001 //$HeadURL: svn+ssh://rbezema@svn.wald.intevation.org/deegree/base/tags/2.1/src/org/deegree/framework/util/BasicUUIDFactory.java $
002 /*
003 *
004 This class orginaly has been part of the apache derby project. It has
005 slightly been changed to match the requirements of deegree.
006
007 Derby - Class org.apache.derby.impl.services.uuid.BasicUUIDFactory
008
009 Copyright 1997, 2004 The Apache Software Foundation or its licensors, as applicable.
010
011 Licensed under the Apache License, Version 2.0 (the "License");
012 you may not use this file except in compliance with the License.
013 You may obtain a copy of the License at
014
015 http://www.apache.org/licenses/LICENSE-2.0
016
017 Unless required by applicable law or agreed to in writing, software
018 distributed under the License is distributed on an "AS IS" BASIS,
019 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
020 See the License for the specific language governing permissions and
021 limitations under the License.
022
023 */
024
025 package org.deegree.framework.util;
026
027 /**
028 *
029 * A hack implementation of something similar to a DCE UUID generator. Generates unique 128-bit
030 * numbers based on the current machine's internet address, the current time, and a sequence number.
031 * This implementation should be made to conform to the DCE specification. ("DEC/HP, Network
032 * Computing Architecture, Remote Procedure Call Runtime Extensions Specification, version OSF
033 * TX1.0.11," Steven Miller, July 23, 1992. This is part of the OSF DCE Documentation. Chapter 10
034 * describes the UUID generation algorithm.)
035 * <P>
036 * Some known deficiencies:
037 * <ul>
038 * <li> Rather than using the 48-bit hardware network address, it uses the 32-bit IP address. IP
039 * addresses are not guaranteed to be unique.
040 * <li> There is no provision for generating a suitably unique number if no IP address is available.
041 * <li> Two processes running on this machine which start their respective UUID services within a
042 * millisecond of one another may generate duplicate UUIDS.
043 * </ul>
044 * <P>
045 * However, the intention is that UUIDs generated from this class will be unique with respect to
046 * UUIDs generated by other DCE UUID generators.
047 *
048 * @deprecated use
049 * @see UUID
050 *
051 */
052
053 public final class BasicUUIDFactory {
054 /*
055 * * Fields of BasicUUIDFactory.
056 */
057
058 private long majorId; // 48 bits only
059
060 private long timemillis;
061
062 public BasicUUIDFactory() {
063
064 majorId = Runtime.getRuntime().freeMemory();
065
066 majorId &= 0x0000ffffffffffffL;
067 resetCounters();
068 }
069
070 public BasicUUIDFactory( long majorId ) {
071
072 this.majorId = majorId;
073
074 this.majorId &= 0x0000ffffffffffffL;
075 resetCounters();
076 }
077
078 //
079 // Constants and fields for computing the sequence number. We started out with monotonically
080 // increasing sequence numbers but realized that this causes collisions at the
081 // ends of BTREEs built on UUID columns. So now we have a random number
082 // generator. We generate these numbers using a technique from Knuth
083 // "Seminumerical Algorithms," section 3.2 (Generating Uniform Random Numbers).
084 // The formula is:
085 //
086 // next = ( (MULTIPLIER * current) + STEP ) % MODULUS
087 //
088 // Here
089 //
090 // MODULUS = int size.
091 // MULTIPLIER = fairly close to the square root of MODULUS to force the
092 // sequence number to jump around. satisifies the rule that
093 // (MULTIPLIER-1) is divisible by 4 and by all the primes which
094 // divide MODULUS.
095 // STEP = a large number that keeps the sequence number jumping around.
096 // must be relatively prime to MODULUS.
097 // INITIAL_VALUE = a number guaranteeing that the first couple sequence numbers
098 // won't be monotonically increasing.
099 //
100 // The sequence numbers should jump around and cycle through all numbers which fit in an int.
101
102 private static final long MODULUS = ( 1L << 32 );
103
104 private static final long MULTIPLIER = ( ( 1L << 14 ) + 1 );
105
106 private static final long STEP = ( ( 1L << 27 ) + 1 );
107
108 private static final long INITIAL_VALUE = ( 2551218188L );
109
110 private long currentValue;
111
112 /*
113 * * Methods of UUID
114 */
115
116 /**
117 * Generate a new UUID.
118 *
119 * @see UUIDFactory#createUUID
120 */
121 public synchronized UUID createUUID() {
122 long cv = currentValue = ( ( MULTIPLIER * currentValue ) + STEP ) % MODULUS;
123 if ( cv == INITIAL_VALUE ) {
124 bumpMajor();
125 }
126 int sequence = (int) cv;
127
128 return new BasicUUID( majorId, timemillis, sequence );
129 }
130
131 /**
132 * Recreate a UUID previously generated UUID value.
133 *
134 * @see UUIDFactory#recreateUUID
135 */
136 public UUID recreateUUID( String uuidstring ) {
137 return new BasicUUID( uuidstring );
138 }
139
140 /**
141 * @see UUIDFactory#recreateUUID
142 */
143 public UUID recreateUUID( byte[] b ) {
144 return new BasicUUID( b );
145 }
146
147 private void bumpMajor() {
148
149 // 48 bits only
150 majorId = ( majorId + 1L ) & 0x0000ffffffffffffL;
151 if ( majorId == 0L )
152 resetCounters();
153
154 }
155
156 private void resetCounters() {
157 timemillis = System.currentTimeMillis();
158 currentValue = INITIAL_VALUE;
159 }
160 }