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 */
020 package org.apache.directory.shared.ldap.csn;
021
022 import java.util.concurrent.atomic.AtomicInteger;
023
024
025 /**
026 * Generates a new {@link Csn}.
027 *
028 * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
029 */
030 public class CsnFactory
031 {
032 /** The last timestamp */
033 private static volatile long lastTimestamp;
034
035 /** The integer used to disambiguate CSN generated at the same time */
036 private AtomicInteger changeCount;
037
038 /** The replicaId to use for every CSN created by this factory */
039 private int replicaId;
040
041 /** A special instance ID for a purge CSN */
042 private static final int PURGE_INSTANCEID = 0x0FFF;
043
044
045 public CsnFactory( int replicaId )
046 {
047 changeCount = new AtomicInteger( 0 );
048 this.replicaId = replicaId;
049 }
050
051
052 /**
053 * Returns a new {@link Csn}.
054 * Generated CSN can be duplicate if user generates CSNs more than 2G
055 * times a milliseconds.
056 */
057 public Csn newInstance()
058 {
059 synchronized ( changeCount )
060 {
061 long newTimestamp = System.currentTimeMillis();
062
063 // We will be able to generate 2 147 483 647 CSNs each 10 ms max
064 if ( lastTimestamp == newTimestamp )
065 {
066 changeCount.incrementAndGet();
067 }
068 else
069 {
070 lastTimestamp = newTimestamp;
071 changeCount.set( 0 );
072 }
073 }
074
075 return new Csn( lastTimestamp, changeCount.get(), replicaId, 0 );
076 }
077
078
079 /**
080 * Returns a new {@link Csn} created from the given values.
081 *
082 * This method is <b>not</b> to be used except for test purposes.
083 *
084 * @param timestamp The timestamp to use
085 * @param replicaId Replica ID. ReplicaID must be 1-3 digit value
086 * @param changeCount The change count to use
087 */
088 public Csn newInstance( long timestamp, int changeCount )
089 {
090 return new Csn( timestamp, changeCount, replicaId, 0 );
091 }
092
093
094 /**
095 * Generates a CSN used to purge data. Its replicaID is not associated
096 * to a server.
097 *
098 * @param expirationDate The time up to the first CSN we want to keep
099 */
100 public Csn newPurgeCsn( long expirationDate )
101 {
102 return new Csn( expirationDate, Integer.MAX_VALUE, PURGE_INSTANCEID, Integer.MAX_VALUE );
103 }
104 }