AWT Bug? Threading problem? Or am I losing my mind?

[Dustin Lang]

Hi,

I'm building a versioning server-client pair using RMI and I thought it
would be fun to have a little traffic light to indicate that something is
happening: green means go ahead, red means it's busy doing something.  I
wrote Light.java, an excruciatingly simple traffic light.  At the start of
the actionPerformed method in the versioning client, I set it red (which
calls repaint internally), and at the end I set it green.  There's only 
one problem: it doesn't work.

I wrote a little demo (Test.java)

Here's what happens:
when setColor is called in some places (say, the Test constructor), it
works just fine (whee, it's a traffic light!).  when setColor is called
within the actionPerformed method, the repaint doesn't go through until
the end of the actionPerformed method is reached.  I tried doing
repaint(10L), with the same result.

Here's my explanation:
the event distributing thread is a higher-priority thread than the 
repainting one, and this somehow messes up the repaint() call.

Let's make the assumption that I haven't made a glaring error (may not be
a reasonable assumption since my brain is a bit fried), and assume that
this is in fact a bug.  Now, this is by no means a major bug, and I'm sure
I could do a work-around, but if repaint(10L) is called, shouldn't paint
get called within 10 ms, regardless of what other threads are executing?
Or am I on crack?

Thanks,
dstn.


import java.awt.*;
import java.awt.event.*;

public class Test extends Frame implements ActionListener {

        Light light;
        Button go;

        public static void main(String[] args) {
                new Test();
        }

        public Test() {
                light = new Light(15);
                light.setColor(Color.green);
                go = new Button("Go!");
                go.addActionListener(this);
                setBackground(Color.white);
                add("North", go);
                add("South", light);
                setTitle("Test!");
                pack();
                show();
        }

        public void actionPerformed(ActionEvent e) {
                light.setColor(Color.red);
                try {
                        Thread.sleep(2000L);
                } catch (InterruptedException ie) {
                }
                light.setColor(Color.blue);
                try {
                        Thread.sleep(2000L);
                } catch (InterruptedException ie) {
                }
                light.setColor(Color.green);
        }
}

import java.awt.*;

public class Light extends Canvas {

        int dia;

        public Light(int d) {
                dia = d;
        }

        public Dimension getPreferredSize() {
                return new Dimension(dia,dia);
        }

        public void setColor(Color c) {
                setForeground(c);
                System.out.println("Repaint!");
                repaint(10L);
        }

        public void update(Graphics g) {
                System.out.println("Update!");
                paint(g);
        }

        public void paint(Graphics g) {
                System.out.println("Painting (color is " + getForeground().toString() 
+ ")");
                g.setColor(getBackground());
                g.fillRect(0,0,getSize().width,getSize().height);
                g.setColor(getForeground());
                g.fillOval(0,0,dia,dia);
        }
}