1 /* 2 * Copyright (c) 2014, 2018, 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 package gc.g1.unloading.keepref; 24 25 import java.lang.reflect.*; 26 import java.util.*; 27 28 /** 29 * This holder keeps class from being collected by saving link in static field of class loaded by null classloader. 30 * It uses pool of classes that should reside in bootclasspath. 31 */ 32 public class NullClassloaderHolder implements RefHolder { 33 34 private static final int NUMBER_OF_CLASSES = 1000; 35 private static Set<Class<?>> classesPool = Collections.synchronizedSet(new HashSet<Class<?>>()); 36 37 static { 38 for (int i = 1; i <= NUMBER_OF_CLASSES; i++) { 39 String className = "gc.g1.unloading.rootSetHelper.classesPool.Class" + i; 40 try { 41 Class<?> clazz = Class.forName(className); 42 if (clazz.getClassLoader() != null) { 43 throw new RuntimeException("Test bug! Classes from pool implied to be loaded by bootclassloader."); 44 } 45 classesPool.add(clazz); 46 } catch (ClassNotFoundException e) { 47 throw new RuntimeException("Test bug", e); 48 } 49 } 50 } 51 52 @Override 53 public Object hold(Object object) { 54 if (classesPool.isEmpty()) { 55 return null; 56 } else { 57 Class<?> clazz = (Class<?>) classesPool.iterator().next(); 58 classesPool.remove(clazz); 59 Field f = getRandomField(clazz); 60 try { 61 f.set(null, object); 62 return clazz.newInstance(); 63 } catch (IllegalArgumentException | IllegalAccessException | InstantiationException e) { 64 throw new RuntimeException("Test bug", e); 65 } 66 } 67 } 68 69 private static Field getRandomField(Class<?> clazz) { 70 ArrayList<Field> fields = new ArrayList<>(); 71 for (Field f : clazz.getFields()) { 72 if (f.getName().startsWith("staticField")) { 73 fields.add(f); 74 } 75 } 76 return fields.get(new Random().nextInt(fields.size())); 77 } 78 79 }