1 /* 2 * Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 */ 23 24 /** 25 * This is a helper class that forces the garbage collecting process. It 26 * attempts to consume all memory available to the young generation by 27 * creating a lot of unreferenced objects. Sooner or later the garbage 28 * collector shall be invoked. 29 * 30 * For purposes of performance the task is implemented to be ran with 31 * a small memory size less or equal to 128 megabytes. This shall be 32 * excplicitly specified with -Xmx JVM's option. In case if this option 33 * is not specified it's not guaranteed that GC will be invoked. 34 * 35 * The class is intended to be used with -Xloggc option to provide diagnostics 36 * output which can be parsed by the real tests. 37 * 38 * The class is implemented as an alternative to the explicit call to 39 * System.gc(). The second has some drawbacks and should be avoided. 40 */ 41 public class GCTask { 42 43 public static final int BLOCK_SIZE = 16 * 1024; // 16 kilobytes 44 public static final int MAX_ITERATIONS = 8192; // 16K * 8K = 128M 45 public static byte[] garbage; 46 47 @SuppressWarnings("unused") 48 public void run() { 49 // ensure there's an object that will survive garbage collecting 50 byte[] survivor = new byte[BLOCK_SIZE]; 51 52 // if -Xmx has not been specified we assume that we're working within 53 // 128 megabytes of memory 54 long iterCount = Math.min(Runtime.getRuntime().maxMemory() / BLOCK_SIZE, 55 MAX_ITERATIONS); 56 while (iterCount-- > 1) { 57 // make an object that will be eligible for garbage collecting 58 garbage = new byte[BLOCK_SIZE]; 59 } 60 } 61 62 public static void main(String[] args) { 63 new GCTask().run(); 64 } 65 66 }