org.cristalise.kernel.utils.SoftCache Maven / Gradle / Ivy

Go to download

Show more of this group Show more artifacts with this name
Show all versions of cristalise-kernel Show documentation

Cristal-ise is a description-driven software platform originally developed to track the construction of the CMS ECAL detector of the LHC at CERN. This is its core library, known as the kernel, which manages business objects called Items. Items are entirely configured from data, called descriptions, held in other Items. Every change of a state in an Item is a consequence of an execution of an activity in that Item's lifecycle, meaning that Cristal-ise applications are completely traceable, even in their design. It also supports extensive versioning of Item description data, giving the system a high level of flexibility.

There is a newer version: 6.0.0

Show newest version

/**
 * This file is part of the CRISTAL-iSE kernel.
 * Copyright (c) 2001-2015 The CRISTAL Consortium. All rights reserved.
 *
 * This library is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published
 * by the Free Software Foundation; either version 3 of the License, or (at
 * your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; with out even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this library; if not, write to the Free Software Foundation,
 * Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
 *
 * http://www.fsf.org/licensing/licenses/lgpl.html
 */
package org.cristalise.kernel.utils;

import java.lang.ref.ReferenceQueue;
import java.lang.ref.SoftReference;
import java.util.AbstractMap;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.Map;
import java.util.Set;

/*******************************************************************************
 * SoftReferences are reaped if no strong references are left and the vm is
 * running out of memory. Most caches in the kernel use this.
 *
 * $Revision: 1.5 $ $Date: 2004/10/29 13:29:09 $
 ******************************************************************************/
public class SoftCache extends AbstractMap {

    private final Map> hash = new HashMap>();
    private final int minSize;
    private final LinkedList hardCache = new LinkedList();
    private final ReferenceQueue queue = new ReferenceQueue();

    public SoftCache() {
        this(0);
    }

    public SoftCache(int minSize) {
        this.minSize = minSize;
    }

    @Override
    public V get(Object key) {
        V result = null;
        SoftValue soft_ref = hash.get(key);
        if (soft_ref != null) {
            result = soft_ref.get();
            if (result == null)
                hash.remove(key);
            else
                if (minSize > 0) { // add to hard cache so it's not reaped for a while
                	synchronized(hardCache) {
                		hardCache.addFirst(result);
                		if (hardCache.size() > minSize) // trim last one off
                			hardCache.removeLast();
                	}
                }
        }
        return result;
    }

    @Override
	public V put(K key, V value) {
        processQueue();
        if (minSize > 0) {
        	synchronized(hardCache) {
        		hardCache.addFirst(value);
        		if (hardCache.size() > minSize)
        			hardCache.removeLast();
        	}
        }
        hash.put(key, new SoftValue(key, value, queue));
        return value;
    }

    @Override
	public V remove(Object key) {
        processQueue();
        if (hash.containsKey(key)) return hash.remove(key).get();
        return null;
    }

    @Override
	public void clear() {
    	synchronized(hardCache) {
    		hardCache.clear();
    	}
        while(queue.poll()!=null);
        hash.clear();
    }

    @Override
	public int size() {
        processQueue();
        return hash.size();
    }

    @Override
	public Set keySet() {
        processQueue();
        return hash.keySet();
    }

    @Override
	public Set> entrySet() {
        // Would have to create another Map to do this - too expensive
        // Throwing runtime expensive is dangerous, but better than nulls
        throw new UnsupportedOperationException();
    }

    private static class SoftValue extends SoftReference {
        private final Object key;
        private SoftValue(Object key, V value, ReferenceQueue q) {
            super(value, q);
            this.key = key;
        }
    }

    /**
     * Look for values that have been reaped, and remove their keys from the cache
     */
    private void processQueue() {
        SoftValue sv;
        while ((sv = (SoftValue) queue.poll()) != null) {
            hash.remove(sv.key);
        }
    }

}