为什么sync()在频道未来的netty中不生效

Question

我正在学习Netty，我不太了解ChannelFuture的同步方法，这是我的示例：

public class EchoServer {
    private final int port;

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

    public static void main(String[] args) throws Exception {
        if (args.length != 1) {
            System.err.println("Usage: " + EchoServer.class.getSimpleName() + " <port>");
            return;
        }

        int port = Integer.parseInt(args[0]);

        new EchoServer(port).start();
    }

    public void start() throws Exception {
        // final EchoServerHandler serverHandler = new EchoServerHandler();
        EventLoopGroup group = new NioEventLoopGroup();

        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(group).channel(NioServerSocketChannel.class).localAddress(new InetSocketAddress(port)).childHandler(new ChannelInitializer<SocketChannel>() {

                @Override
                protected void initChannel(SocketChannel ch) throws Exception {
                    // ch.pipeline().addLast(serverHandler);
                }
            });

            ChannelFuture f = b.bind().sync();
            f.channel().closeFuture().sync();
        } finally {
            group.shutdownGracefully().sync();
        }
    }
}



public class EchoClient {
    private final String host;
    private final int port;

    public EchoClient(String host, int port) {
        this.host = host;
        this.port = port;
    }

    public void start() throws Exception {
        EventLoopGroup group = new NioEventLoopGroup();

        try {
            Bootstrap b = new Bootstrap();
            b.group(group).channel(NioSocketChannel.class).remoteAddress(new InetSocketAddress(host, port)).handler(new ChannelInitializer<SocketChannel>() {

                @Override
                protected void initChannel(SocketChannel ch) throws Exception {
                    // ch.pipeline().addLast(new EchoClientHandler());
                }
            });


            ChannelFuture f = b.connect().sync().addListener(future -> {

                   if(future.isSuccess()) {

                       System.out.println(port + " bind success");

                   } else{

                       System.err.println(port + " bind fail");

                   }

               });

            System.out.println("aaa");

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

    public static void main(String[] args) throws Exception {
        if (args.length != 2) {
            System.err.println("Usage: " + EchoClient.class.getSimpleName() + " <host> <port>");
            return;
        }

        String host = args[0];
        int port = Integer.parseInt(args[1]);

        new EchoClient(host, port).start();
    }
}

我的问题是，无论我在EchoClient中删除了什么sync（）。ChannelFuture的类f=b.connect（）。无论是否为sync（），结果总是：aaa 8811 bind success

在我看来，如果添加sync（），结果应该是：8811 bind success aaa

由于主线程会等待通道连接，

如果我删除 sync（），结果应该是：aaa 8811 绑定成功

由于connect（）是异步的

为什么我错了？

Answer 1

sync（）将在操作完成后立即解除屏蔽，然后EventLoop将通知所有附加的监听器到ChannelFuture。由于您的主线程和EventLoop线程是不同的，因此您很有可能会在ChannelFutureListener中之前在主线程中看到System.out.println（…）