How to Create a Deadlock Scenario Programatically

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Deadlock is a special scenario in the multi-threaded environment where two or more threads are blocked forever. The deadlock situation arises with at least two threads and two or more threads.

public class ThreadDeadlock {

public static void main(String[] args) throws InterruptedException { Object obj1 = new Object(); Object obj2 = new Object(); Object obj3 = new Object(); Thread t1 = new Thread(new SyncThread(obj1, obj2), "t1"); Thread t2 = new Thread(new SyncThread(obj2, obj3), "t2"); Thread t3 = new Thread(new SyncThread(obj3, obj1), "t3"); t1.start(); Thread.sleep(5000); t2.start(); Thread.sleep(5000); t3.start(); } } class SyncThread implements Runnable{ private Object obj1; private Object obj2; public SyncThread(Object o1, Object o2){ this.obj1=o1; this.obj2=o2; } @Override public void run() { String name = Thread.currentThread().getName(); System.out.println(name + " acquiring lock on "+obj1); synchronized (obj1) { System.out.println(name + " acquired lock on "+obj1); work(); System.out.println(name + " acquiring lock on "+obj2); synchronized (obj2) { System.out.println(name + " acquired lock on "+obj2); work(); } System.out.println(name + " released lock on "+obj2); } System.out.println(name + " released lock on "+obj1); System.out.println(name + " finished execution."); } private void work() { try { Thread.sleep(30000); } catch (InterruptedException e) { e.printStackTrace(); } } }

All the three threads will be able to acquire a lock on the first object. But, they are using the shared resources and started in such a way that they will keep on waiting indefinitely to acquire the lock on the second object.

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