/* XXL: The eXtensible and fleXible Library for data processing

Copyright (C) 2000-2011 Prof. Dr. Bernhard Seeger
                        Head of the Database Research Group
                        Department of Mathematics and Computer Science
                        University of Marburg
                        Germany

This library 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 3 of the License, or (at your option) any later version.

This library 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 library;  If not, see <http://www.gnu.org/licenses/>. 

    http://code.google.com/p/xxl/

*/

package xxl.core.util;

import java.util.Stack;

import xxl.core.functions.Function;

/**
 *  An object pool allows the reuse of unneeded objects by storing them in a pool.
 *  The purpose is to avoid garbage collection and recreation of commonly used objects.
 */
public class ObjectPool<E> {

	/**
 	 *  A parameterless function returning a new instance of an arbitrary object.
	 */
	protected Function<Object,E> tupleFactory;

	/**
 	 *  The maximum number of objects to be stored in the pool.
	 */
	protected int maxSize;

	/**
 	 *  The object pool internally realized by a {@link java.util.Stack Stack}.
	 */
	protected Stack<E> pool = new Stack<E>();

	/**
 	 *  Constructs a new object pool.
 	 *  @param tupleFactory A parameterless function returning a new instance of an arbitrary object.
 	 *  @param maxSize The maximum number of objects to be stored in the pool.
	 */
	public ObjectPool (Function<Object,E> tupleFactory, int maxSize) {
		this.tupleFactory = tupleFactory;
		this.maxSize = maxSize;
	}

	/**
 	 *  Sets the maximum number of objects to be stored in the pool.
 	 *  @param newMaxSize The maximum number of objects to be stored in the pool.
	 */
	public void setMaxSize(int newMaxSize) {
		maxSize = newMaxSize;
		for (int i=pool.size(); i>maxSize; i--) 
			pool.pop();
	}

	/**
 	 *  Retrieves an object from the pool if available, otherwise the result of
 	 *  <code>tupleFactory.invoke()</code> is returned.
 	 *  @return an object from the pool if available, otherwise
 	 *  <code>tupleFactory.invoke()</code>.
	 */
	public Object getObject () {
		if (pool.empty()) 
			return tupleFactory.invoke();
		return pool.pop();
	}

	/**
	 *  Delivers an object to the pool. If the maximum size of the pool is not reached,
	 *  the object is stored, otherwise it will be dropped.
 	 *  @param done The object to be delivered to the pool.
	 */
	public void releaseObject (E done) {
		if (pool.size() < maxSize) 
			pool.push(done);
	}
}