trunk/ldap/model/src/main/java/org/apache/directory/api/ldap/model/csn/CsnFactory.java

/*
 *  Licensed to the Apache Software Foundation (ASF) under one
 *  or more contributor license agreements.  See the NOTICE file
 *  distributed with this work for additional information
 *  regarding copyright ownership.  The ASF licenses this file
 *  to you under the Apache License, Version 2.0 (the
 *  "License"); you may not use this file except in compliance
 *  with the License.  You may obtain a copy of the License at
 *  
 *    http://www.apache.org/licenses/LICENSE-2.0
 *  
 *  Unless required by applicable law or agreed to in writing,
 *  software distributed under the License is distributed on an
 *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 *  KIND, either express or implied.  See the License for the
 *  specific language governing permissions and limitations
 *  under the License. 
 *  
 */
package org.apache.directory.api.ldap.model.csn;


/**
 * Generates a new {@link Csn}.
 * 
 * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
 */
public class CsnFactory
{
    /** The last timestamp */
    private static volatile long lastTimestamp;

    /** The integer used to disambiguate CSN generated at the same time */
    private int changeCount;

    /** The replicaId to use for every CSN created by this factory */
    private int replicaId;

    /** A special instance ID for a purge CSN */
    private static final int PURGE_INSTANCEID = 0x0FFF;

    /** A lock used during the instance creation */
    private Object lock = new Object();


    public CsnFactory( int replicaId )
    {
        changeCount = 0;
        this.replicaId = replicaId;
    }


    /**
     * Returns a new {@link Csn}.
     * Generated CSN can be duplicate if user generates CSNs more than 2G 
     * times a milliseconds.
     */
    public Csn newInstance()
    {
        int tmpChangeCount = 0;

        synchronized ( lock )
        {
            long newTimestamp = System.currentTimeMillis();

            // We will be able to generate 2 147 483 647 CSNs each 10 ms max
            if ( lastTimestamp == newTimestamp )
            {
                changeCount++;
            }
            else
            {
                lastTimestamp = newTimestamp;
                changeCount = 0;
            }

            tmpChangeCount = changeCount;
        }

        return new Csn( lastTimestamp, tmpChangeCount, replicaId, 0 );
    }


    /**
     * Returns a new {@link Csn} created from the given values.
     * 
     * This method is <b>not</b> to be used except for test purposes.
     * 
     * @param timestamp The timestamp to use
     * @param changeCount The change count to use
     */
    public Csn newInstance( long timestamp, int changeCount )
    {
        return new Csn( timestamp, changeCount, replicaId, 0 );
    }


    /**
     * Generates a CSN used to purge data. Its replicaID is not associated
     * to a server. 
     * 
     * @param expirationDate The time up to the first CSN we want to keep 
     */
    public Csn newPurgeCsn( long expirationDate )
    {
        return new Csn( expirationDate, Integer.MAX_VALUE, PURGE_INSTANCEID, Integer.MAX_VALUE );
    }


    public void setReplicaId( int replicaId )
    {
        this.replicaId = replicaId;
    }
}