Java Thread Deadlock Demo Program

Java Tools Tutorials - Herong's Tutorial Examples

∟Java Thread Deadlock Demo Program

This section provides a tutorial example of simple deadlock demo program, SimpleDeadLock.java, with 2 threads waiting for each other.

In a tutorial presented earlier, "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) 2005 HerongYang.com. All Rights Reserved.
 */
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:

herong> javac SimpleDeadLock.java

herong> java SimpleDeadLock

Thread 1: Holding lock 1...
Thread 2: Holding lock 2...
Thread 2: Waiting for lock 1...
Thread 1: Waiting for lock 2...