FULL PRODUCT VERSION :
java version "1.5.0_06"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_06-b05)
Java HotSpot(TM) Client VM (build 1.5.0_06-b05, mixed mode, sharing)

FULL OS VERSION :
Microsoft Windows XP [Version 5.1.2600]

EXTRA RELEVANT SYSTEM CONFIGURATION :
Single Dual-Core Pentium 4.
Dell Dimension DIM4700

The dual-core seems to matter.

A DESCRIPTION OF THE PROBLEM :
Running two threads, one of which creates a lot of garbage, results in almost no CPU allocated to either thread. I cannot find evidence that the machine is in any way busy, in particular, the disk is not working.

Running a single thread that creates a lot of garbage gives the same behavior when -Xincgc is specified.

This may be related to dual-core technology. I have not tried this on enough machines to know for sure.

THE PROBLEM WAS REPRODUCIBLE WITH -Xint FLAG: No

THE PROBLEM WAS REPRODUCIBLE WITH -server FLAG: Did not try

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run the attached code and look at the Windows Task Manager. CPU is near zero.

Alternatively, don't start Thread t but instead use -Xincgc. Same phenomenon.


EXPECTED VERSUS ACTUAL BEHAVIOR :
Expected 100% CPU utilization. Got near-zero.


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------

import java.util.*;

class Test1 {


   public static void main(String[] args) {
      Thread t = new Thread(new Run());
      t.start();
      
      Thread t2 = new Thread(new Junk());
      t2.start();
   }
   
   private static class Junk implements Runnable {
      public void run() {
         while ( true ) {
            new Integer(1);
         }
      }
   }

   private static class Run implements Runnable {
      public void run() {
         long t1 = System.currentTimeMillis();
         for (int j=0; j < 10000; j++) {
            for (int k=0; k < 1000000; k++) {
            }
         }
         long t2 = System.currentTimeMillis();
         System.out.println("Done: " + (t2-t1));
      }
   }

}
---------- END SOURCE ----------