Help with a simple code snippet?

Question

Can someone tell me where I'm going wrong with this bit of code? Its more or less derrived from the Java tutorials, though its mid chapter so lets you make your own mind up about the surrounding code...I'm just trying to get a grip on how notifyAll() and wait() work(). The WaitProcess is suposed to sit there and wait for the NotifyProcess to wake it up. I was expecting both processes to finish after the notifyAll().
Thanks for any help...
Steve
public class NotifyWaitTest {
    static boolean waiting = true;
    static class WaitProcess implements Runnable {
        public void run() {
            System.out.println("WaitProcess: started and waiting");
            waitHere();
            System.out.println("WaitProcess: Finished");
        public synchronized void waitHere() {
            while(waiting)
                try {
                    wait();
                } catch(InterruptedException e) {
    static class NotifyProcess implements Runnable {
        public void run() {
            System.out.println("NotifyProcess: started and sleeping 10s");
            try {
                Thread.sleep(10000);
            } catch(InterruptedException e) {  
            notifyWait();
        public synchronized void notifyWait() {
            waiting = false;
            notifyAll();
            System.out.println("NotifyProcess: waiting = false, notifyAll()");
    public static void main(String... args) {
        new Thread(new WaitProcess()).start();
        new Thread(new NotifyProcess()).start();
}Message was edited by:
Steve12345

Answer 1

The object you are waiting on and the object you are
notifying are different.
I thought notifyAll() interrupted all threads?No. notifyAll is an instance method (and wait is instance method too) and wakes up only threads, that waits on that object (instance) beeing notified. In your code call
notifyAll();is actually the same, as
this.notifyAll();which is notification of objects, that waits on notifying object (but not all waiting threads).
All synchronization in java is tied to particular instances and is not a "global synchronization". This means, that two threads can simultaneously hold locks (or, other words, execute sections inside synchronized statements), but only on different instances. Lock on the particular instance can be hold by an only one thread at a time. Waiting and notifications are also tied to instances and requires a lock on the used object (i.e. should be executed in the synchronized block for that object). In your code syncronization is performed on different instances: one on the instance of WaitProcess (and wait is preformed on this instance), and second is performed on the instance of NotifyProcess (and notifyAll is performed on this instance). You should use synchonized section in both classes, and this synchonized section should be invoked on the same instance (not on two instances of same class).
P.S. "interrupted" is wrong word here. notifyAll() "wakes up" threads, which waits on particular lock, allowing them to continue their execution. But "interrupt" means setting "interrupted" flag or throwing InterruptedException (which is abrupt completion of wait method).