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ImageJ is an open source Java image processing program inspired by NIH Image for the Macintosh.

There is a newer version: 1.54m

package ij.plugin;
import java.io.*;
import ij.*;
import ij.text.*;
import javax.swing.SwingUtilities;

/**
* Displays thread information in a text window.
*
* This code is from the book _Java in a Nutshell_ by David Flanagan.
* Written by David Flanagan.
*/
public class ThreadLister implements PlugIn {

	public void run(String arg) {
		if (IJ.getApplet()!=null)
			return;
		CharArrayWriter caw = new CharArrayWriter();
		PrintWriter pw = new PrintWriter(caw);
		try {
			listAllThreads(pw);
			new TextWindow("Threads", caw.toString(), 420, 420);
		} catch
			(Exception e) {}
			
		// cause an exception on the EDT
		if (IJ.altKeyDown()) {
			SwingUtilities.invokeLater(new Runnable() {
			  public void run() {
				((Object) null).toString();        
			  }
			});
		}
		// cause an exception off the EDT
		//((Object) null).toString();

	}


    // Display info about a thread.
    private static void print_thread_info(PrintWriter out, Thread t, 
                          String indent) {
        if (t == null) return;
        out.print(indent + "Thread: " + t.getName() +
                "  Priority: " + t.getPriority() +
                (t.isDaemon()?" Daemon":"") +
                (t.isAlive()?"":" Not Alive") + "\n");
    }
    
    // Display info about a thread group and its threads and groups
    private static void list_group(PrintWriter out, ThreadGroup g, 
                       String indent) {
        if (g == null) return;
        int num_threads = g.activeCount();
        int num_groups = g.activeGroupCount();
        Thread[] threads = new Thread[num_threads];
        ThreadGroup[] groups = new ThreadGroup[num_groups];
        
        g.enumerate(threads, false);
        g.enumerate(groups, false);
        
        out.println(indent + "Thread Group: " + g.getName() + 
            "  Max Priority: " + g.getMaxPriority() + "\n");
        
        for(int i = 0; i < num_threads; i++)
            print_thread_info(out, threads[i], indent + "    ");
        for(int i = 0; i < num_groups; i++)
            list_group(out, groups[i], indent + "    ");
    }
    
    // Find the root thread group and list it recursively
    public static void listAllThreads(PrintWriter out) {
        ThreadGroup current_thread_group;
        ThreadGroup root_thread_group;
        ThreadGroup parent;
        
        // Get the current thread group
        current_thread_group = Thread.currentThread().getThreadGroup();
        
        // Now go find the root thread group
        root_thread_group = current_thread_group;
        parent = root_thread_group.getParent();
        while(parent != null) {
            root_thread_group = parent;
            parent = parent.getParent();
        }
        
        // And list it, recursively
        list_group(out, root_thread_group, "");
    }
    
}