Stopping a thread using a stop button - GUI

[Ben1]

Hi all,
I've got an app all made, looking lovely.

But... I have a GUI that has start and stop buttons. Start button kicks off a new thread to capture packets. Working fine.

The stop button, this needs to stop capturing the packets but keep the actual program running - so System.exit(); isn't suitable (different button for that).

I've read up on it and it seems like interrupt is my best bet but I can't get it to work. Is there just a simple line that I can put in to stop the thread?

Thanks
Ben

[KevinWorkman]

You could check a boolean in your Thread and return when it's false. Then just update that variable when the stop button is pressed.

[Ben1]

I like it.

That works and it stops capturing packets. But then if I click the start button again I get a load of errors...

**
Exception occurred during event dispatching:
java.lang.IllegalThreadStateException
at java.lang.Thread.start(Thread.java:638)
at GUI.IMsafeGUI.StartActionPerformed(IMsafeGUI.java: 497)
at GUI.IMsafeGUI.access$1000(IMsafeGUI.java:34)
at GUI.IMsafeGUI$12.actionPerformed(IMsafeGUI.java:44 5)
at javax.swing.AbstractButton.fireActionPerformed(Abs tractButton.java:1995)
at javax.swing.AbstractButton$Handler.actionPerformed (AbstractButton.java:2318)
at javax.swing.DefaultButtonModel.fireActionPerformed (DefaultButtonModel.java:387)
at javax.swing.DefaultButtonModel.setPressed(DefaultB uttonModel.java:242)
at javax.swing.plaf.basic.BasicButtonListener.mouseRe leased(BasicButtonListener.java:236)
at java.awt.Component.processMouseEvent(Component.jav a:6267)
at javax.swing.JComponent.processMouseEvent(JComponen t.java:3267)
at java.awt.Component.processEvent(Component.java:603 2)
at java.awt.Container.processEvent(Container.java:204 1)
at java.awt.Component.dispatchEventImpl(Component.jav a:4630)
at java.awt.Container.dispatchEventImpl(Container.jav a:2099)
at java.awt.Component.dispatchEvent(Component.java:44 60)
at java.awt.LightweightDispatcher.retargetMouseEvent( Container.java:4577)
at java.awt.LightweightDispatcher.processMouseEvent(C ontainer.java:4238)
at java.awt.LightweightDispatcher.dispatchEvent(Conta iner.java:4168)
at java.awt.Container.dispatchEventImpl(Container.jav a:2085)
at java.awt.Window.dispatchEventImpl(Window.java:2478 )
at java.awt.Component.dispatchEvent(Component.java:44 60)
at java.awt.EventQueue.dispatchEvent(EventQueue.java: 599)
at java.awt.EventDispatchThread.pumpOneEventForFilter s(EventDispatchThread.java:269)
at java.awt.EventDispatchThread.pumpEventsForFilter(E ventDispatchThread.java:184)
at java.awt.EventDispatchThread.pumpEventsForFilter(E ventDispatchThread.java:178)
at java.awt.Dialog$1.run(Dialog.java:1046)
at java.awt.Dialog$3.run(Dialog.java:1098)
at java.security.AccessController.doPrivileged(Native Method)
at java.awt.Dialog.show(Dialog.java:1096)
at java.awt.Component.show(Component.java:1563)
at java.awt.Component.setVisible(Component.java:1515)
at java.awt.Window.setVisible(Window.java:842)
at java.awt.Dialog.setVisible(Dialog.java:986)
at GUI.IMsafeGUI$14.run(IMsafeGUI.java:643)
at java.awt.event.InvocationEvent.dispatch(Invocation Event.java:209)
at java.awt.EventQueue.dispatchEvent(EventQueue.java: 597)
at java.awt.EventDispatchThread.pumpOneEventForFilter s(EventDispatchThread.java:269)
at java.awt.EventDispatchThread.pumpEventsForFilter(E ventDispatchThread.java:184)
at java.awt.EventDispatchThread.pumpEventsForHierarch y(EventDispatchThread.java:174)
at java.awt.EventDispatchThread.pumpEvents(EventDispa tchThread.java:169)
at java.awt.EventDispatchThread.pumpEvents(EventDispa tchThread.java:161)
at java.awt.EventDispatchThread.run(EventDispatchThre ad.java:122)

**



Any ideas?


Thanks
Ben

[KevinWorkman]

I can't really comment on your code as you haven't posted any :p

If you want to post code, make sure it's as small as possible- preferably in SSCCE form.

But I would guess that you're trying to start a Thread that has already been started and completed. Chances are you want to start a new Thread each time you press Start (making sure the old one has stopped first), possibly using the same instance of Runnable.

[Ben1]

Yeah, it's throwing the error because I'm trying to start a thread that's already running. And I know I need to stop the first one before I can start the new one... that was my original question :P

The code below is the part that contains your suggested boolean (toRun) and is the run thread that everything else spawns from. Stopping this class from running will stop everything that follows it.

public class IMsafe {

    public static boolean toRun = true;

    public static void run(int selectedIndex) throws IOException {

        NetworkInterface[] devices = JpcapCaptor.getDeviceList();
        JpcapCaptor captor = JpcapCaptor.openDevice(devices[selectedIndex], -1, false, 20);
        ActiveThreads activeThreads = new ActiveThreads();
        int count = 0;
        Packet tempPacket = captor.getPacket();
        for (selectedIndex = 0; selectedIndex < 10; selectedIndex++) {
            if (toRun == true) {
                if (tempPacket != null) {

                    //count++;
                    //System.out.println("still monitoring: " + count);
                    new Thread(new CapturePackets(captor, tempPacket, activeThreads)).start();
                    tempPacket = captor.getPacket();
                    selectedIndex = 0;
                } else {
                    tempPacket = captor.getPacket();
                    selectedIndex = 0;
                }
            } else{
                return;
            }
        }
    }
}

I THINK the problem above is that by the time the class started capturing packets the thread has already started etc. But I can't put the boolean check above the for loop because obviously once it's in the loop it won't stop until the NIC stops capturing packets... never gonna happen.

Any suggestions?

Ben

[KevinWorkman]

I honestly don't really understand what's going on in that code, as it contains a bunch of external classes- which is where that SSCCE would come in handy.

But for what it's worth, here is the short example I came up with:

public class ThreadTest {
 
	public static void main(String[] args) throws Exception {
	
		Runnable r = new Runnable(){
			public void run(){
				System.out.println("Running.");
			}
		};
		
		new Thread(r).start();
		Thread.sleep(1000);
		new Thread(r).start();
	}
}

Your check against the boolean would go inside the run() method. Also, for what it's worth, the method of using a boolean to stop the Thread is actually described in the documentation for the deprecated Thread.stop() method.

Thread (Java Platform SE 6)