An example of Deadlock detection using JDK standard tool: jstack

[JerryWang]

We can get the concept of deadlock in wikipedia.

The picture below gives a common scenario which leads to deadlock.

In this blog, I will share how to detect deadlock situation using JDK standard tool jstack.

First we have to write a Java program which will lead to Deadlock:

package thread;



public class DeadLockExample {

/*



  * Thread 1: locked resource 1



    Thread 2: locked resource 2



  */



public static void main(String[] args) {



  final String resource1 = "ABAP";



  final String resource2 = "Java";



  // t1 tries to lock resource1 then resource2



  Thread t1 = new Thread() {



   public void run() {



    synchronized (resource1) {



     System.out.println("Thread 1: locked resource 1");



     try {



      Thread.sleep(100);



     } catch (Exception e) {



     }



     synchronized (resource2) {



      System.out.println("Thread 1: locked resource 2");



     }



    }



   }



  };



  Thread t2 = new Thread() {



   public void run() {



    synchronized (resource2) {



     System.out.println("Thread 2: locked resource 2");



     try {



      Thread.sleep(100);



     } catch (Exception e) {



     }



     synchronized (resource1) {



      System.out.println("Thread 2: locked resource 1");



     }



    }



   }



  };



  t1.start();



  t2.start();



}



}

Execute this program, you will get output:

Thread 1: locked resource 1

Thread 2: locked resource 2

Then use command jps -l -m to list the process id of this deadlock program. In my example it is 51476:

Just type jstack + process id, and it will display all detailed information about deadlock:

Here the object 0x00000000d6f64988 and 0x00000000d6f649b8 represent the two resource String "ABAP" and "Java".

Update on 2017-03-04 Saturday 10:35PM - how to get the thread state of a long-running application

Suppose you have found a long-running application which has high CPU utilization rate and you would like to know which exactly line is relevant.

Use the following code to simulate the long running situation:

package thread;



import java.util.ArrayList;

import java.util.List;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;





class MyThread implements Runnable{



	private List<Integer> myList;

	private Object host;

	public MyThread(List<Integer> list, Object object){

		this.myList = list;

		this.host = object;

	}

	

	public void updateListSafe(){

		synchronized(this.host){

			ArrayList<Integer> safe = new ArrayList<Integer>();

			safe.add(1);

		}

	}

	

	private void updateList(int i){

		synchronized(this.host){

			myList.add(i);

		}

	}



	@Override

	public void run() {

		while(true){

			updateList(1);

		}

	}

	

}

public class MyExecutor {



	private ArrayList<Integer> taskList = new ArrayList<Integer>();

	private Object object = new Object();

	private void launch(){

		

        ExecutorService executorService= Executors.newFixedThreadPool(10);



        executorService.execute(new MyThread(taskList, object));

        executorService.execute(new MyThread(taskList, object));

	}

	public static void main(String[] args) {

		MyExecutor test = new MyExecutor();

		test.launch();

	}

}

first find the process id of running application:



then use command jstack 23520 to get the stack trace:

In line 9 and line 18 our application method MyThread.updateList is listed there.