Pool.java

/*
 * Copyright 2013 Hannes Janetzek
 *
 * This file is part of the OpenScienceMap project (http://www.opensciencemap.org).
 *
 * This program 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 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 Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License along with
 * this program. If not, see <http://www.gnu.org/licenses/>.
 */
package org.oscim.utils.pool;

import javax.annotation.CheckReturnValue;

@SuppressWarnings({ "rawtypes", "unchecked" })
public abstract class Pool<T extends Inlist<?>> {
	protected T mPool;
	protected int mLimit;
	protected int mFill;

	/**
	 * @param item release resources
	 * @return whether item should be added to
	 *         pool. use to manage pool size manually
	 */
	protected boolean clearItem(T item) {
		return true;
	}

	/**
	 * Release 'item' to pool.
	 * <p>
	 * Usage item = pool.release(item), to ensure to not keep a reference to
	 * item!
	 */
	@CheckReturnValue
	public T release(T item) {
		if (item == null)
			return null;

		if (!clearItem(item))
			return null;

		((Inlist) item).next = mPool;
		mPool = item;

		return null;
	}

	/**
	 * Release 'list' to pool.
	 * <p>
	 * Usage list = pool.releaseAll(list), to ensure to not keep a reference to
	 * list!
	 */
	@CheckReturnValue
	public T releaseAll(T list) {
		if (list == null)
			return null;

		while (list != null) {

			T next = (T) list.next;

			clearItem(list);

			((Inlist) list).next = mPool;
			mPool = list;

			list = next;
		}
		return null;
	}

	/** remove 'item' from 'list' and add back to pool */
	public T release(T list, T item) {
		if (item == null)
			return list;

		clearItem(item);

		return (T) Inlist.remove((Inlist) list, item);
	}

	/** get an item from pool */
	public T get() {
		if (mPool == null)
			return createItem();

		Inlist ret = mPool;
		mPool = (T) mPool.next;

		ret.next = null;
		return (T) ret;
	}

	protected abstract T createItem();
}