Re: Synchronization when collecting data from the EDT?

In article<TjZGp.40183$Vp.29218@newsfe14.iad>,
  Knute Johnson<nospam@knutejohnson.com> wrote:


[...]


The InvocationEvent is posted to the event queue and the calling thread
immediately enters wait(). It's up to the AWT event thread to dispatch
the enclosed Runnable.


Both invokeAndWait() (on the calling thread) and dispatch() (on the EDT)
synchronize on the (private) AWTInvocationLock.


This looks appealing; it reminds me of DF's suggestion of Exchanger.

[...]


Here's my (contrived) sscce. A javax.swing.Timer increments an int at
100 Hz, while a java.util.TimerTask samples the value at 1 Hz. I'd like
the API to be a little more explicit, but it does say that the calling
thread blocks and the Runnable's dispatch "will happen after all pending
events are processed."

import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.lang.reflect.InvocationTargetException;
import java.util.LinkedList;
import java.util.TimerTask;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.Timer;

/** @author John B. Matthews */
public class TwoTimer extends JPanel {

     private Timer timer = new Timer(10, null);
     private int value;

     public TwoTimer() {
         final JLabel label = new JLabel("0");
         timer.addActionListener(new ActionListener() {

             @Override
             public void actionPerformed(ActionEvent e) {
                 label.setText(String.valueOf(value++));
             }
         });
         this.add(label);
     }

     public int getValue() {
         return value;
     }

     public void startSwingTimer() {
         timer.start();
     }

     public void startUtilTimer() {
         final LinkedList<Integer> samples = new LinkedList<Integer>();
         java.util.Timer sampler = new java.util.Timer();
         sampler.scheduleAtFixedRate(new TimerTask() {

             @Override
             public void run() {
                 try {
                     EventQueue.invokeAndWait(new Runnable() {

                         @Override
                         public void run() {
                             samples.add(getValue());
                         }
                     });
                 } catch (InterruptedException ex) {
                     ex.printStackTrace(System.err);
                 } catch (InvocationTargetException ex) {
                     ex.printStackTrace(System.err);
                 }
                 System.out.println(samples.getLast());
             }
         }, 1000, 1000);

     }

     private void display() {
         JFrame f = new JFrame("TwoTimer");
         f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
         f.add(this);
         f.pack();
         f.setLocationRelativeTo(null);
         f.setVisible(true);
     }

     public static void main(String[] args) {
         EventQueue.invokeLater(new Runnable() {

             @Override
             public void run() {
                 TwoTimer tt = new TwoTimer();
                 tt.display();
                 tt.startSwingTimer();
                 tt.startUtilTimer();
             }
         });
     }
}