Mega Code Archive
Listing all threads and threadgroups in the VM
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/*
* Copyright (c) 2004 David Flanagan. All rights reserved.
* This code is from the book Java Examples in a Nutshell, 3nd Edition.
* It is provided AS-IS, WITHOUT ANY WARRANTY either expressed or implied.
* You may study, use, and modify it for any non-commercial purpose,
* including teaching and use in open-source projects.
* You may distribute it non-commercially as long as you retain this notice.
* For a commercial use license, or to purchase the book,
* please visit http://www.davidflanagan.com/javaexamples3.
*/
import java.awt.BorderLayout;
import java.io.PrintWriter;
import java.io.StringWriter;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
/**
* This class contains a useful static method for listing all threads and
* threadgroups in the VM. It also has a simple main() method so it can be run
* as a standalone program.
*/
public class ThreadLister {
/** Display information about a thread. */
private static void printThreadInfo(PrintWriter out, Thread t, String indent) {
if (t == null)
return;
out.println(indent + "Thread: " + t.getName() + " Priority: " + t.getPriority()
+ (t.isDaemon() ? " Daemon" : "") + (t.isAlive() ? "" : " Not Alive"));
}
/** Display info about a thread group and its threads and groups */
private static void printGroupInfo(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()
+ (g.isDaemon() ? " Daemon" : ""));
for (int i = 0; i < num_threads; i++)
printThreadInfo(out, threads[i], indent + " ");
for (int i = 0; i < num_groups; i++)
printGroupInfo(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
printGroupInfo(out, root_thread_group, "");
}
/**
* The main() method create a simple graphical user interface to display the
* threads in. This allows us to see the "event dispatch thread" used by AWT
* and Swing.
*/
public static void main(String[] args) {
// Create a simple Swing GUI
JFrame frame = new JFrame("ThreadLister Demo");
JTextArea textarea = new JTextArea();
frame.getContentPane().add(new JScrollPane(textarea), BorderLayout.CENTER);
frame.setSize(500, 400);
frame.setVisible(true);
// Get the threadlisting as a string using a StringWriter stream
StringWriter sout = new StringWriter(); // To capture the listing
PrintWriter out = new PrintWriter(sout);
ThreadLister.listAllThreads(out); // List threads to stream
out.close();
String threadListing = sout.toString(); // Get listing as a string
// Finally, display the thread listing in the GUI
textarea.setText(threadListing);
}
}
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