Mega Code Archive
A bag of weakly referenced objects
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/*
* Copyright (c) 1998 - 2005 Versant Corporation
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Contributors:
* Versant Corporation - initial API and implementation
*/
import java.util.HashSet;
import java.util.List;
import java.util.ArrayList;
import java.util.Iterator;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
import java.lang.ref.Reference;
/**
* This maintains a bag of weakly referenced objects. The clean method
* must be called from time to time to get rid of the objects that the
* garbage collector wants to nuke. This class is not synchronized.
*/
public final class WeakBag {
private HashSet set = new HashSet();
private ReferenceQueue refQueue = new ReferenceQueue();
public WeakBag() {
}
/**
* Add o to the bag and return the WeakReference that can be used to
* remove it.
*/
public WeakReference add(Object o) {
WeakReference ans = new WeakReference(o, refQueue);
set.add(ans);
return ans;
}
/**
* Remove o from the bag.
*/
public void remove(Reference o) {
set.remove(o);
}
/**
* Get the approximate number of objects in the bag.
*/
public int size() {
return set.size();
}
/**
* Get all the objects still in the bag.
*/
public List values() {
ArrayList a = new ArrayList(set.size());
for (Iterator i = set.iterator(); i.hasNext(); ) {
WeakReference r = (WeakReference)i.next();
Object o = r.get();
if (o != null) a.add(o);
}
return a;
}
/**
* Get rid of objects in the bag that the garbage collector wants to
* nuke. This does not block.
*/
public void clean() {
for (;;) {
Object r = refQueue.poll();
if (r == null) return;
set.remove(r);
}
}
}
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