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 0x00000000d6f649b8represent the two resource String “ABAP” and
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.