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JBullet - Java port of Bullet Physics Library
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/*
 * Java port of Bullet (c) 2008 Martin Dvorak 
 *
 * Bullet Continuous Collision Detection and Physics Library
 * Copyright (c) 2003-2008 Erwin Coumans  http://www.bulletphysics.com/
 *
 * This software is provided 'as-is', without any express or implied warranty.
 * In no event will the authors be held liable for any damages arising from
 * the use of this software.
 * 
 * Permission is granted to anyone to use this software for any purpose, 
 * including commercial applications, and to alter it and redistribute it
 * freely, subject to the following restrictions:
 * 
 * 1. The origin of this software must not be misrepresented; you must not
 *    claim that you wrote the original software. If you use this software
 *    in a product, an acknowledgment in the product documentation would be
 *    appreciated but is not required.
 * 2. Altered source versions must be plainly marked as such, and must not be
 *    misrepresented as being the original software.
 * 3. This notice may not be removed or altered from any source distribution.
 */

package com.bulletphysics.util;

import java.util.HashMap;
import java.util.Map;

/**
 * Object pool.
 * 
 * @author jezek2
 */
public class ObjectPool {
	
	private Class cls;
	private ObjectArrayList list = new ObjectArrayList();
	
	public ObjectPool(Class cls) {
		this.cls = cls;
	}

	private T create() {
		try {
			return cls.newInstance();
		}
		catch (InstantiationException e) {
			throw new IllegalStateException(e);
		}
		catch (IllegalAccessException e) {
			throw new IllegalStateException(e);
		}
	}
	
	/**
	 * Returns instance from pool, or create one if pool is empty.
	 * 
	 * @return instance
	 */
	public T get() {
		if (list.size() > 0) {
			return list.remove(list.size() - 1);
		}
		else {
			return create();
		}
	}
	
	/**
	 * Release instance into pool.
	 * 
	 * @param obj previously obtained instance from pool
	 */
	public void release(T obj) {
		list.add(obj);
	}
	
	////////////////////////////////////////////////////////////////////////////
	
	private static ThreadLocal threadLocal = new ThreadLocal() {
		@Override
		protected Map initialValue() {
			return new HashMap();
		}
	};
	
	/**
	 * Returns per-thread object pool for given type, or create one if it doesn't exist.
	 * 
	 * @param cls type
	 * @return object pool
	 */
	@SuppressWarnings("unchecked")
	public static  ObjectPool get(Class cls) {
		Map map = threadLocal.get();
		
		ObjectPool pool = (ObjectPool)map.get(cls);
		if (pool == null) {
			pool = new ObjectPool(cls);
			map.put(cls, pool);
		}
		
		return pool;
	}

	public static void cleanCurrentThread() {
		threadLocal.remove();
	}

}