Java、Netty、TCP和UDP连接集成 : No buffer space available for UDP connection

Question

我有使用 TCP 和 UDP 协议(protocol)的应用程序。主要假设是客户端通过 TCP 协议(protocol)连接到服务器，当连接建立时，正在发送 UDP 数据报。我必须支持两种连接服务器的场景: - 服务器运行时客户端连接 - 当服务器关闭时客户端连接并重试连接直到服务器再次启动

对于第一个场景，一切都工作得很好:我已经工作了两个连接。问题出在第二种情况。当客户端尝试几次通过 TCP 连接并最终连接时，UDP 连接函数会抛出异常:

java.net.SocketException: No buffer space available (maximum connections reached?): bind
at sun.nio.ch.Net.bind0(Native Method)
at sun.nio.ch.Net.bind(Net.java:344)
at sun.nio.ch.DatagramChannelImpl.bind(DatagramChannelImpl.java:684)
at sun.nio.ch.DatagramSocketAdaptor.bind(DatagramSocketAdaptor.java:91)
at io.netty.channel.socket.nio.NioDatagramChannel.doBind(NioDatagramChannel.java:192)
at io.netty.channel.AbstractChannel$AbstractUnsafe.bind(AbstractChannel.java:484)
at io.netty.channel.DefaultChannelPipeline$HeadContext.bind(DefaultChannelPipeline.java:1080)
at io.netty.channel.AbstractChannelHandlerContext.invokeBind(AbstractChannelHandlerContext.java:430)
at io.netty.channel.AbstractChannelHandlerContext.bind(AbstractChannelHandlerContext.java:415)
at io.netty.channel.DefaultChannelPipeline.bind(DefaultChannelPipeline.java:903)
at io.netty.channel.AbstractChannel.bind(AbstractChannel.java:197)
at io.netty.bootstrap.AbstractBootstrap$2.run(AbstractBootstrap.java:350)
at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:380)
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:357)
at io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:116)
at io.netty.util.concurrent.DefaultThreadFactory$DefaultRunnableDecorator.run(DefaultThreadFactory.java:137)
at java.lang.Thread.run(Thread.java:722)

当我重新启动客户端应用程序而不对服务器执行任何操作时，客户端连接时将出现任何问题。

什么会导致问题？

下面我附上了类的源代码。所有源代码均来自 Netty 官方项目页面中的示例。我唯一修改的是用非静态变量和函数替换了静态变量和函数。这是因为将来我需要许多 TCP-UDP 连接到多个服务器。

public final class UptimeClient {
static final String HOST = System.getProperty("host", "192.168.2.193");
static final int PORT = Integer.parseInt(System.getProperty("port", "2011"));
static final int RECONNECT_DELAY = Integer.parseInt(System.getProperty("reconnectDelay", "5"));
static final int READ_TIMEOUT = Integer.parseInt(System.getProperty("readTimeout", "10"));

private static UptimeClientHandler handler;

public void runClient() throws Exception {
    configureBootstrap(new Bootstrap()).connect();
}

private Bootstrap configureBootstrap(Bootstrap b) {
    return configureBootstrap(b, new NioEventLoopGroup());
}

@Override
protected Object clone() throws CloneNotSupportedException {
    return super.clone(); //To change body of generated methods, choose Tools | Templates.
}

Bootstrap configureBootstrap(Bootstrap b, EventLoopGroup g) {
    if(handler == null){
            handler = new UptimeClientHandler(this);
    }
    b.group(g)
     .channel(NioSocketChannel.class)
     .remoteAddress(HOST, PORT)
     .handler(new ChannelInitializer<SocketChannel>() {
        @Override
        public void initChannel(SocketChannel ch) throws Exception {
            ch.pipeline().addLast(new IdleStateHandler(READ_TIMEOUT, 0, 0), handler);
        }
     });

    return b;
}

void connect(Bootstrap b) {
    b.connect().addListener(new ChannelFutureListener() {
        @Override
        public void operationComplete(ChannelFuture future) throws Exception {
            if (future.cause() != null) {
                handler.startTime = -1;
                handler.println("Failed to connect: " + future.cause());
            }
        }
    });
}
}


@Sharable
public class UptimeClientHandler extends SimpleChannelInboundHandler<Object> {
UptimeClient client;
public UptimeClientHandler(UptimeClient client){
    this.client = client;
}
long startTime = -1;

@Override
public void channelActive(ChannelHandlerContext ctx) {
    try {
        if (startTime < 0) {
            startTime = System.currentTimeMillis();
        }
        println("Connected to: " + ctx.channel().remoteAddress());
        new QuoteOfTheMomentClient(null).run();
    } catch (Exception ex) {
        Logger.getLogger(UptimeClientHandler.class.getName()).log(Level.SEVERE, null, ex);
    }
}

@Override
public void channelRead0(ChannelHandlerContext ctx, Object msg) throws Exception {
}

@Override
public void userEventTriggered(ChannelHandlerContext ctx, Object evt) {
    if (!(evt instanceof IdleStateEvent)) {
        return;
    }

    IdleStateEvent e = (IdleStateEvent) evt;
    if (e.state() == IdleState.READER_IDLE) {
        // The connection was OK but there was no traffic for last period.
        println("Disconnecting due to no inbound traffic");
        ctx.close();
    }
}

@Override
public void channelInactive(final ChannelHandlerContext ctx) {
    println("Disconnected from: " + ctx.channel().remoteAddress());
}

@Override
public void channelUnregistered(final ChannelHandlerContext ctx) throws Exception {
    println("Sleeping for: " + UptimeClient.RECONNECT_DELAY + 's');

    final EventLoop loop = ctx.channel().eventLoop();
    loop.schedule(new Runnable() {
        @Override
        public void run() {
            println("Reconnecting to: " + UptimeClient.HOST + ':' + UptimeClient.PORT);
            client.connect(client.configureBootstrap(new Bootstrap(), loop));
        }
    }, UptimeClient.RECONNECT_DELAY, TimeUnit.SECONDS);
}

@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
    cause.printStackTrace();
    ctx.close();
}

void println(String msg) {
    if (startTime < 0) {
        System.err.format("[SERVER IS DOWN] %s%n", msg);
    } else {
        System.err.format("[UPTIME: %5ds] %s%n", (System.currentTimeMillis() - startTime) / 1000, msg);
    }
    }
}

public final class QuoteOfTheMomentClient {

private ServerData config;
public QuoteOfTheMomentClient(ServerData config){
    this.config = config;
}

public void run() throws Exception {


    EventLoopGroup group = new NioEventLoopGroup();
    try {
        Bootstrap b = new Bootstrap();
        b.group(group)
         .channel(NioDatagramChannel.class)
         .option(ChannelOption.SO_BROADCAST, true)
         .handler(new QuoteOfTheMomentClientHandler());

        Channel ch = b.bind(0).sync().channel();

        ch.writeAndFlush(new DatagramPacket(
                Unpooled.copiedBuffer("QOTM?", CharsetUtil.UTF_8),
                new InetSocketAddress("192.168.2.193", 8193))).sync();

        if (!ch.closeFuture().await(5000)) {
            System.err.println("QOTM request timed out.");
        }
    }
    catch(Exception ex)
    {
        ex.printStackTrace();
    }
    finally {
        group.shutdownGracefully();
    }
    }
}

public class QuoteOfTheMomentClientHandler extends SimpleChannelInboundHandler<DatagramPacket> {

@Override
public void channelRead0(ChannelHandlerContext ctx, DatagramPacket msg) throws Exception {
    String response = msg.content().toString(CharsetUtil.UTF_8);
    if (response.startsWith("QOTM: ")) {
        System.out.println("Quote of the Moment: " + response.substring(6));
        ctx.close();
    }
}

@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
    cause.printStackTrace();
    ctx.close();
    }
}

Answer 1

如果您的服务器是 Windows Server 2008(R2 或 R2 SP1)，则 this stackoverflow answer 可能描述并解决了此问题。指的是 Microsoft KB article #2577795

This issue occurs because of a race condition in the Ancillary Function Driver for WinSock (Afd.sys) that causes sockets to be leaked. With time, the issue that is described in the "Symptoms" section occurs if all available socket resources are exhausted.

<小时/>

如果您的服务器是 Windows Server 2003，则 this stackoverflow answer 可能描述并解决了此问题。指的是 Microsoft KB article #196271

The default maximum number of ephemeral TCP ports is 5000 in the products that are included in the "Applies to" section. A new parameter has been added in these products. To increase the maximum number of ephemeral ports, follow these steps...

...这基本上意味着您已经用完了临时端口。