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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.

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/**
 * 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.Reference;
import java.util.AbstractMap;
import java.util.AbstractSet;
import java.util.Hashtable;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
/**************************************************************************
 * TransientCache - Uses transient references to allow unused entries to be
 * reaped by the java garbage collector.
 *
 * $Revision: 1.1 $
 * $Date: 2004/04/20 09:37:02 $
 *
 * Copyright (C) 2003 CERN - European Organization for Nuclear Research
 * All rights reserved.
 **************************************************************************/
public abstract class TransientCache extends AbstractMap {

    private Map> map = new Hashtable>();

    @Override
	public synchronized Set> entrySet() {
        Map newMap = new Hashtable();
        Iterator>> iter = map.entrySet().iterator();
        while (iter.hasNext()) {
        	Entry> me = iter.next();
            Reference ref = me.getValue();
            V o = ref.get();
            if (o == null) {
                // Delete cleared reference
                iter.remove();
            } else {
                // Copy out interior object
                newMap.put(me.getKey(), o);
            }
        }
        // Return set of interior objects
        return newMap.entrySet();
    }

    @Override
	public synchronized V put(K key, V value) {
        Reference ref = makeReference(value);
        ref = map.put(key, ref);
        if (ref != null)
            return (ref.get());
        return null;
    }

    public abstract Reference makeReference(Object value);

    @Override
	public V remove(Object key) {
        Iterator>> i = map.entrySet().iterator();
        Entry> correctEntry = null;
        if (key == null) {
            while (correctEntry == null && i.hasNext()) {
                Entry> e = i.next();
                if (e.getKey() == null)
                    correctEntry = e;
            }
        } else {
            while (correctEntry == null && i.hasNext()) {
            	Entry> e = i.next();
                if (key.equals(e.getKey()))
                    correctEntry = e;
            }
        }
        V oldValue = null;
        if (correctEntry != null) {
            Reference correctReference = correctEntry.getValue();
            oldValue = correctReference.get();
            i.remove();
        }
        return oldValue;
    }
    /**
     *
     */
    @Override
	public void clear() {
        map.entrySet().clear();
    }

    private transient Set keySet = null;

    @Override
	public Set keySet() {
        if (keySet == null) {
            keySet = new AbstractSet() {
            @Override
			public Iterator iterator() {
                return new Iterator() {
                private Iterator>> i = map.entrySet().iterator();

                @Override
				public boolean hasNext() {
                    return i.hasNext();
                }

                @Override
				public K next() {
                    return i.next().getKey();
                }

                @Override
				public void remove() {
                    i.remove();
                }
                        };
            }

            @Override
			public int size() {
                return TransientCache.this.size();
            }

            @Override
			public boolean contains(Object k) {
                return TransientCache.this.containsKey(k);
            }
            };
        }
        return keySet;
        }

}