CountDownLatch example of a more general wait/notify mechanism

public void testWaitNotify() throws Exception {
   final Object mutex = new Object();
   Thread t = new Thread() {

public void run() {

// we must acquire the lock before waiting to be notified

synchronized(mutex) {

   System.out.println("Going to wait " +

    "(lock held by " + Thread.currentThread().getName() + ")");

try {

   mutex.wait(); // this will release the lock to be notified (optional timeout can be supplied)

} catch (InterruptedException e) {

   e.printStackTrace();

} 

System.out.println("Done waiting " +

 "(lock held by " + Thread.currentThread().getName() + ")");

   }

}
   };

   t.start(); // start her up and let her wait()

   // not normally how we do things, but good enough for demonstration purposes
   Thread.sleep(1000);

   // we acquire the lock released by wait(), and notify()
   synchronized (mutex) {

System.out.println("Going to notify " +

 "(lock held by " + Thread.currentThread().getName() + ")");

mutex.notify();

System.out.println("Done notify " +

 "(lock held by " + Thread.currentThread().getName() + ")");
   }

}

Output:

Going to wait (lock held by Thread-0) Going to notify (lock held by main) Done notify (lock held by main) Done waiting (lock held by Thread-0)

Related Article:

• Java Concurrency Tutorial – CountDownLatch

Reference: Java Concurrency Part 6 – CountDownLatch from our JCG partners at the Carfey Software blog