为什么 sync() 在 ChannelFuture 的 netty 中不生效

Question

我正在学习Netty，我对ChannelFuture的sync方法不是很了解，这里是我的例子：

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，无论我是否为 ChannelFuture f = b.connect().sync() 删除 EchoClient.class 中的 sync()，结果始终是：啊啊 8811绑定成功

在我看来，如果我加上sync()，结果应该是： 8811 绑定成功 aaa

因为主线程将等待通道连接，

如果我去掉sync()，结果应该是：啊啊 8811绑定成功

因为 connect() 是异步的

为什么我错了？

Answer 1

一旦操作完成，sync() 将解除阻塞，然后 EventLoop 将通知所有附加的侦听器到 ChannelFuture。由于您的主线程和 EventLoop 线程不同，因此您很有可能会在 ChannelFutureListener[=16= 之前看到主线程中的 System.out.println(...) ]

为什么 sync() 在 ChannelFuture 的 netty 中不生效

why sync() not take effect in netty for ChannelFuture

java

netty