将 75 个客户端连接到服务器后连接被拒绝

Question

>我使用以下代码开发了一个服务器通道套接字：

public class EchoServer {
private static final int BUFFER_SIZE = 1024;
private final static int DEFAULT_PORT = 9090;
private long numMessages = 0;
private long loopTime;
private InetAddress hostAddress = null;
private int port;
private Selector selector;
// The buffer into which we'll read data when it's available
private ByteBuffer readBuffer = ByteBuffer.allocate(BUFFER_SIZE);
int timestamp=0;
public EchoServer() throws IOException {
    this(DEFAULT_PORT);
}
public EchoServer(int port) throws IOException {
    this.port = port;
    hostAddress = InetAddress.getByName("127.0.0.1");
    selector = initSelector();
    loop();
}
private Selector initSelector() throws IOException {
    Selector socketSelector = SelectorProvider.provider().openSelector();
    ServerSocketChannel serverChannel = ServerSocketChannel.open();
    serverChannel.configureBlocking(false);
    InetSocketAddress isa = new InetSocketAddress(hostAddress, port);
    serverChannel.socket().bind(isa);
    serverChannel.register(socketSelector, SelectionKey.OP_ACCEPT);
    return socketSelector;
}
private void loop() {
    for (;true;) {
        try {
            selector.select();
            Iterator<SelectionKey> selectedKeys = selector.selectedKeys()
                    .iterator();
            while (selectedKeys.hasNext()) {
                SelectionKey key = selectedKeys.next();
                selectedKeys.remove();
                if (!key.isValid()) {
                    continue;
                }
                 // Check what event is available and deal with it
                if (key.isAcceptable()) {
                    accept(key);
                } else if (key.isWritable()) {
                    write(key);
                }
            }
            Thread.sleep(3000);
            timestamp+=3;
        } catch (Exception e) {
            e.printStackTrace();
            System.exit(1);
        }

    }
}
private void accept(SelectionKey key) throws IOException {
    ServerSocketChannel serverSocketChannel = (ServerSocketChannel) key.channel();
    SocketChannel socketChannel = serverSocketChannel.accept();
    socketChannel.configureBlocking(false);
    socketChannel.setOption(StandardSocketOptions.SO_KEEPALIVE, true);
    socketChannel.setOption(StandardSocketOptions.TCP_NODELAY, true);
  //  socketChannel.register(selector, SelectionKey.OP_READ);
    socketChannel.register(selector, SelectionKey.OP_WRITE);
    System.out.println("Client is connected");
}
private void write(SelectionKey key) throws IOException {
    SocketChannel socketChannel = (SocketChannel) key.channel();
    ByteBuffer dummyResponse = ByteBuffer.wrap(("ok:" + String.valueOf(timestamp)) .getBytes("UTF-8"));
    socketChannel.write(dummyResponse);
    if (dummyResponse.remaining() > 0) {
        System.err.print("Filled UP");
    }
    System.out.println("Message Sent");
 //   key.interestOps(SelectionKey.OP_READ);
}

}

如您所见，我在端口9090上运行它localhost。为了测试繁重连接的代码，我开发了一个测试应用程序，该应用程序每秒运行一个新线程并连接到服务器。这是我的测试应用程序的代码：

    public class Main {
    /**
     * @param args
     */
    public static void main(String[] args) {
        int i = 0;
        try {
            while (i < 10000) {
                RunnableDemo temp = new RunnableDemo("Thread-"
                        + String.valueOf(i));
                temp.start();
                i++;
                Thread.sleep(1000);
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}
class RunnableDemo implements Runnable {
    private Thread t;
    private String threadName;
    InetAddress host = null;
    int port = 9090;
    RunnableDemo(String name) {
        threadName = name;
        System.err.println("Creating " + threadName);
    }
    public void run() {
        System.err.println("Running " + threadName);
        try {
            SocketChannel socketChannel = SocketChannel.open();
            socketChannel.connect(new InetSocketAddress(host, port));
            while (!socketChannel.finishConnect())
                ;
            System.out.println("Thread " + threadName + " Connected");
            ByteBuffer buffer = ByteBuffer.allocate(1024);
            while (true) {
                if (socketChannel.read(buffer) > 0) {
                    buffer.flip();
                    byte[] bytes = new byte[buffer.limit()];
                    buffer.get(bytes);  
                    System.out.println(threadName+ ":" + new String(bytes));
                    buffer.clear();
                }
            }
        } catch (Exception e) {
            System.out.println("Thread " + threadName + " interrupted.");
            e.printStackTrace();
        }
        System.out.println("Thread " + threadName + " exiting.");
    }
    public void start() {
        System.out.println("Starting " + threadName);
        try {
            host = InetAddress.getByName("127.0.0.1");
            if (t == null) {
                t = new Thread(this, threadName);
                t.start();
            }
        } catch (UnknownHostException e) {
            e.printStackTrace();
        }
    }
}

测试应用程序运行，但只有 75 个线程可以连接到服务器，第 75 个线程之后的所有线程都显示以下异常：

java.net.ConnectException: Connection refused: connect
at sun.nio.ch.Net.connect0(Native Method)
at sun.nio.ch.Net.connect(Unknown Source)
at sun.nio.ch.Net.connect(Unknown Source)
at sun.nio.ch.SocketChannelImpl.connect(Unknown Source)
at net.behboodi.client.RunnableDemo.run(Main.java:48)
at java.lang.Thread.run(Unknown Source)

套接字的并发连接数是否有任何限制？或者使用端口 127.0.0.1 和本地主机是否有任何限制？另一个想法是，也许Java应用程序或JVM不能创建超过75个线程。

我

搜索了所有这些，但没有找到任何答案来告诉我上述原因中我的主要问题是什么，以及如何修复代码以便我可以测试具有超过 10000 个并发线程的应用程序？

Answer 1

摆脱睡眠。选择器已阻止。沉睡在网络代码中只是浪费时间。注意 （1） 您不会在阻塞模式下调用finishConnect()，（2） 您没有将线程连接到 ServerChannel，而是将客户端套接字连接到服务器套接字，（3） 您的客户端代码不处理流结束，以及 （4） 这不是回显服务器。 – EJP