IDRef.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 IDRef {
    private static Map<Object, WRef> map = new HashMap<Object, WRef>();
    private static ReferenceQueue<IDRef> queue = new ReferenceQueue<IDRef>();
    private static int nextseq = 0;
    /* Just for debugging */
    private final Object val;
    private final int seq;
    
    private IDRef(Object val) {
	synchronized(IDRef.class) {
	    this.seq = nextseq++;
	}
	this.val = val;
    }
    
    private static class WRef extends WeakReference<IDRef> {
	private final Object val;
	
	private WRef(IDRef ref, Object val) {
	    super(ref, queue);
	    this.val = val;
	}
    }
    
    public static IDRef intern(Object x) {
	if(x == null)
	    return(null);
	synchronized(map) {
	    WRef old;
	    while((old = (WRef)queue.poll()) != null) {
		if(map.get(old.val) == old)
		    map.remove(old.val);
	    }
	    WRef ref = map.get(x);
	    IDRef id = (ref == null)?null:(ref.get());
	    if(id == null) {
		id = new IDRef(x);
		ref = new WRef(id, x);
		map.put(x, ref);
	    }
	    return(id);
	}
    }
    
    public String toString() {
	return("<ID: " + val + " (" + seq + ")>");
    }
}