/*
 * Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

/**
 * This is a helper class that forces the garbage collecting process. It
 * attempts to consume all memory available to the young generation by
 * creating a lot of unreferenced objects. Sooner or later the garbage
 * collector shall be invoked.
 *
 * For purposes of performance the task is implemented to be ran with 
 * a small memory size less or equal to 128 megabytes. This shall be
 * excplicitly specified with -Xmx JVM's option. In case if this option
 * is not specified it's not guaranteed that GC will be invoked.
 *
 * The class is intended to be used with -Xloggc option to provide diagnostics
 * output which can be parsed by the real tests.
 *
 * The class is implemented as an alternative to the explicit call to 
 * System.gc(). The second has some drawbacks and should be avoided.
 */
public class GCTask {
    
    public static final int BLOCK_SIZE = 16 * 1024; // 16 kilobytes
    public static final int MAX_ITERATIONS = 8192; // 16K * 8K = 128M
    public static byte[] garbage;

    @SuppressWarnings("unused")
    public void run() {
        // ensure there's an object that will survive garbage collecting
        byte[] survivor = new byte[BLOCK_SIZE];

        // if -Xmx has not been specified we assume that we're working within
        // 128 megabytes of memory
        long iterCount = Math.min(Runtime.getRuntime().maxMemory() / BLOCK_SIZE,
            MAX_ITERATIONS);
        while (iterCount-- > 1) {
            // make an object that will be eligible for garbage collecting
            garbage = new byte[BLOCK_SIZE];
        }
    }
    
    public static void main(String[] args) {
        new GCTask().run();
    }

}