| /* |
| * Copyright (c) 2014, 2018, 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 gc.g1.unloading.check.cleanup.UnusedThreadKiller; |
| |
| /** |
| * This holder prevents class from being unloaded by keeping reference in stack local. |
| * |
| */ |
| public class InStackLocalHolder implements RefHolder { |
| |
| public static class AuxiliaryThread extends Thread { |
| private static final int STACK_DEPTH = 300; |
| |
| private ReferenceHolder referenceHolder; |
| |
| public AuxiliaryThread(ReferenceHolder referenceHolder) { |
| this.referenceHolder = referenceHolder; |
| } |
| |
| synchronized public void finishThread() { |
| notifyAll(); |
| } |
| |
| @Override |
| synchronized public void run() { |
| new A().call(referenceHolder, STACK_DEPTH); |
| } |
| } |
| |
| private static class A { |
| public void call(ReferenceHolder holder, int stackDepth) { |
| if (stackDepth > 0) { |
| new A().call(holder, stackDepth - 1); |
| } else { |
| Object ref = holder.obtainAndClear(); |
| synchronized (Thread.currentThread()) { |
| try { |
| Thread.currentThread().wait(); |
| if (ref.hashCode() == 42) { |
| System.out.println("This clause is made to prevent compiler and javac optimizations from eliminating local reference \"ref\"."); |
| } |
| } catch (InterruptedException e) { |
| new RuntimeException("Unexpected InterruptedException"); |
| } |
| } |
| } |
| } |
| } |
| |
| private static class ReferenceHolder { |
| private Object reference; |
| |
| public ReferenceHolder(Object reference) { |
| this.reference = reference; |
| } |
| |
| public Object obtainAndClear() { |
| Object returnValue = reference; |
| reference = new Object(); |
| return returnValue; |
| } |
| |
| } |
| |
| @Override |
| public Object hold(Object object) { |
| Thread thread = new AuxiliaryThread(new ReferenceHolder(object)); |
| thread.setDaemon(true); |
| thread.start(); |
| return new UnusedThreadKiller(thread.getId()); |
| } |
| |
| } |