Performance bug in and XXS patch for Parallel Old GC scanning large object arrays (original) (raw)

Wed Mar 2 12:26:44 UTC 2016

private static final long MB = 1 << 20;
private int arraySize;
private int treeDepth;
private int iterations;
private LittleTree[] arrayOfSmallTrees;

public static void main(String[] args) {
    TestLargeObjectArray test = new TestLargeObjectArray();
    test.parseCmdLine(args);
    test.buildLargeArrayOfSmallTrees();
    test.run();
}

private void run() {
    while (iterations-- > 0) {
        long start = System.currentTimeMillis();
        message("Calling System.gc()");
        System.gc();
        long end = System.currentTimeMillis();
        heapStats();
        message("Full GC duration: " + (end - start) + " ms");
    }
}

public void buildLargeArrayOfSmallTrees() {
    try {
        message("Building large array with " + arraySize + " elements of small trees with depth " + treeDepth);
        heapStats();
        arrayOfSmallTrees = new LittleTree[arraySize];
        for (int i = 0; i < arraySize; i++) {
            arrayOfSmallTrees[i] = LittleTree.build(treeDepth);
        }
        message("done");
        heapStats();
    } catch (OutOfMemoryError oom) {
        arrayOfSmallTrees = null;
        message("OutOfMemory: please reduce array size or tree depth");
        System.exit(1);
    }
}

private void heapStats() {
    long free = Runtime.getRuntime().freeMemory();
    long max = Runtime.getRuntime().maxMemory();
    float freePercentage = round((float) free / (float) max * 100);
    message("Heap stats: free:" + free / MB + " MB (" + freePercentage + " %)" + "  max:" + max / MB + " MB");
}

private float round(float f) {
    return Math.round(f * 10) / 10f;
}

private void parseCmdLine(String[] args) {
    if (args.length != 3) {
        message();
        message("usage: java " + TestLargeObjectArray.class.getName()
                + " <test iterations, e.g. 20> <large array size, e.g. 50000> <small tree depth, e.g. 4>");
        message();
        System.exit(1);
    }
    int i = 0;
    iterations = Integer.parseInt(args[i++]);
    arraySize = Integer.parseInt(args[i++]);
    treeDepth = Integer.parseInt(args[i++]);
}

private void message(String msg) {
    System.out.println(msg);
}

private void message() {
    System.out.println();
}

Performance bug in and XXS patch for Parallel Old GC scanning large object arrays (original) (raw)

Benchmark Run 1 without the path

Benchmark Run 2 without the path

Benchmark source code