130 lines
4.1 KiB
Java
130 lines
4.1 KiB
Java
/*************************************************************************
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*
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* Copyright 2008 by Sun Microsystems, Inc.
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*
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* OpenOffice.org - a multi-platform office productivity suite
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*
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* $RCSfile: WaitUnreachable.java,v $
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* $Revision: 1.5 $
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*
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* This file is part of OpenOffice.org.
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*
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* OpenOffice.org is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Lesser General Public License version 3
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* only, as published by the Free Software Foundation.
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*
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* OpenOffice.org is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Lesser General Public License version 3 for more details
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* (a copy is included in the LICENSE file that accompanied this code).
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*
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* You should have received a copy of the GNU Lesser General Public License
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* version 3 along with OpenOffice.org. If not, see
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* <http://www.openoffice.org/license.html>
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* for a copy of the LGPLv3 License.
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*
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************************************************************************/
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package util;
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import java.lang.ref.PhantomReference;
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import java.lang.ref.ReferenceQueue;
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/**
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* Wait until an object has become unreachable.
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*
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* <p>Instances of this class will typically be used as either:</p>
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* <pre>
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* SomeType o = new SomeType(...);
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* ... // use "o"
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* WaitUnreachable u = new WaitUnreachable(o);
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* o = null;
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* u.waitUnreachable();
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* </pre>
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* <p>or:</p>
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* <pre>
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* WaitUnreachable u = new WaitUnreachable(new SomeType(...));
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* ... // use "(SomeType) u.get()"
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* u.waitUnreachable();
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* </pre>
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*/
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public final class WaitUnreachable {
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/**
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* Creates a new waiter.
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*
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* @param obj the object on which to wait
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*/
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public WaitUnreachable(Object obj) {
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this.obj = obj;
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queue = new ReferenceQueue();
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ref = new PhantomReference(obj, queue);
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}
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/**
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* Gets the object on which to wait.
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*
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* @return the object on which to wait, or <code>null</code> if
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* <code>waitUnreachable</code> has already been called
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*/
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public synchronized Object get() {
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return obj;
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}
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/**
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* Starts waiting for the object to become unreachable.
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*
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* <p>This blocks the current thread until the object has become
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* unreachable.</p>
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*
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* <p>Actually, this method waits until the JVM has <em>detected</em> that
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* the object has become unreachable. This is not deterministic, but this
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* methods makes a best effort to cause the JVM to eventually detect the
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* situation. With a typical JVM, this should suffice.</p>
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*/
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public void waitUnreachable() {
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synchronized (this) {
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obj = null;
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}
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System.out.println("waiting for gc");
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while (queue.poll() == null) {
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System.gc();
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System.runFinalization();
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byte[] dummy = new byte[1024];
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}
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}
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/**
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* Ensures that an object will be finalized as soon as possible.
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*
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* <p>This does not block the current thread. Instead, a new thread is
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* spawned that busy waits for the given object to become unreachable.</p>
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*
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* <p>This method cannot guarantee that the given object is eventually
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* finalized, but it makes a best effort. With a typical JVM, this should
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* suffice.</p>
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*
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* @param obj the object of which to ensure finalization
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*/
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public static void ensureFinalization(final Object obj) {
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final class WaitThread extends Thread {
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public WaitThread(Object obj) {
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super("ensureFinalization");
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unreachable = new WaitUnreachable(obj);
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}
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public void run() {
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unreachable.waitUnreachable();
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}
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private final WaitUnreachable unreachable;
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};
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new WaitThread(obj).start();
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}
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private Object obj;
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private final ReferenceQueue queue;
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private final PhantomReference ref;
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}
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