001/*
002 *  Licensed to the Apache Software Foundation (ASF) under one
003 *  or more contributor license agreements.  See the NOTICE file
004 *  distributed with this work for additional information
005 *  regarding copyright ownership.  The ASF licenses this file
006 *  to you under the Apache License, Version 2.0 (the
007 *  "License"); you may not use this file except in compliance
008 *  with the License.  You may obtain a copy of the License at
009 *  
010 *    http://www.apache.org/licenses/LICENSE-2.0
011 *  
012 *  Unless required by applicable law or agreed to in writing,
013 *  software distributed under the License is distributed on an
014 *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015 *  KIND, either express or implied.  See the License for the
016 *  specific language governing permissions and limitations
017 *  under the License. 
018 *  
019 */
020package org.apache.directory.server.core.api.subtree;
021
022
023import java.util.Iterator;
024import java.util.Map;
025import java.util.concurrent.ConcurrentHashMap;
026import java.util.concurrent.atomic.AtomicInteger;
027
028import org.apache.directory.api.ldap.model.name.Dn;
029import org.apache.directory.api.ldap.model.subtree.Subentry;
030
031
032/**
033 * A cache for subtree specifications. It associates a Subentry with a Dn,
034 * representing its position in the DIT.<br>
035 * This cache has a size limit set to 1000 at the moment. We should add a configuration
036 * parameter to manage its size.
037 *
038 * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
039 */
040public class SubentryCache implements Iterable<Dn>
041{
042    /** The default cache size limit */
043    private static final int DEFAULT_CACHE_MAX_SIZE = 1000;
044
045    /** The cache size limit */
046    private int cacheMaxSize = DEFAULT_CACHE_MAX_SIZE;
047
048    /** The current cache size */
049    private AtomicInteger cacheSize;
050
051    /** The Subentry cache */
052    private final Map<Dn, Subentry> cache;
053
054
055    /**
056     * Creates a new instance of SubentryCache with a default maximum size.
057     */
058    public SubentryCache()
059    {
060        cache = new ConcurrentHashMap<>();
061        cacheSize = new AtomicInteger( 0 );
062    }
063
064
065    /**
066     * Creates a new instance of SubentryCache with a specific maximum size.
067     * 
068     * @param maxSize The max number of elements in teh cache
069     */
070    public SubentryCache( int maxSize )
071    {
072        cache = new ConcurrentHashMap<>();
073        cacheSize = new AtomicInteger( 0 );
074        cacheMaxSize = maxSize;
075    }
076
077
078    /**
079     * Retrieve a Subentry given a Dn. If there is none, null will be returned.
080     *
081     * @param dn The Dn we want to get the Subentry for
082     * @return The found Subentry, or null
083     */
084    public final Subentry getSubentry( Dn dn )
085    {
086        return cache.get( dn );
087    }
088
089
090    /**
091     * Remove a Subentry for a given Dn
092     *
093     * @param dn The Dn for which we want to remove the
094     * associated Subentry
095     * @return The removed Subentry, if any
096     */
097    public final Subentry removeSubentry( Dn dn )
098    {
099        Subentry oldSubentry = cache.remove( dn );
100
101        if ( oldSubentry != null )
102        {
103            cacheSize.decrementAndGet();
104        }
105
106        return oldSubentry;
107    }
108
109
110    /**
111     * Stores a new Subentry into the cache, associated with a Dn
112     *
113     * @param dn The Subentry Dn
114     * @param subentry The SubtreeSpecification
115     * @return The old Subentry, if any
116     */
117    public Subentry addSubentry( Dn dn, Subentry subentry )
118    {
119        if ( cacheSize.get() > cacheMaxSize )
120        {
121            throw new IllegalStateException( "Cache is full: size=" + cacheSize.get() + ", max=" + cacheMaxSize );
122        }
123
124        Subentry oldSubentry = cache.put( dn, subentry );
125
126        if ( oldSubentry == null )
127        {
128            cacheSize.getAndIncrement();
129        }
130
131        return oldSubentry;
132    }
133
134
135    /**
136     * Tells if there is a Subentry associated with a Dn
137     * @param dn The Dn
138     * @return True if a Subentry is found
139     */
140    public boolean hasSubentry( Dn dn )
141    {
142        return cache.containsKey( dn );
143    }
144
145
146    /**
147     * @return An Iterator over the Subentry's DNs 
148     */
149    public Iterator<Dn> iterator()
150    {
151        return cache.keySet().iterator();
152    }
153
154
155    /**
156     * @return The number of elements in the cache
157     */
158    public int getCacheSize()
159    {
160        return cacheSize.get();
161    }
162}