src/org/apache/xpath/axes/IteratorPool.java

/*
 * The Apache Software License, Version 1.1
 *
 *
 * Copyright (c) 1999-2003 The Apache Software Foundation.  All rights 
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer. 
 *
 * 2. 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.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:  
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
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 * 4. The names "Xalan" and "Apache Software Foundation" must
 *    not be used to endorse or promote products derived from this
 *    software without prior written permission. For written 
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 *
 * 5. Products derived from this software may not be called "Apache",
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 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
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 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation and was
 * originally based on software copyright (c) 1999, Lotus
 * Development Corporation., http://www.lotus.com.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */
package org.apache.xpath.axes;

import java.util.Vector;

import org.apache.xml.dtm.DTMIterator;
import org.apache.xml.utils.WrappedRuntimeException;

/**
 * Pool of object of a given type to pick from to help memory usage
 * @xsl.usage internal
 */
public class IteratorPool implements java.io.Serializable
{

  /** Type of objects in this pool.
   *  @serial          */
  private final DTMIterator m_orig;

  /** Vector of given objects this points to.
   *  @serial          */
  private final Vector m_freeStack;

  /**
   * Constructor IteratorPool
   *
   * @param original The original iterator from which all others will be cloned.
   */
  public IteratorPool(DTMIterator original)
  {
    m_orig = original;
    m_freeStack = new Vector();
  }
  
  /**
   * Get an instance of the given object in this pool 
   *
   * @return An instance of the given object
   */
  public synchronized DTMIterator getInstanceOrThrow()
    throws CloneNotSupportedException
  {
    // Check if the pool is empty.
    if (m_freeStack.isEmpty())
    {

      // Create a new object if so.
      return (DTMIterator)m_orig.clone();
    }
    else
    {
      // Remove object from end of free pool.
      DTMIterator result = (DTMIterator)m_freeStack.lastElement();

      m_freeStack.setSize(m_freeStack.size() - 1);

      return result;
    }
  }
  
  /**
   * Get an instance of the given object in this pool 
   *
   * @return An instance of the given object
   */
  public synchronized DTMIterator getInstance()
  {
    // Check if the pool is empty.
    if (m_freeStack.isEmpty())
    {

      // Create a new object if so.
      try
      {
        return (DTMIterator)m_orig.clone();
      }
      catch (Exception ex)
      {
        throw new WrappedRuntimeException(ex);
      }
    }
    else
    {
      // Remove object from end of free pool.
      DTMIterator result = (DTMIterator)m_freeStack.lastElement();

      m_freeStack.setSize(m_freeStack.size() - 1);

      return result;
    }
  }

  /**
   * Add an instance of the given object to the pool  
   *
   *
   * @param obj Object to add.
   */
  public synchronized void freeInstance(DTMIterator obj)
  {
    m_freeStack.addElement(obj);
  }
}