Listing and Interrupting AWT Threads

Java Swing Tutorials - Herong's Tutorial Examples

∟Listing and Interrupting AWT Threads

This section provides a tutorial example on how to list AWT threads and how to interrupt AWT threads with the interrupt() method.

Problem: I want to know how many threads are created by the Swing package and the AWT package. And what will happen if I send the interrupt signal to all of them.

Solution: This is easy. Just get the list of all threads of the current thread group, and interrupt them one by one. Here is a sample program to show you how to do this:

/* FrameThreads.java
 * Copyright (c) 1997-2018 HerongYang.com. All Rights Reserved.
 */
import java.awt.*;
import javax.swing.*;
public class FrameThreads {
   public static void main(String[] a) {
      JFrame f = new JFrame("Frame 1");
      f.setBounds(0,0,100,100);
      f.setVisible(true);
      f = new JFrame("Frame 2");
      f.setBounds(50,50,100,100);
      f.setVisible(true);
      f = new JFrame("Frame 3");
      f.setBounds(100,100,100,100);
      f.setVisible(true);
      Thread[] l = new Thread[100];
      int n = Thread.enumerate(l);
      Thread g = null;
      for (int i=0; i<n; i++) {
         System.out.println("Active thread = "+l[i].getName());
      }
      Thread t = Thread.currentThread();
      for (int i=0; i<n; i++) {
         try {
            Thread.sleep(1000*30);
         } catch (Exception e) {
            System.out.println("Interrupted.");
         }
         if (t != l[i]) {
            System.out.println("Interrupting thread = "
               +l[i].getName());
            l[i].interrupt();
         }
      }
   }
}

If you run this program with JDK 1.5 or older, you will see 3 frame windows showing up on the screen. After every 30 seconds, my program will send an interrupt signal to each thread. When the interrupt signal reaches the "Java2D Disposer" thread, a run-time exception occurs forcing the application to terminate. The following list shows you the output of my program:

herong> \Progra~1\Java\jdk1.5.0_09\bin\java FrameThreads

Active thread = main
Active thread = AWT-Windows
Active thread = AWT-Shutdown
Active thread = AWT-EventQueue-0
Active thread = Java2D Disposer
Interrupting thread = AWT-Windows
Interrupting thread = AWT-Shutdown
Interrupting thread = AWT-EventQueue-0
Interrupting thread = Java2D Disposer
Exception while removing reference: java.lang.InterruptedException
java.lang.InterruptedException
   at java.lang.Object.wait(Native Method)
   at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:111)
   at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:127)
   at sun.java2d.Disposer.run(Disposer.java:100)
   at java.lang.Thread.run(Thread.java:534)
AWT blocker activation interrupted:
java.lang.InterruptedException
   at java.lang.Object.wait(Native Method)
   at java.lang.Object.wait(Object.java:429)
   at sun.awt.AWTAutoShutdown.activateBlockerThread(AWTAutoShut...
   at sun.awt.AWTAutoShutdown.setToolkitBusy(AWTAutoShutdown.ja...
   at sun.awt.AWTAutoShutdown.notifyToolkitThreadBusy(AWTAutoSh...
   at sun.awt.windows.WToolkit.eventLoop(Native Method)
   at sun.awt.windows.WToolkit.run(WToolkit.java:262)
   at java.lang.Thread.run(Thread.java:534)