Flags and the Event Thread

Question

I was writing code for a game and I realized that the AWT event thread could change the value of a flag while I'm in the process of updating the game state. This can cause a few problems, or it could even leave events not handled because of it. I see code like this all the time as a fix to the threading issues, am I missing something or is it really a solution? I can't post the actual code as it's too long, so I created a simple example:
import java.awt.event.*;
import javax.swing.*;
public class EventTest extends JFrame implements KeyListener, Runnable
     private boolean isKeyDown;
     public EventTest()
          setSize(500, 500);
          setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
          setVisible(true);
          addKeyListener(this);
          new Thread(this).start();
     public void keyPressed(KeyEvent event)
          //synchronized(this)
               isKeyDown = true;
     public void keyReleased(KeyEvent event)
          //synchronized(this)
               isKeyDown = false;
     public void keyTyped(KeyEvent event) {}
     public void run()
          // game loop
          while(true)
               //synchronized(this)
                    boolean cache = isKeyDown;
                    System.out.print(isKeyDown); // before
                    System.out.print(' ');
                    /* event handling, game logic, etc. done here
                       do some useless operation to simulate this */
                    long time = System.currentTimeMillis();
                    while(time + 1 > System.currentTimeMillis());
                    System.out.println(isKeyDown); // after
                    if(cache != isKeyDown)
                         System.out.println("PROBLEM!");
                    // render everything to the screen
               try
                    Thread.sleep(100);
               } catch(InterruptedException e) {}
     public static void main(String[] args)
          new EventTest();
}Basically I have a game loop, where I update the game state, handle events, then draw things to the screen. Each time a key is pressed or released, I set the appropriate value to isKeyDown from the AWT event thread. The desirable output is to have the booleans equal to each other so that "false false" or "true true" is printed out on the screen constantly, but once in a while I'll get a "false true" or "true false", which is expected but obviously not wanted.
So one solution is right there commented out (synchronizing), though most people seem to avoid it. I see everybody using flags like this, so I'm wondering if I'm missing some obvious solution to the problem or if it's really even that big of a deal. I don't see any other fix, but that's why you're all here. ;)
Thanks.

Answer 1

Swing related questions should be posted in the Swing forum.
I converted your simple example to use a Swing Timer instead of a while(true) loop with a Thread.sleep. I experienced no problems as expected since all the code will be executed in the Event Dispatch Thread (EDT).
Of course using this approach could make the game less responsive if your game logic is extensive and hogs the EDT, but given that you try to invoke your game logic every 100 millisecond I assume it can't be that extensive.
Anyway here is the code I used as a test:
import java.awt.event.*;
import javax.swing.*;
public class EventTest extends JFrame implements KeyListener, ActionListener
     private boolean isKeyDown;
     public EventTest()
          setSize(500, 500);
          setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
          setVisible(true);
          addKeyListener(this);
          new Timer(100, this).start();
     public void keyPressed(KeyEvent event)
          isKeyDown = true;
     public void keyReleased(KeyEvent event)
          isKeyDown = false;
     public void keyTyped(KeyEvent event) {}
     public void actionPerformed(ActionEvent e)
          boolean cache = isKeyDown;
          System.out.print(isKeyDown); // before
          System.out.print(' ');
          /* event handling, game logic, etc. done here
             do some useless operation to simulate this */
          long time = System.currentTimeMillis();
          while(time + 1 > System.currentTimeMillis());
          System.out.println(isKeyDown); // after
          if(cache != isKeyDown)
               System.out.println("PROBLEM!");
     public static void main(String[] args)
          new EventTest();
}