96 lines
3.2 KiB
Java
96 lines
3.2 KiB
Java
/*
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* Copyright (c) 2014, 2018, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package gc.g1.unloading.keepref;
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import gc.g1.unloading.check.cleanup.UnusedThreadKiller;
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/**
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* This holder prevents class from being unloaded by keeping reference in stack local.
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*
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*/
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public class InStackLocalHolder implements RefHolder {
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public static class AuxiliaryThread extends Thread {
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private static final int STACK_DEPTH = 300;
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private ReferenceHolder referenceHolder;
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public AuxiliaryThread(ReferenceHolder referenceHolder) {
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this.referenceHolder = referenceHolder;
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}
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synchronized public void finishThread() {
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notifyAll();
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}
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@Override
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synchronized public void run() {
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new A().call(referenceHolder, STACK_DEPTH);
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}
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}
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private static class A {
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public void call(ReferenceHolder holder, int stackDepth) {
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if (stackDepth > 0) {
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new A().call(holder, stackDepth - 1);
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} else {
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Object ref = holder.obtainAndClear();
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synchronized (Thread.currentThread()) {
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try {
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Thread.currentThread().wait();
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if (ref.hashCode() == 42) {
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System.out.println("This clause is made to prevent compiler and javac optimizations from eliminating local reference \"ref\".");
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}
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} catch (InterruptedException e) {
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new RuntimeException("Unexpected InterruptedException");
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}
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}
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}
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}
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}
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private static class ReferenceHolder {
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private Object reference;
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public ReferenceHolder(Object reference) {
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this.reference = reference;
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}
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public Object obtainAndClear() {
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Object returnValue = reference;
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reference = new Object();
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return returnValue;
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}
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}
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@Override
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public Object hold(Object object) {
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Thread thread = new AuxiliaryThread(new ReferenceHolder(object));
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thread.setDaemon(true);
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thread.start();
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return new UnusedThreadKiller(thread.getId());
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}
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}
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