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 gc.g1.unloading.bytecode.BytecodeMutatorFactory; 26 import gc.g1.unloading.bytecode.TemplateClassWithStaticField; 27 import gc.g1.unloading.classloaders.DoItYourselfClassLoader; 28 29 import java.lang.reflect.InvocationTargetException; 30 import java.lang.reflect.Method; 31 import java.util.concurrent.atomic.AtomicLong; 32 33 /** 34 * This holder prevents class from being collected by keeping link in static field of another class. 35 * 36 */ 37 public class InStaticFieldHolder implements RefHolder { 38 39 private static BytecodeMutatorFactory bm = new BytecodeMutatorFactory(TemplateClassWithStaticField.class.getName()); 40 41 private static final String CLASS_NAME_BASE = "StaticFieldHolder_"; 42 43 private static AtomicLong counter = new AtomicLong(0); 44 45 @Override 46 public Object hold(Object object) { 47 try { 48 String className = bm.padName(CLASS_NAME_BASE + counter.getAndIncrement()); 49 byte[] bytecode = bm.getBytecode(className); 50 DoItYourselfClassLoader loader = new DoItYourselfClassLoader(); 51 Class<?> clazz = loader.defineClass(className, bytecode); 52 for (Method m : clazz.getMethods()) { 53 if ("setField".equals(m.getName())) { 54 m.invoke(null, object); 55 } 56 } 57 Object instance = clazz.newInstance(); 58 return instance; 59 } catch (InstantiationException | IllegalAccessException | IllegalArgumentException | InvocationTargetException e) { 60 throw new RuntimeException("Something went wrong in StaticFieldHolder ", e); 61 } 62 } 63 64 }