WeakList.java

/*
 *  This file is part of the Haven & Hearth game client.
 *  Copyright (C) 2009 Fredrik Tolf <fredrik@dolda2000.com>, and
 *                     Björn Johannessen <johannessen.bjorn@gmail.com>
 *
 *  Redistribution and/or modification of this file is subject to the
 *  terms of the GNU Lesser General Public License, version 3, as
 *  published by the Free Software Foundation.
 *
 *  This program 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 for more details.
 *
 *  Other parts of this source tree adhere to other copying
 *  rights. Please see the file `COPYING' in the root directory of the
 *  source tree for details.
 *
 *  A copy the GNU Lesser General Public License is distributed along
 *  with the source tree of which this file is a part in the file
 *  `doc/LPGL-3'. If it is missing for any reason, please see the Free
 *  Software Foundation's website at <http://www.fsf.org/>, or write
 *  to the Free Software Foundation, Inc., 59 Temple Place, Suite 330,
 *  Boston, MA 02111-1307 USA
 */

package haven;

import java.util.*;
import java.lang.ref.*;

public class WeakList<T> extends AbstractCollection<T> {
    private final ReferenceQueue<T> cleanq = new ReferenceQueue<T>();
    private Entry<T> head = null;

    private void clean() {
	Reference<? extends T> ref;
	while((ref = cleanq.poll()) != null) {
	    Entry e = (Entry)ref;
	    e.unlink();
	}
    }

    public Iterator<T> iterator() {
	clean();
	return(new Iterator<T>() {
		Entry<T> c = head, l = null;
		T n = null;

		public boolean hasNext() {
		    while(n == null) {
			if(c == null)
			    return(false);
			n = (l = c).get();
			c = c.n;
		    }
		    return(true);
		}

		public T next() {
		    if(!hasNext())
			throw(new NoSuchElementException());
		    T ret = n;
		    n = null;
		    return(ret);
		}

		public void remove() {
		    if(l == null)
			throw(new IllegalStateException());
		    l.unlink();
		    l = null;
		}
	    });
    }

    public Entry<T> add2(T e) {
	clean();
	Entry<T> n = new Entry<T>(e, this);
	n.link();
	return(n);
    }

    public boolean add(T e) {
	add2(e);
	return(true);
    }

    public void clear() {
	head = null;
    }

    public int size() {
	int ret = 0;
	for(T e : this)
	    ret++;
	return(ret);
    }

    public static class Entry<E> extends WeakReference<E> {
	private Entry<E> n, p;
	private WeakList<E> l;

	private Entry(E e, WeakList<E> l) {
	    super(e, l.cleanq);
	    this.l = l;
	}

	private void link() {
	    this.n = l.head;
	    if(l.head != null)
		l.head.p = this;
	    l.head = this;
	}

	private void unlink() {
	    if(this.n != null)
		this.n.p = this.p;
	    if(this.p != null)
		this.p.n = this.n;
	    if(l.head == this)
		l.head = this.n;
	    this.n = this.p = null;
	}

	public void remove() {
	    if(l == null)
		throw(new IllegalStateException());
	    unlink();
	    l = null;
	}
    }
}