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 }