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/*************************************************************************
*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* Copyright 2008 by Sun Microsystems, Inc.
*
* OpenOffice.org - a multi-platform office productivity suite
*
* $RCSfile: WaitUnreachable.java,v $
* $Revision: 1.5 $
*
* This file is part of OpenOffice.org.
*
* OpenOffice.org is free software: you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License version 3
* only, as published by the Free Software Foundation.
*
* OpenOffice.org 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 Lesser General Public License version 3 for more details
* (a copy is included in the LICENSE file that accompanied this code).
*
* You should have received a copy of the GNU Lesser General Public License
* version 3 along with OpenOffice.org. If not, see
* <http://www.openoffice.org/license.html>
* for a copy of the LGPLv3 License.
*
************************************************************************/
package util;
import java.lang.ref.PhantomReference;
import java.lang.ref.ReferenceQueue;
/**
* Wait until an object has become unreachable.
*
* <p>Instances of this class will typically be used as either:</p>
* <pre>
* SomeType o = new SomeType(...);
* ... // use "o"
* WaitUnreachable u = new WaitUnreachable(o);
* o = null;
* u.waitUnreachable();
* </pre>
* <p>or:</p>
* <pre>
* WaitUnreachable u = new WaitUnreachable(new SomeType(...));
* ... // use "(SomeType) u.get()"
* u.waitUnreachable();
* </pre>
*/
public final class WaitUnreachable {
/**
* Creates a new waiter.
*
* @param obj the object on which to wait
*/
public WaitUnreachable(Object obj) {
this.obj = obj;
queue = new ReferenceQueue();
ref = new PhantomReference(obj, queue);
}
/**
* Gets the object on which to wait.
*
* @return the object on which to wait, or <code>null</code> if
* <code>waitUnreachable</code> has already been called
*/
public synchronized Object get() {
return obj;
}
/**
* Starts waiting for the object to become unreachable.
*
* <p>This blocks the current thread until the object has become
* unreachable.</p>
*
* <p>Actually, this method waits until the JVM has <em>detected</em> that
* the object has become unreachable. This is not deterministic, but this
* methods makes a best effort to cause the JVM to eventually detect the
* situation. With a typical JVM, this should suffice.</p>
*/
public void waitUnreachable() {
synchronized (this) {
obj = null;
}
System.out.println("waiting for gc");
while (queue.poll() == null) {
System.gc();
System.runFinalization();
byte[] dummy = new byte[1024];
}
}
/**
* Ensures that an object will be finalized as soon as possible.
*
* <p>This does not block the current thread. Instead, a new thread is
* spawned that busy waits for the given object to become unreachable.</p>
*
* <p>This method cannot guarantee that the given object is eventually
* finalized, but it makes a best effort. With a typical JVM, this should
* suffice.</p>
*
* @param obj the object of which to ensure finalization
*/
public static void ensureFinalization(final Object obj) {
final class WaitThread extends Thread {
public WaitThread(Object obj) {
super("ensureFinalization");
unreachable = new WaitUnreachable(obj);
}
public void run() {
unreachable.waitUnreachable();
}
private final WaitUnreachable unreachable;
};
new WaitThread(obj).start();
}
private Object obj;
private final ReferenceQueue queue;
private final PhantomReference ref;
}
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