This program can be integrated with your any java program to trace various states of a thread. It can help you to understand the flow of a thread. But remember, Tracer runs a thread to trace states of a thread. Tracer will not able to print all states of a thread. since there might be a situation when Tracer thread get served to CPU very late or with big interval and another thread changes its 3-4 states in between. I generally run Tracer 2-3 times for proper understanding.

I took its help to find out deadlock in my one of the program over nested monitor.

import java.lang.management.ManagementFactory;
import java.lang.management.ThreadMXBean;
import java.sql.Timestamp;
import java.util.ArrayList;
import java.util.Iterator;

/* 
 * (C) Copyright 2012-2013, by Amit Gupta (http://article-stack.com/).
 * 
 * This program is free software; you can redistribute it and/or modify it 
 * under the terms of the GNU Lesser General Public License as published by 
 * the Free Software Foundation; either version 2.1 of the License, or 
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but 
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 
 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, 
 * USA. OR see <http://www.gnu.org/licenses/>. 
 *
 * [Java is a trademark or registered trademark of Sun Microsystems, Inc. 
 * in the United States and other countries.]
 * 
 * ---------------------
 * Tracer.java
 * ---------------------
 * *
 */
public class Tracer {
	private ArrayList<WrapperThread> threadList;
	
	Tracer(){
		threadList = new ArrayList<WrapperThread>();
	}
	
	public void add(Thread t){
		threadList.add(new WrapperThread(t));
	}
	
	static{
		new Thread(new Runnable(){
			@Override
			public void run() {
				System.out.println("Monitoring Deadlocks");
				while(Thread.activeCount() >= 2)
					deadLockMonitor();
			}
		},"DeadLock Monitor").start();
	}
	
	private static void deadLockMonitor(){
		ThreadMXBean mx = ManagementFactory.getThreadMXBean();
		long[] DevilThreads = mx.findDeadlockedThreads();
		if(DevilThreads != null && DevilThreads.length > 0){
			System.out.println(currentTime() + "Deadlock detected");
			for(int i=0;i<DevilThreads.length; i++){
				System.out.println("Thread id :" + DevilThreads[i]);
			}
			System.out.println("Exiting from system");
			System.exit(0);
		}
	}
	
	public void trace() {
		new Thread(new Runnable(){
			@Override
			public void run() {
				Iterator<WrapperThread> itr;
				while(Thread.activeCount() >= 2){
					itr = threadList.iterator();
					while(itr.hasNext()){
						WrapperThread wt = itr.next();
						if(wt.isStateChanged()){
							System.out.print(currentTime() + " :: " + wt.originalThread.getName()+":"+wt.currentState + "\n");
						}
					}
				}
			}
		},"Tracer").start();
	}
	
	public static void traceImmediate(final Thread t) {
		new Thread(new Runnable(){
			@Override
			public void run() {
				WrapperThread wt = new WrapperThread(t);
				while(Thread.activeCount() >= 2){
						if(wt.isStateChanged()){
							System.out.print(currentTime() + " :: " + wt.originalThread.getName()+":"+wt.currentState + "\n");
						}
					}
			}
		},"Immediate Tracer").start();		
	}
	
	public static String currentTime(){
		return (new Timestamp(System.currentTimeMillis())).toString();
	}
}

How to use it in your program

		Tracer t = new Tracer();
		t.add(A);
		t.add(B);
		t.trace();

Or

		Tracer.traceImmediate(A);
		Tracer.traceImmediate(B);

Happy coding

Amit Gupta

Hey! this is Amit Gupta (amty). By profession, I am a Software Eng. And teaching is my passion. Sometimes I am a teacher, as you can see many technical tutorials on my site, sometimes I am a poet, And sometime just a friend of friends...