java应用程序tcp连接丢失检测在Windows 7中有所不同？

Question

I have a java application running on Windows XP and also on Windows 7. This application has an open tcp connection to another computer.

Now comes the point: On an XP machine unpugging the network cable has a nearly immidiate effect on my inputstream.read method by returning -1 or SocketException. That's one thing how I detect network connection loss. On the Win7 machine when the network cable is unplugged windows itself tells me this in its connection icon in the task bar but my java application doesn't get any hint of this. It stays as if nothing happened.

Does TCP behaves differently on windows 7 or does windows7 shield this information from its applications?

package tcpconnectionlossdetectiontest;

import java.io.IOException;
import java.io.InputStream;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.SocketException;
import java.net.SocketTimeoutException;

public class TcpListener extends Thread {
  private int _portNo = 23456;
  private boolean _done = false;

  public static void main(String[] args) {
    int port = 23456;

    if (args.length > 0) {
      int position = -1;
      do {
        String arg = args[++position].trim();
        if (arg.equalsIgnoreCase("-p") || arg.equalsIgnoreCase("--PortNo")) {
          String argParameter = args[++position].trim();
          // e.g. store additional argument
          try {
            port = Integer.parseInt(argParameter);
          } catch (NumberFormatException nfex) {
            port = 23456;
          }
          System.out.println("Argument " + position + " (" + arg + ", " + argParameter + "): port number set to " + port);
        } else {
          System.out.println("Argument " + position + " (" + arg + ") unknown.");
        }
      }
      while (position + 1 < args.length);
      // Parsing command line arguments ready.
    }

    TcpListener listener = new TcpListener(port);
    listener.start();
  }

  public TcpListener(int portNo) {
    this._portNo = portNo;
  }

  public void run() {
    Socket s = null;
    InputStream is = null;
    byte[] buf = new byte[1000];
    int readResult = 0;
    int maxOpen = 3;
    int openCounter = 0;
    try {
      ServerSocket sSocket = new ServerSocket(this._portNo);
      while (openCounter < maxOpen) {
        if (s == null) {
          try {
            System.out.println("waiting for connection on port " + this._portNo);
            sSocket.setSoTimeout(60000);
            s = sSocket.accept();
            if (s != null) {
              System.out.println("got connection on port " + this._portNo);
              openCounter++;
              is = s.getInputStream();
            }
          } catch (SocketTimeoutException stex) {
            System.out.println("no connection yet...");
          }
        }
        if (s != null && is != null) {
          readResult = is.read(buf, 0, 1000);
        }
        if (readResult == -1) {
          readResult = 0;
          System.out.println("connection broken...");
          is=null;
          if (s != null) {
            s.close();
            s=null;
          }
        } else if (readResult > 0) {
          System.out.println("Data read: " + new String (buf,0,readResult));
        }
      }
    } catch (IOException ioex) {
      System.out.println("IO exception caught:");
      ioex.printStackTrace();
    }
    this._done = true;
  }
}

Result on windows xp after round about 5 seconds is after disconnection is:

waiting for connection on port 23456
no connection yet...
waiting for connection on port 23456
got connection on port 23456
Data read: Here is a connection from win7 to xp...
Data read: 

IO exception caught:
java.net.SocketException: Connection reset
    at java.net.SocketInputStream.read(SocketInputStream.java:168)
    at tcpconnectionlossdetectiontest.TcpListener.run(TcpListener.java:73)
Process exited with exit code 0.

Result on windows 7 after disconnection is: ... nothing. Application stays open without disconnect detection.

@edit 2013-02-01 09:54: Happens in jre6 and jre7.

@edit 2013-02-01 10:59: Happens in 32bit and 64bit java. Happens on Win7 Laptop and normal PC.

@edit 2013-02-01 12:40: Code example and result added.

@edit 2031-02-06: Since I found nothing on the internet and nobody had a solution for this, I added an active ping-pong mechanism to our applications. Now I can detect after at most 20 sec. that the connection is broken.

@edit 2013-02-08: Another way to find out about the status is 'netsh interface ip show interfaces' but that command line result must be parsed in java before knowing the status. Maybe there is a better way to get that information.

Answer 1

TCP/IP on Win7 is different than the implementation on XP. One important issue is that it includes something they call Auto-Tuning. It's designed to optimize throughput and such, but there could be unintended side-effects for passing connection status changes to the JVM.

Check out the thread here for more information including how to turn it off: http://social.technet.microsoft.com/Forums/en-US/w7itpronetworking/thread/1a6197df-ada7-4b12-92b7-a8a2f454f9a3