simple java garbage collector torture test

GCTest.java

/*
 * in this directory:
 *   to build: 
 *    javac -Xlint:all GCTest.java
 *
 *   to run: 
 *    java -verbose:gc -server -Xincgc -Xmx1024m -classpath . GCTest
 * 
 */

import java.util.Random;

class GCTest {

  final class GCTestParams {
    static final int DEFAULT_MAX_BUCKET_SIZE  = 512;
    static final int DEFAULT_NUM_BUCKET_COUNT = 4096;
    static final int DEFAULT_NUM_ITERATIONS   = -1;

    final int maxBucketSize;
    final int maxBucketCount;
    final int numIterations;

    public GCTestParams() {
      this(
        DEFAULT_MAX_BUCKET_SIZE,
        DEFAULT_NUM_BUCKET_COUNT,
        DEFAULT_NUM_ITERATIONS);
    }

    public GCTestParams(int _maxBucketSize) {
      this(
        _maxBucketSize,
        DEFAULT_NUM_BUCKET_COUNT,
        DEFAULT_NUM_ITERATIONS);
    }

    public GCTestParams(
      int _maxBucketSize,
      int _maxBucketCount) {
        this(
          _maxBucketSize,
          _maxBucketCount,
          DEFAULT_NUM_ITERATIONS);
    }

    public GCTestParams(
      int _maxBucketSize,
      int _maxBucketCount,
      int _numIterations) {
        maxBucketSize = _maxBucketSize;
        maxBucketCount = _maxBucketCount;
        numIterations = _numIterations;
    }

    public String toString() {
      return
        "max size: " + maxBucketSize + "\n" +
        "max count: " + maxBucketCount + "\n" +
        "max iterations: " + numIterations;
    }
  }

  final GCTestParams params;

  public GCTest(String args[]) {
    params = parseArgs(args);
  }

  public GCTestParams parseArgs(String args[]) {
    try {
      switch(args.length) {
        case 3:
          return new GCTestParams(
            Integer.parseInt(args[0]),
            Integer.parseInt(args[1]),
            Integer.parseInt(args[2]));
 
        case 2:
          return new GCTestParams(
            Integer.parseInt(args[0]),
            Integer.parseInt(args[1]));

        case 1:
          return new GCTestParams(Integer.parseInt(args[0]));

        case 0:
          return new GCTestParams();

        default:
          System.err.println("invalid number of args, [0-3]");
          System.exit(1);
          return null;
      }
    } catch( NumberFormatException nfe ) {
       System.err.println("invalid arg format, [ints required]");
       System.exit(1);
       return null;
    }
  }

  public void runTest() {
    Random LCG = new Random();
    Runtime runtime = Runtime.getRuntime();
    byte [][] buckets = new byte[params.maxBucketCount][];

    System.out.println( "starting with params: " + params);

    for(int i = 0;
      params.numIterations == -1 || i < params.numIterations;
      ++i) {
        final int selectedBucket = LCG.nextInt(params.maxBucketCount);
        final int requestedBytes = LCG.nextInt(params.maxBucketSize)+1;

        System.out.println(
          "r in b[" + selectedBucket +
          "] for " + requestedBytes);

        buckets[selectedBucket ] = new byte[requestedBytes];

        System.out.println(
          " heap is now " +
          ((float)runtime.freeMemory()/runtime.maxMemory()*100.0) + "% full");
    }
  }

  public static void main(String args[]) {
    GCTest gct = new GCTest(args);
    gct.runTest();
  }
}