cachelru.java

实现数据库的storage manager 功能

/*
 * Copyright (c) 2000-2004, Rickard C鰏ter, Martin Svensson
 * 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 SICS 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 com.mellowtech.disc;

import java.util.*;

/**
 * Simple cache that use the least resently used scheme. When the cache limit
 * is reached and an item has to be unloaded the cache chooses the item that
 * was accessed longest ago.
 * put, get, and remove all work in log(n) time.
 */
public class CacheLRU extends AbstractCache{

  LRUCache lru = null;

  public CacheLRU(CacheCallback callback, int newSize){
    setCallback(callback);
    setSize(newSize);
  }

  public void clearCache(){
    lru.clear();
  }

  public void dirty(Object key, Object value){
    CacheValue cv = (CacheValue) lru.get(key);
    if(cv == null){
      put(key, value);
      cv = (CacheValue) lru.get(key);
    }
    cv.setDirty();
  }

  public void notDirty(Object key){
    CacheValue cv = (CacheValue) lru.get(key);
    if(cv == null)
      return;
    
    cv.setDirty(false);
  }

  public Object get(Object key){
    CacheValue cv = (CacheValue) lru.get(key);
    return (cv != null) ? cv.getValue() : null;
  }

  public Iterator iterator(){
    return lru.entrySet().iterator();
  }

  public void put(Object key, Object value){
    if(!lru.containsKey(key))
      lru.put(key, new CacheValue(value));
  }

  public void remove(Object key){
    CacheValue cv = (CacheValue) lru.get(key);
    if(cv == null)
      return;
    if(cv.isDirty() && callback != null)
      callback.remove(key, cv.getValue());
  }

  public void setSize(int size){
    maxSize = size;
    if(lru != null){
      Map.Entry entry;
      for(Iterator it = iterator(); it.hasNext();){
	entry = (Map.Entry) it.next();
	callback.remove(entry.getKey(), entry.getValue());
      }
    }
    lru = new LRUCache(size, 1.0f, true);
  }


  
  class LRUCache extends LinkedHashMap{

    public LRUCache(int size, float load, boolean order){
      super(size, load, order);
    }
    
    protected boolean removeEldestEntry(Map.Entry eldest) {
      if(size() > maxSize){
	callback.remove(eldest.getKey(), ((CacheValue)eldest.getValue()).getValue());
	return true;
      }
      return false;
    }
  
  }
  
					   
  
}