We can get the concept of deadlock in wikipedia.
The picture below gives a common scenario which leads to deadlock.
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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:
monospace; font-size: inherit; background-color: inherit;">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:
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Just type jstack + process id, and it will display all detailed information about deadlock:
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Here the object 0x00000000d6f64988 and 0x00000000d6f649b8represent the two resource String “ABAP” and “Java”.
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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:
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then use command jstack 23520 to get the stack trace:
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In line 9 and line 18 our application method MyThread.updateList is listed there.
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