content: /*
   * Copyright (c) 2001-2008 Caucho Technology, Inc.  All rights reserved.
   *
   * The Apache Software License, Version 1.1
   *
   * 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 acknowlegement:
   *       "This product includes software developed by the
   *        Caucho Technology (http://www.caucho.com/)."
   *    Alternately, this acknowlegement may appear in the software itself,
   *    if and wherever such third-party acknowlegements normally appear.
   *
   * 4. The names "Burlap", "Resin", and "Caucho" must not be used to
   *    endorse or promote products derived from this software without prior
   *    written permission. For written permission, please contact
   *    info@caucho.com.
   *
   * 5. Products derived from this software may not be called "Resin"
   *    nor may "Resin" appear in their names without prior written
   *    permission of Caucho Technology.
   *
   * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED 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 CAUCHO TECHNOLOGY OR ITS 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.
   *
   * @author Scott Ferguson
   */
  
  package com.caucho.hessian.util;
  
  import java.util.concurrent.atomic.AtomicInteger;
  import java.util.concurrent.atomic.AtomicReferenceArray;
  
  /**
   * FreeList provides a simple class to manage free objects.  This is useful
   * for large data structures that otherwise would gobble up huge GC time.
   *
   * <p>The free list is bounded.  Freeing an object when the list is full will
   * do nothing.
   */
  public final class HessianFreeList<T> {
    private final AtomicReferenceArray<T> _freeStack;
    private final AtomicInteger _top = new AtomicInteger();
  
    /**
     * Create a new free list.
     *
     * @param initialSize maximum number of free objects to store.
     */
    public HessianFreeList(int size)
    {
      _freeStack = new AtomicReferenceArray(size);
    }
    
    /**
     * Try to get an object from the free list.  Returns null if the free list
     * is empty.
     *
     * @return the new object or null.
     */
    public T allocate()
    {
      int top = _top.get();
  
      if (top > 0 && _top.compareAndSet(top, top - 1))
        return _freeStack.getAndSet(top - 1, null);
      else
        return null;
    }
    
    /**
     * Frees the object.  If the free list is full, the object will be garbage
     * collected.
     *
     * @param obj the object to be freed.
     */
    public boolean free(T obj)
    {
      int top = _top.get();
  
      if (top < _freeStack.length()) {
        boolean isFree = _freeStack.compareAndSet(top, null, obj);
        
        _top.compareAndSet(top, top + 1);
  
        return isFree;
      }
      else
        return false;
    }
  
    public boolean allowFree(T obj)
    {
      return _top.get() < _freeStack.length();
    }
  
    /**
     * Frees the object.  If the free list is full, the object will be garbage
     * collected.
     *
     * @param obj the object to be freed.
     */
    public void freeCareful(T obj)
    {
      if (checkDuplicate(obj))
        throw new IllegalStateException("tried to free object twice: " + obj);
  
      free(obj);
    }
  
    /**
     * Debugging to see if the object has already been freed.
     */
    public boolean checkDuplicate(T obj)
    {
      int top = _top.get();
  
      for (int i = top - 1; i >= 0; i--) {
        if (_freeStack.get(i) == obj)
          return true;
      }
  
      return false;
    }
  }
  