Series About Java Concurrency – Pt. 3

As it seems that even experienced Java programmers might have serious misconceptions regarding the Java memory model, I’ve decided to publish a concurrency related puzzle once again. Consider the following simple program and try to predict it’s output:

package com.wordpress.mlangc.concurrent;

public class PleaseWait
{
    private static final long MILLIS_TO_WAIT = 2500;
    private static boolean stop = false;
    
    public static void main(String[] args)
    {
        Thread timer = new Thread(new Runnable()
        {
            public void run()
            {
                try
                {
                    Thread.sleep(MILLIS_TO_WAIT);
                }
                catch(InterruptedException e)
                {
                    // We are already exiting the thread.
                }
                finally
                {
                    stop = true;
                    System.out.println("Stop requested.");
                }
            }
        });
        
        timer.start();
        
        long start = System.currentTimeMillis();
        while(!stop)
            ; // <-- Do nothing.
        
        long stoppedAfter = System.currentTimeMillis() - start;
        System.out.printf("Stopped after %dms.\n", stoppedAfter);
    }
}

The solution, together with explanations will be published in the near future.

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