当客户端被物理杀死时，总是无法从服务器端关闭通道（netty）

Question

这是一个基于 netty 的 web-socket 应用。但是，当客户端在没有发送CloseWebSocketFrame 的情况下被物理杀死时，服务器需要知道通道已关闭并进行一些清理工作。 IdleStateHandler用于监控通道是否空闲。

这是通道处理程序管道。

public void initChannel(SocketChannel ch) throws Exception {
    ChannelPipeline pipeline = ch.pipeline();
    SSLEngine sslEngine = new SSLServiceBase().getSSLContext().createSSLEngine();
    sslEngine.setUseClientMode(false);
    sslEngine.setNeedClientAuth(true);
    ... // business process
    pipeline.addLast(new IdleStateHandler(30, 10, 0, TimeUnit.SECONDS));
    pipeline.addLast(new HeartbeatHandler());
}

这是HeartbeatHandler的userEventTriggered方法，用于在客户端异常关闭通道时做一些清理工作。

public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
    if (evt instanceof IdleStateEvent) {
        IdleStateEvent event = (IdleStateEvent) evt;
        if (IdleState.WRITER_IDLE.equals(event.state())) {
            ctx.writeAndFlush(new PingWebSocketFrame()).addListener(future -> {
                if (!future.isSuccess()) {
                    ChannelFuture closeFuture = ctx.channel().close();
                    if (closeFuture.isSuccess()) {
                        System.out.println("ping faild, channel close successfully");
                    } else {
                        System.out.println("ping failed, channel close failed");
                    }
                } else {
                    System.out.println("Ping succeed, keep the channel.");
                }
            });
        }
    } else {
        super.userEventTriggered(ctx, evt);
    }
}

实际上，我不断收到'close failed'，并且从服务器视图来看，该频道仍处于活动状态。谁能告诉我为什么无法关闭频道或如何关闭？非常感谢。

Answer 1

我怀疑关闭还没有完成（记住这是一个异步操作）。将代码更改为：

public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
    if (evt instanceof IdleStateEvent) {
        IdleStateEvent event = (IdleStateEvent) evt;
        if (IdleState.WRITER_IDLE.equals(event.state())) {
            ctx.writeAndFlush(new PingWebSocketFrame()).addListener(future -> { 
                if (!future.isSuccess()) {
                    ctx.close().addListener(closeFuture -> {
                        If (closeFuture.isSuccess()) {
                            System.out.println("ping faild, channel close successfully");
                        } else {
                            System.out.println("ping failed, channel close failed");
                            // TODO: You may also want to log the reason why the close operation failed. 
                            //       closeFuture.cause() will contain why.
                        }
                    });                    
                } else {
                    System.out.println("Ping succeed, keep the channel.");
                }
        });
    }
} else {
    super.userEventTriggered(ctx, evt);
}

}