Multiple SwingWorkers

[Arne]

Im creating a swingworker thread after a button click of a gui to do some background work. From this new swingworker i have to start some new swingworker. this doesent work. the 2. thread never runs.

Here is some example code

class Thread1 extends Swingworker<Void,Void> {
  public Thread1() {
    execute();
  }

  public void doInBackground() {
    new Thread2();
  }

}

class Thread2 extends SwingWorker<Void,Void> {
  Thread2() {
    execute();
  }

  public void doInBackground() {
    .....do some work here
  }
}

After the button is clicked na Instance of Thread1 is created. The Thread1 starts and creates the object of Thread2, but thread 2 never starts running!!

Whats wrong with this code?

thx for any help

[Norm]

Could you post some code that compiles. Your code doesn't even with the ... commented out.

[Maxideon]

This was a bug (ID #6880336) that was introduced in java 6 update 18. In your example, the reason SwingWorker 2 doesn't start immediately is because your SwingWorker 1 hasn't finished yet. And in fact if your SwingWorker 1 waits on SwingWorker 2, then a deadlock occurs preventing all SwingWorkers from executing. This is the result of running all the workers on a single thread as stated in the bug report.

Technically the problem still exists before update 18, but you would have to create 10 simultaneous SwingWorkers before you notice anything.

[JosAH]

After the button is clicked na Instance of Thread1 is created. The Thread1 starts and creates the object of Thread2, but thread 2 never starts running!!

Whats wrong with this code?

Did you check that for a fact? Add a debug printline as the first line of your method:

  public void doInBackground() {
    System.out.println("running Thread2 ...");
    .....do some work here
  }

kind regards,

Jos

[Arne]

Yes i checked it with a debugger! The execute() command ist reached but doInBackround is never called

This was a bug (ID #6880336) that was introduced in java 6 update 18. In your example, the reason SwingWorker 2 doesn't start immediately is because your SwingWorker 1 hasn't finished yet

So if thread1 inherites from Thread instead from Swingworker this would work correctly?

[Maxideon]

Are you actually using the utilities of SwingWorker? That is, are you offloading the background task in doInBackground(), and updating a GUI in process() and/or done()? Changing it so that it extends thread instead will break that behavior.

[Norm]

With minor changes to your code to get it to compile, I get the following output showing that the code does execute:

Thread1 constr
Thread1 doInB
Thread2 constr
Thread2 doInB

[Arne]

Yes im only using the idDone() function to wait for the thread to get finished.
Could i use the getState() == Thread.State.Terminated function of the thread class instead?

With minor changes to your code to get it to compile, I get the following output showing that the code does execute:

Well i dont know why this example works and my programm doesnt. The example code is the exact same situation then in my programm.

[Arne]

k here is some working code that show the problem

package charts;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.*;

public class MyGui extends JFrame{

	public MyGui() {
		this.setSize(200, 100);
		JButton button = new JButton("TestMe");
		button.addActionListener(new ActionListener() {
			@Override
			public void actionPerformed(ActionEvent e) {
				new Thread1();
			}
		});
		this.add(button);
	}
	
	
	class Thread1 extends SwingWorker<Void,Void> {
		  public Thread1() {
			  System.out.println("Thread1 created");
			  execute();
		  }
	
		  public Void doInBackground() {
			  System.out.println("Thread1 running");
			  Thread2 thread2 = new Thread2();
			  while(true) {
				  if ( thread2.isDone()) {
					  break;
				  }
				  try {
					  Thread.sleep(1);
				  }
				  catch (InterruptedException e) {
					  e.printStackTrace();
				  }
			  }
			  return null;
		  }
	
		}

	class Thread2 extends SwingWorker<Void,Void> {
		Thread2() {
			System.out.println("Thread2 created");
			execute();
		}

		public Void doInBackground() {
			System.out.println("Thread2 running");
			return null;
		}
	}
	
	public static void main(String agrs[]) {
		MyGui gui = new MyGui();
		gui.setVisible(true);
	}
	
}

if thread1 cant finish, cause its waiting or doing some other task thread2 will never start.

Thats what Maxideon has written before.

In your example, the reason SwingWorker 2 doesn't start immediately is because your SwingWorker 1 hasn't finished yet

[Arne]

I changed the Swingworker class to Thread. Now everything works finde. Thx for the help!

[Brendan]

Hi Arne,

I am encountering the exact same problem. Can you please expand on what you mean? Possible put your solution into the example you gave earlier?

Thanks.

[PhQ]

Can't you just do

SwingWorker w1 = new SwignWorker(){
public void doInBackground() {
System.out.println("Thread 1running");
return null;
}
};

w.execute();

SwingWorker w2 = new SwignWorker(){
public void doInBackground() {
System.out.println("Thread 1running");
return null;
}
};
w2.execute();

[Brendan]

PhQ,

We are trying to prove concurrency, there is no concurrency in the example you just gave.