Simple program to produce "promotion failed" GC

gistfile1.java

/**
 * Simple program to produce "promotion failed" garbage collection on Oracle
 * Java VM. For JDK 1.6, please execute with following extended options.
 * 
 * java -XX:+UseConcMarkSweepGC -XX:+CMSIncrementalMode -XX:ParallelGCThreads=8
 * -Xmx32m -XX:NewSize=20m -XX:MaxNewSize=20m -server -verbose:gc
 * -XX:+PrintGCDetails -XX:+PrintGCDateStamps PromFailed
*/
public class PromFailed {
  private static class Watchdog extends Thread {
    @Override
    public void run(){
      while(true){
        try {
          long tm = System.nanoTime();
          sleep(100);
          long millis = (System.nanoTime() - tm) / 1000 / 1000;
          if(millis >= 1000){   // alert over 1sec freeze
            System.out.printf("*** app frozen %.2fsec ***%n", millis/1000.0);
          }
        } catch(InterruptedException ex){
          break;
        } catch(OutOfMemoryError ex){
          System.out.println("OOME caught in watchdog");
        }
      }
      return;
    }
  }
  public static void main(String[] args){
    new Watchdog().start();

    // calculate block count
    final long max = Runtime.getRuntime().maxMemory();
    final int size = 10;                        // size of 1 block
    final int count = (int)(max / (size + 4));  // available block count
    System.out.printf("size=%,dB, total=%,dkB, %,d blocks%n", size, max/1024, count);

    byte[][] blocks = new byte[count][];
    while(true){

      // cleanup all blocks
      java.util.Arrays.fill(blocks, null);
      System.gc();
      System.out.println("cleanup -------------");

      // allocate blocks
      try {
        for(int i=0; i<blocks.length; i++){
          blocks[i] = new byte[size];
        }
        System.out.println("fill blocks without OOME!");
      } catch(OutOfMemoryError ex){
        // cannot output message because heap is used fully.
        // System.oui.println("fill memory");
      }

      // free event-indexed block
      for(int i=0; i<blocks.length; i+=2){
        blocks[i] = null;
      }

      // double-size block allocate to even-index
      try {
        for(int i=0; i<blocks.length; i+=2){
          blocks[i] = new byte[size * 2];
        }
      } catch(OutOfMemoryError ex){/* */}
    }
  }
}