static volatile boolean - thread not getting terminated

Question

I wrote simple multithreaded application, just to play around with concurrency but I have a problem with boolean variable which controles the loop in thread. One of the functions should stop the thread if there's noelements left in queue and I guess that is my problem because If I add something in between braces to:

while (!queue.isEmpty()) {
}
isRunning = false;

So it becomes :

while (!queue.isEmpty()) {
    System.out.println("ASD");
}
isRunning = false;

It is working a bit better - the program terminates after executing turnOff method

Any Ideas?

Here is full code of my app:

package test;

public class xxx {
    public static void main(String[] args) {
        Foo instance = Foo.getInstance();
        Thread x = new Thread(instance);
        x.start();

        for (int count = 1; count < 100000; count++)
            instance.addToQueue(count + "");
        instance.turnOff();
    }
}

And:

package test;

import java.util.LinkedList;
import java.util.List;

public class Foo implements Runnable {
    private static Foo inner = null;
    private static List<String> queue = new LinkedList<String>();
    private volatile static boolean isRunning = false;

    private Foo() { }

    public static Foo getInstance() {
        if (inner == null) {
            inner = new Foo();
        }
        return inner;
    }

    public void addToQueue(String toPrint) {
        synchronized (queue) {
            queue.add(toPrint);
        }

    }

    public void removeFromQueue(String toRemove) {
        synchronized (queue) {
            queue.remove(toRemove);
        }
    }

    public void turnOff() {
        while (!queue.isEmpty()) {
        }
        System.out.println("end");
        isRunning = false;
    }

    @Override
    public void run() {
        isRunning = true;
        while (isRunning) {
            if (!queue.isEmpty()) {
                String string = queue.get(0);
                System.out.println(string);
                removeFromQueue(string);
            }

        }
    }
}

Answer 1

It is a race condition problem. Possibly the run method (the other thread) is executed after the turnOff in in the main thread so the flag isRunning is set as true again and the loop never ends.

That would explain why with a simple System.out.println("ASD") becomes better: the isRunning=false is delayed.