I'm trying to build an application that will use multiple cores
efficiently, but I'm running into to some difficulties.  I've written a
simple small example to demonstrate the problem and attached it below.
When I run this program on my dual core computer I expect that both cores
should be actively running wasteTime() and my CPU utilization should be
nearly 100% on both, but this isn't the result I'm getting.  A single CPU
is maxed out and the other one is sitting idle.  This isn't what I want
for obvious reasons.  

Can any explain to me why this is happening and what to do about it?

I know that one can fiddle with the amount of work done by each thread and
get it to behave correctly, but I don't know why it isn't behaving
correctly without this tweaking of parameters.

Thanks.

---
/*
* Main.java
*
* Created on Sep 27, 2007, 4:57:59 AM
*
* To change this template, choose Tools | Templates
* and open the template in the editor.
*/

package threadtester;

import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;

/**
*
* @author kt
*/
public class Main {

   /**
    * @param args the command line arguments
    */
   public static void main(String[] args) {
       while (true) {
           int threads = 2;

           ExecutorService executorService =
                   Executors.newFixedThreadPool(threads);

           Future[] futures = new Future[10000];
           for (int index = 0; index < 100; index++) {
               final int indexFinal = index;
               futures[index] = executorService.submit(new Callable() {
                   public Object call() throws Exception {
                       return new Double(wasteTime());
                   }
               });
           }

           executorService.shutdown();
           boolean tryAgain = false;
           do {
               try {
                   tryAgain = false;
                   executorService.awaitTermination(Long.MAX_VALUE, TimeUnit.DAYS);
               } catch (InterruptedException ex) {
                   tryAgain = true;
               }
           } while (tryAgain);        
       }
   }
   
   
   public static double wasteTime() {
       double sum = 0.0;
       for (int index = 0; index < 100; index++) {
           sum += Math.cos(index / 1000.0);
       }
       return sum;
   }

}