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.api.ldap.model.csn;
021
022
023/**
024 * Generates a new {@link Csn}.
025 * 
026 * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
027 */
028public class CsnFactory
029{
030    /** The last timestamp */
031    private static volatile long lastTimestamp;
032
033    /** The integer used to disambiguate CSN generated at the same time */
034    private int changeCount;
035
036    /** The replicaId to use for every CSN created by this factory */
037    private int replicaId;
038
039    /** A special instance ID for a purge CSN */
040    private static final int PURGE_INSTANCEID = 0x0FFF;
041
042    /** A lock used during the instance creation */
043    private Object lock = new Object();
044
045
046    public CsnFactory( int replicaId )
047    {
048        changeCount = 0;
049        this.replicaId = replicaId;
050    }
051
052
053    /**
054     * Returns a new {@link Csn}.
055     * Generated CSN can be duplicate if user generates CSNs more than 2G 
056     * times a milliseconds.
057     */
058    public Csn newInstance()
059    {
060        int changeCount = 0;
061
062        synchronized ( lock )
063        {
064            long newTimestamp = System.currentTimeMillis();
065
066            // We will be able to generate 2 147 483 647 CSNs each 10 ms max
067            if ( lastTimestamp == newTimestamp )
068            {
069                this.changeCount++;
070            }
071            else
072            {
073                lastTimestamp = newTimestamp;
074                this.changeCount = 0;
075            }
076
077            changeCount = this.changeCount;
078        }
079
080        return new Csn( lastTimestamp, changeCount, replicaId, 0 );
081    }
082
083
084    /**
085     * Returns a new {@link Csn} created from the given values.
086     * 
087     * This method is <b>not</b> to be used except for test purposes.
088     * 
089     * @param timestamp The timestamp to use
090     * @param changeCount The change count to use
091     */
092    public Csn newInstance( long timestamp, int changeCount )
093    {
094        return new Csn( timestamp, changeCount, replicaId, 0 );
095    }
096
097
098    /**
099     * Generates a CSN used to purge data. Its replicaID is not associated
100     * to a server. 
101     * 
102     * @param expirationDate The time up to the first CSN we want to keep 
103     */
104    public Csn newPurgeCsn( long expirationDate )
105    {
106        return new Csn( expirationDate, Integer.MAX_VALUE, PURGE_INSTANCEID, Integer.MAX_VALUE );
107    }
108
109
110    public void setReplicaId( int replicaId )
111    {
112        this.replicaId = replicaId;
113    }
114}