为什么客户端被SIGKILL杀死时在服务器上调用channelInactive？

Question

[有一个回显服务器和一个回显客户端。当我使用kill -9 <client_pid>杀死客户端进程时，将调用服务器上的channelInactive。

客户端被SIGKILL杀死，因此应该没有时间主动关闭此套接字。结果，不应触发服务器上的channelInactive，这确实发生了。

为什么当客户端被channelInactive杀死时在服务器上调用SIGKILL？

EchoServer类

public class EchoServer {
  private final int port;

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

  public static void main(String[] args) throws InterruptedException {
    int port = 9001;
    new EchoServer(port).start();
  }

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

    try {
      ServerBootstrap bootstrap = new ServerBootstrap();
      bootstrap
          .group(group)
          .channel(NioServerSocketChannel.class)
          .childHandler(new ChannelInitializer<SocketChannel>() {
            @Override
            protected void initChannel(SocketChannel ch) throws Exception {
              ch.pipeline()
                .addLast(new ChannelInboundHandlerAdapter() {
                  @Override
                  public void channelInactive(ChannelHandlerContext ctx) throws Exception {
                    System.out.println("channelInactive()");
                  }
                });
            }
          });

      ChannelFuture future = bootstrap.bind(new InetSocketAddress(port)).sync();
      future.channel().closeFuture().sync();
    } finally {
      group.shutdownGracefully().sync();
    }
  }
}

EchoClient类

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 InterruptedException {
    EventLoopGroup group = new NioEventLoopGroup();
    try {
      Bootstrap bootstrap = new Bootstrap();
      bootstrap
          .group(group)
          .channel(NioSocketChannel.class)
          .handler(new ChannelInitializer<SocketChannel>() {
            @Override
            protected void initChannel(SocketChannel ch) throws Exception {
            }
          });

      ChannelFuture future = bootstrap.connect(new InetSocketAddress(host, port)).sync();
      future.channel().closeFuture().sync();
    } finally {
      group.shutdownGracefully().sync();
    }
  }

  public static void main(String[] args) throws InterruptedException {
    new EchoClient("localhost", 9001).start();
  }
}

Answer 1

客户端被SIGKILL杀死，因此它应该没有时间主动关闭此套接字。

客户端应用程序未主动关闭套接字。如果不再有本地应用程序打开，则客户端OS内核会隐式关闭套接字。