Stopping a Thread that creates Threads for Socket I/O 1

[TheInsider]

Hi,

I'm having trouble with the simple daemon that I'm writing. It's a pretty basic socket I/O application: a Daemon thread loops, waiting for client connections. When a client connection request is made, the Daemon creates a new Connection thread to handle it and goes back to listen for more connections. This part works fine, but the problem occurs when I try to stop the Daemon thread and restart it.

Here's the scenario: If I start the daemon to listen to port 12345 and then stop the daemon and then start the daemon again on port 12345, I get "java.net.BindException: Address already in use: JVM_Bind" because the Connection thread(s) from the first time I ran the daemon still haven't been disconnected.

Here is the portion of the code that is causing the problem:

public class ConfigWindow extends JDialog implements ActionListener {
	private Daemon daemon;
	private Thread thread = null;
...
	public void actionPerformed(ActionEvent ae) {
		if ("start".equals(ae.getActionCommand())) {
			daemon = new Daemon(12345);
			thread = new Thread(daemon);
			thread.setDaemon(true);
			thread.start();
		} else if ("stop".equals(ae.getActionCommand())) {
			daemon.stop();
			thread = null;
		}
	} // actionPerformed
...
} // ConfigWindow

package server;
import java.io.*;
import java.net.*;

public class Daemon implements Runnable {
	private int port = 0;
	private boolean isAlive;

	public Daemon() {
	} // default constructor

	public Daemon(int port) {
		this.port = port;
	} // optional constructor

	public void run() {
		try {
			ServerSocket socket = new ServerSocket(port);
			isAlive = true;
			while (isAlive) {
				Thread thread = new Thread(new Connection(socket.accept()));
				thread.setDaemon(true);
				thread.start();
			}
			socket.close();
		} catch (IOException ioe) {
			System.err.println(ioe);
			System.exit(-1);
		}
	} // run

	public void setPort(int port) {
		this.port = port;
	} // setPort

	public void stop() {
		isAlive = false;
	} // stop
} // Daemon

package server;
import java.io.*;
import java.net.*;

public class Connection implements Runnable {
	private Socket socket;

	public Connection(Socket socket) {
		this.socket = socket;
	} // constructor

	public void run() {
		try {
// will do something here eventually
			socket.close();
		} catch (IOException ioe) {
		}
	} // run
} // Connection

If, in the while loop of Daemon's run(), I don't connect to anything, the daemon will shut down and restart on the same port # without any problems. However, when I run the code as it is above, the port # is held open, and if ConfigWindow.actionPerformed() is called again from clicking the start button (not shown above), the program will end with a "java.net.BindException: Address already in use: JVM_Bind".

I don't think this should be that complicated. Someone with thread and socket I/O experience should be able to spot the problem right away.

Thanks

 

[TheInsider]

Just to follow up; I got an answer on another forum, so I'll post it here in case anyone else ever encounters this problem. If I get rid of the isAlive variable and simply have while(true), I can place socket.close() in Daemon.stop(). When stop() is called, the while loop will terminate on a SocketClosed() exception, which I can just ignore.

 

[stefanwagner]

Returning and explaining the solution deserves a star.

don't visit my homepage:

http://home.arcor.de/hirnstrom/bewerbung

 

[Diancecht]

Glad you got it working, and I really appreciate like stefan that you came back to post the sollution, but I don't like that sollution.

Maybe setting the isAlive variable as volatile could help things to work:

Stopping threads

Cheers,
Dian

 

[TheInsider]

Thanks, I will have a look at the tutorial you referenced.