/*
 * JBoss, Home of Professional Open Source
 * Copyright 2005-2008, Red Hat Middleware LLC, and individual contributors
 * by the @authors tag. See the copyright.txt in the distribution for a
 * full listing of individual contributors.
 *
 * This is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation; either version 2.1 of
 * the License, or (at your option) any later version.
 *
 * This software 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 for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this software; if not, write to the Free
 * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
 * 02110-1301 USA, or see the FSF site: http://www.fsf.org.
 */ 

package org.jboss.messaging.util;

import java.util.AbstractSet;
import java.util.Iterator;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

/**
 * 
 * A ConcurrentHashSet.
 * 
 * Offers same concurrency as ConcurrentHashMap but for a Set
 * 
 * @author <a href="tim.fox@jboss.com">Tim Fox</a>
 * @version <tt>$Revision: 1935 $</tt>
 *
 * $Id: ConcurrentReaderHashSet.java 1935 2007-01-09 23:29:20Z clebert.suconic@jboss.com $
 */
public class ConcurrentHashSet<E> extends AbstractSet<E> implements ConcurrentSet<E>
{
   private ConcurrentMap<E, Object> theMap;
   
   private static final Object dummy = new Object();
   
   public ConcurrentHashSet()
   {
      theMap = new ConcurrentHashMap<E, Object>();
   }
   
   public int size()
   {
      return theMap.size();
   }
   
   public Iterator<E> iterator()
   {
      return theMap.keySet().iterator();
   }
   
   public boolean isEmpty()
   {
      return theMap.isEmpty();
   }
   
   public boolean add(E o)
   {
      return theMap.put(o, dummy) == null;
   }
   
   public boolean contains(Object o)
   {
      return theMap.containsKey(o);
   }
   
   public void clear()
   {
      theMap.clear();
   }
   
   public boolean remove(Object o)
   {
      return theMap.remove(o) == dummy;
   }
   
   public boolean addIfAbsent(E o)
   {
   	Object obj = theMap.putIfAbsent(o, dummy);
   	
   	return obj == null;
   }

}