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/*
 * Copyright (c) 1998-2010, Peter T Mount

 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 
 *   Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 *
 *   Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 *
 *   Neither the name of the retep.org.uk nor the names of its contributors
 *   may be used to endorse or promote products derived from this software
 *   without specific prior written permission.
 *
 * 
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER
 * OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package uk.org.retep.util.collections.queue;

import java.util.Deque;

/**
 * A Pool of reusable objects. The objects must implement the ConcurrentObjectPool.Entry
 * interface, which is called when an object is returned to the pool.
 *
 * @param  
 * @author peter
 */
public interface ObjectPool
    extends Deque
{
    /**
     * Ensure the pool contains a set number of entries. If the pool is currently
     * in use, this will continue until the moment that the pool has the required
     * number of entries.
     *
     * For example, if 1000 entries are required, and whilst the method is
     * executing, 10 entries are removed, then this method will actually create
     * 1010 entries.
     *
     * @param size The minimum size of the pool
     */
    void populatePool( int size );
    
    /**
     * Ensure the pool contains a set number of entries. If the pool is currently
     * in use, this will continue until the moment that the pool has the required
     * number of entries.
     *
     * For example, if 1000 entries are required, and whilst the method is
     * executing, 10 entries are removed, then this method will actually create
     * 1010 entries.
     *
     * @param size The minimum size of the pool
     * @param background If true, the population is performed in a background
     * Thread from
     */
    void populatePool( final int size, boolean background );
    
    /**
     * Interface implemented by an object that can be pooled.
     */
    static interface Entry
    {
        /**
         * Called when an instance is returned to the pool.
         */
        void instanceReturnedToPool();
    }
    
    /**
     * Interface implemented by a class used to create new instances of pooled
     * entries.
     */
    public static interface Factory
    {
        /**
         * @return new instance of an Entry
         * @throws Exception on error
         */
        E createInstance() throws Exception;
    }
    
}