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/*
* Copyright (c) 2014, 2020, 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.
*/
package gc.g1.unloading.keepref;
import java.lang.reflect.*;
import java.util.*;
/**
* This holder keeps class from being collected by saving link in static field of class loaded by null classloader.
* It uses pool of classes that should reside in bootclasspath.
*/
public class NullClassloaderHolder implements RefHolder {
private static final int NUMBER_OF_CLASSES = 1000;
private static Set<Class<?>> classesPool = Collections.synchronizedSet(new HashSet<Class<?>>());
private final Random random;
static {
for (int i = 1; i <= NUMBER_OF_CLASSES; i++) {
String className = "gc.g1.unloading.rootSetHelper.classesPool.Class" + i;
try {
Class<?> clazz = Class.forName(className);
if (clazz.getClassLoader() != null) {
throw new RuntimeException("Test bug! Classes from pool implied to be loaded by bootclassloader.");
}
classesPool.add(clazz);
} catch (ClassNotFoundException e) {
throw new RuntimeException("Test bug", e);
}
}
}
public NullClassloaderHolder(long seed) {
random = new Random(seed);
}
@Override
public Object hold(Object object) {
if (classesPool.isEmpty()) {
return null;
} else {
Class<?> clazz = (Class<?>) classesPool.iterator().next();
classesPool.remove(clazz);
Field f = getRandomField(clazz);
try {
f.set(null, object);
return clazz.newInstance();
} catch (IllegalArgumentException | IllegalAccessException | InstantiationException e) {
throw new RuntimeException("Test bug", e);
}
}
}
private Field getRandomField(Class<?> clazz) {
ArrayList<Field> fields = new ArrayList<>();
for (Field f : clazz.getFields()) {
if (f.getName().startsWith("staticField")) {
fields.add(f);
}
}
return fields.get(random.nextInt(fields.size()));
}
}
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