This section provides a tutorial example of simple deadlock demo program, SimpleDeadLock.java, with 2 threads waiting for each other.
In the previous section, "jstack" was used to print stack traces of all running threads of a given JVM process.
But "jstack" can also be used to detect deadlocks inside a given JVM process.
The tutorial example below shows you how "jstack" prints deadlock information:
1. Copy and save this Java program,
/**
* SimpleDeadLock.java
* Copyright (c) 2008 by Dr. Herong Yang, http://www.herongyang.com/
*/
import java.util.*;
public class SimpleDeadLock extends Thread {
public static Object l1 = new Object();
public static Object l2 = new Object();
private int index;
public static void main(String[] a) {
Thread t1 = new Thread1();
Thread t2 = new Thread2();
t1.start();
t2.start();
}
private static class Thread1 extends Thread {
public void run() {
synchronized (l1) {
System.out.println("Thread 1: Holding lock 1...");
try { Thread.sleep(10); }
catch (InterruptedException e) {}
System.out.println("Thread 1: Waiting for lock 2...");
synchronized (l2) {
System.out.println("Thread 2: Holding lock 1 & 2...");
}
}
}
}
private static class Thread2 extends Thread {
public void run() {
synchronized (l2) {
System.out.println("Thread 2: Holding lock 2...");
try { Thread.sleep(10); }
catch (InterruptedException e) {}
System.out.println("Thread 2: Waiting for lock 1...");
synchronized (l1) {
System.out.println("Thread 2: Holding lock 2 & 1...");
}
}
}
}
}
2. Compile and run SimpleDeadLock.java.
A deadlock will be created immediately between two running threads:
