org.neo4j.kernel.impl.cache.LruCache Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of neo4j-kernel Show documentation
Neo4j kernel is a lightweight, embedded Java database designed to store data structured as graphs rather than tables. For more information, see http://neo4j.org.
There is a newer version: 5.26.0
Show newest version
/*
 * Copyright (c) 2002-2015 "Neo Technology,"
 * Network Engine for Objects in Lund AB [http://neotechnology.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j is free software: you can redistribute it and/or modify
 * it under the terms of the GNU 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see .
 */
package org.neo4j.kernel.impl.cache;

import java.util.Collection;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Set;

/**
 * Simple implementation of Least-recently-used cache.
 * 
 * The cache has a maxSize set and when the number of cached
 * elements exceeds that limit the least recently used element will be removed.
 */
public class LruCache
{
    private final String name;
    private int maxSize;

    private final Map cache = new LinkedHashMap( 500, 0.75f, true )
    {
        @Override
        protected boolean removeEldestEntry( Map.Entry eldest )
        {
            // synchronization miss with old value on maxSize here is ok
            if ( size() > maxSize )
            {
                elementCleaned( eldest.getValue() );
                return true;
            }
            return false;
        }
    };

    /**
     * Creates a LRU cache. If maxSize < 1 an
     * IllegalArgumentException is thrown.
     *
     * @param name    name of cache
     * @param maxSize maximum size of this cache
     */
    public LruCache( String name, int maxSize )
    {
        if ( name == null || maxSize < 1 )
        {
            throw new IllegalArgumentException( "maxSize=" + maxSize + ", name=" + name );
        }
        this.name = name;
        this.maxSize = maxSize;
    }

    public String getName()
    {
        return this.name;
    }

    /**
     * Returns the maximum size of this cache.
     *
     * @return maximum size
     */
    public int maxSize()
    {
        return maxSize;
    }

    public synchronized void put( K key, E element )
    {
        if ( key == null || element == null )
        {
            throw new IllegalArgumentException( "key=" + key + ", element=" + element );
        }
        cache.put( key, element );
    }

    public synchronized E remove( K key )
    {
        if ( key == null )
        {
            throw new IllegalArgumentException( "Null parameter" );
        }
        return cache.remove( key );
    }

    public synchronized E get( K key )
    {
        if ( key == null )
        {
            throw new IllegalArgumentException();
        }
        return counter.count( cache.get( key ) );
    }

    public synchronized void clear()
    {
        for ( Map.Entry keEntry : cache.entrySet() )
        {
            elementCleaned( keEntry.getValue() );
        }
        cache.clear();
    }

    public synchronized int size()
    {
        return cache.size();
    }

    public synchronized Set keySet()
    {
        return cache.keySet();
    }

    public synchronized Collection values()
    {
        return cache.values();
    }

    public synchronized Set> entrySet()
    {
        return cache.entrySet();
    }

    public synchronized void putAll( Map map )
    {
        cache.putAll( map );
    }

    /**
     * Changes the max size of the cache. If newMaxSize is
     * greater then maxSize() next invoke to maxSize()
     * will return newMaxSize and the entries in cache will not
     * be modified.
     * 

     * If newMaxSize is less then size()
     * the cache will shrink itself removing least recently used element until
     * size() equals newMaxSize. For each element
     * removed the {@link #elementCleaned} method is invoked.
     * 
     * If newMaxSize is less then 1 an
     * {@link IllegalArgumentException} is thrown.
     *
     * @param newMaxSize the new maximum size of the cache
     */
    public synchronized void resize( int newMaxSize )
    {
        if ( newMaxSize < 1 )
        {
            throw new IllegalArgumentException( "newMaxSize=" + newMaxSize );
        }

        if ( newMaxSize >= size() )
        {
            maxSize = newMaxSize;
        }
        else
        {
            maxSize = newMaxSize;
            java.util.Iterator> itr = cache.entrySet().iterator();
            while ( itr.hasNext() && cache.size() > maxSize )
            {
                E element = itr.next().getValue();
                itr.remove();
                elementCleaned( element );
            }
        }
    }

    public void elementCleaned( E element )
    {
    }

    private final HitCounter counter = new HitCounter();

    public long hitCount()
    {
        return counter.getHitsCount();
    }

    public long missCount()
    {
        return counter.getMissCount();
    }
}