示EventLoopGroup线程数量
executor：表示用户自定义的执行器

执行器我们用JDK实现的线程池作为执行器。

问题：当nThreads的值大于线程池中线程的最大数会怎么样？

下面就通过代码来看一下这种问题下会发生什么，同时应该怎么去解决这个问题。

2. 案例代码

服务端代码

public class DiscardServer {
    private int port;

    public DiscardServer(int port) {
        this.port = port;
    }

    public void run() throws Exception {
        EventLoopGroup bossGroup = new NioEventLoopGroup(1); // (1)
        EventLoopGroup workerGroup = new NioEventLoopGroup(3, Executors.newFixedThreadPool(2, new ThreadFactory() {
            private AtomicInteger threadNumber = new AtomicInteger();
            @Override
            public Thread newThread(Runnable r) {
                return new Thread(r, "Thread-mxsm-"+threadNumber.incrementAndGet());
            }
        }));
        try {
            ServerBootstrap b = new ServerBootstrap(); // (2)
            b.group(bossGroup, workerGroup)
                .channel(NioServerSocketChannel.class) // (3)
                .childHandler(new ChannelInitializer<SocketChannel>() { // (4)
                    @Override
                    public void initChannel(SocketChannel ch) throws Exception {
                        ch.pipeline().addLast(new TimeServerInHandler());
                    }
                })
                .option(ChannelOption.SO_BACKLOG, 128)          // (5)
                .childOption(ChannelOption.SO_KEEPALIVE, true); // (6)
            ChannelFuture f = b.bind(port).sync(); // (7)
            f.channel().closeFuture().sync();
        } finally {
            workerGroup.shutdownGracefully();
            bossGroup.shutdownGracefully();
        }
    }

    public static void main(String[] args) throws Exception {
        int port = 8080;
        if (args.length > 0) {
            port = Integer.parseInt(args[0]);
        }
        new DiscardServer(port).run();
    }
}

@Sharable
public class TimeServerInHandler extends ChannelInboundHandlerAdapter {
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        System.out.println(this.getClass().getSimpleName()+"--channelRead");
        final ByteBuf time = ctx.alloc().buffer(4); // (2)
        time.writeInt((int) (System.currentTimeMillis() / 1000L + 2208988800L));
        ctx.writeAndFlush(time); // (3)
    }
}
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客户端代码：

public class TimeClient {
    public static void main(String[] args) throws Exception {

        for(int i = 0; i < 100; ++i){
            new Thread(new Runnable(){
                @Override
                public void run() {
                    try {
                        new TimeClient().test();
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            }).start();
        }

    }

    public  void test() throws Exception{
        String host = "127.0.0.1";
        int port = Integer.parseInt("8080");
        EventLoopGroup workerGroup = new NioEventLoopGroup();

        try {
            Bootstrap b = new Bootstrap(); // (1)
            b.group(workerGroup); // (2)
            b.channel(NioSocketChannel.class); // (3)
            b.option(ChannelOption.SO_KEEPALIVE, true); // (4)
            b.handler(new ChannelInitializer<SocketChannel>() {
                @Override
                public void initChannel(SocketChannel ch) throws Exception {
                    // ch.pipeline().addLast(new TimeClientOutHandler());
                    ch.pipeline().addLast(new TimeClientInHandler());
                }
            });

            // Start the client.
            ChannelFuture f = b.connect(host, port).sync(); // (5)
            ByteBuf byteBuf = Unpooled.buffer();
            // Wait until the connection is closed.
            byteBuf.writeBytes("1111".getBytes(StandardCharsets.UTF_8));
            f.channel().writeAndFlush(byteBuf);

            f.channel().closeFuture().sync();
        } finally {
            workerGroup.shutdownGracefully();
        }
    }
}

public class TimeClientInHandler extends ChannelInboundHandlerAdapter {

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) {
        System.out.println(this.getClass().getSimpleName()+"--channelRead");
        ByteBuf m = (ByteBuf) msg; // (1)
        try {
            long currentTimeMillis = (m.readUnsignedInt() - 2208988800L) * 1000L;
            System.out.println(new Date(currentTimeMillis));
            //ctx.close();
        } finally {
            m.release();
        }
    }
    
}
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