Name: gm110360 Date: 05/05/2004


FULL PRODUCT VERSION :
java version "1.4.2_04"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.2_04-b05)
Java HotSpot(TM) Client VM (build 1.4.2_04-b05, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows 2000 [Version 5.00.2195]

A DESCRIPTION OF THE PROBLEM :
It appears that appending text to a JTextArea _while_ the frame containing that text area is being displayed (JFrame#show()) a deadlock can occur. Interestingly, this seems to only happen if the JTextArea#append() is called on the Event Dispatch Thead (the method is documented as being thread-safe, but habit has me doing these things on the Event Dispatch Thread anyway).

I have a test program that will always reproduce the problem. It first creates a JTextArea, then a thread that continuously appends to that text area. Then a simple frame containing the text area is created and shown. If the show() does not deadlock, the frame is disposed and a new one created and shown. After a few iterations (never more than 50 for me) the show() will deadlock. If the updater thread is changed to call the Runner#run() method directly instead of using SwingUtilities#invokeAndWait(), the deadlock does not seem to occur (after over 500 iterations on my machine).

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Compile and run the attached class.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
I would expect the program to run without deadlocking.
ACTUAL -
The program deadlocks.

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import javax.swing.*;

public class DocumentDeadlockTest
{
   public static void main(String[] args)
   {
      final JTextArea textArea = new JTextArea();

      Thread busyThread = new Thread()
      {
         public void run()
         {
            Runnable runner = new Runnable()
            {
               public void run()
               {
                  textArea.append("1234567890123456789012345678901234567890");
               }
            };

            while (true)
            {
               try
               {
                  SwingUtilities.invokeAndWait(runner);
                  //runner.run();
               }
               catch (Exception e)
               {
                  e.printStackTrace();
               }
            }
         }
      };
      busyThread.start();

      int i = 0;
      while (true)
      {
         JFrame frame = createFrame(textArea);
         frame.show();
         System.out.println("Iteration " + (++i) + " with no deadlock");
         frame.dispose();
      }
   }

   private static JFrame createFrame(JTextArea textArea)
   {
      JFrame frame = new JFrame("Document Deadlock Test");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().setLayout(new BoxLayout(frame.getContentPane(), BoxLayout.X_AXIS));
      frame.getContentPane().add(textArea);
      frame.setSize(200, 200);
      frame.setLocationRelativeTo(null);
      return frame;
   }
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Don't append() to the JTextArea from the Event Dispatch Thread. This is a simple workaround, but realizing that this bug is the reason for the deadlock can be quite challenging.
(Incident Review ID: 261127)
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