| 1 | /* |
| 2 | |
| 3 | Derby - Class org.apache.derby.impl.services.uuid.BasicUUIDFactory |
| 4 | |
| 5 | Copyright 1997, 2004 The Apache Software Foundation or its licensors, as applicable. |
| 6 | |
| 7 | Licensed under the Apache License, Version 2.0 (the "License"); |
| 8 | you may not use this file except in compliance with the License. |
| 9 | You may obtain a copy of the License at |
| 10 | |
| 11 | http://www.apache.org/licenses/LICENSE-2.0 |
| 12 | |
| 13 | Unless required by applicable law or agreed to in writing, software |
| 14 | distributed under the License is distributed on an "AS IS" BASIS, |
| 15 | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 16 | See the License for the specific language governing permissions and |
| 17 | limitations under the License. |
| 18 | |
| 19 | */ |
| 20 | |
| 21 | package org.apache.derby.impl.services.uuid; |
| 22 | |
| 23 | import org.apache.derby.iapi.services.monitor.Monitor; |
| 24 | import org.apache.derby.catalog.UUID; |
| 25 | import org.apache.derby.iapi.services.uuid.UUIDFactory; |
| 26 | |
| 27 | /** |
| 28 | |
| 29 | A hack implementation of something similar to a DCE UUID |
| 30 | generator. Generates unique 128-bit numbers based on the |
| 31 | current machine's internet address, the current time, and |
| 32 | a sequence number. This implementation should be made to |
| 33 | conform to the DCE specification. ("DEC/HP, Network Computing |
| 34 | Architecture, Remote Procedure Call Runtime Extensions |
| 35 | Specification, version OSF TX1.0.11," Steven Miller, July |
| 36 | 23, 1992. This is part of the OSF DCE Documentation. |
| 37 | Chapter 10 describes the UUID generation algorithm.) |
| 38 | <P> |
| 39 | Some known deficiencies: |
| 40 | <ul> |
| 41 | <li> Rather than using the 48-bit hardware network address, |
| 42 | it uses the 32-bit IP address. IP addresses are not |
| 43 | guaranteed to be unique. |
| 44 | <li> There is no provision for generating a suitably unique |
| 45 | number if no IP address is available. |
| 46 | <li> Two processes running on this machine which start their |
| 47 | respective UUID services within a millisecond of one another |
| 48 | may generate duplicate UUIDS. |
| 49 | </ul> |
| 50 | <P> |
| 51 | However, the intention is that UUIDs generated from this class |
| 52 | will be unique with respect to UUIDs generated by other DCE |
| 53 | UUID generators. |
| 54 | |
| 55 | **/ |
| 56 | |
| 57 | public final class BasicUUIDFactory |
| 58 | implements UUIDFactory |
| 59 | { |
| 60 | /* |
| 61 | ** Fields of BasicUUIDFactory. |
| 62 | */ |
| 63 | |
| 64 | private long majorId; // 48 bits only |
| 65 | private long timemillis; |
| 66 | |
| 67 | public BasicUUIDFactory() { |
| 68 | Object env = Monitor.getMonitor().getEnvironment(); |
| 69 | if (env != null) { |
| 70 | String s = env.toString(); |
| 71 | if (s != null) |
| 72 | env = s; |
| 73 | |
| 74 | majorId = ((long) env.hashCode()); |
| 75 | |
| 76 | |
| 77 | } else { |
| 78 | majorId = Runtime.getRuntime().freeMemory(); |
| 79 | } |
| 80 | |
| 81 | majorId &= 0x0000ffffffffffffL; |
| 82 | resetCounters(); |
| 83 | } |
| 84 | |
| 85 | |
| 86 | // |
| 87 | // Constants and fields for computing the sequence number. We started out with monotonically |
| 88 | // increasing sequence numbers but realized that this causes collisions at the |
| 89 | // ends of BTREEs built on UUID columns. So now we have a random number |
| 90 | // generator. We generate these numbers using a technique from Knuth |
| 91 | // "Seminumerical Algorithms," section 3.2 (Generating Uniform Random Numbers). |
| 92 | // The formula is: |
| 93 | // |
| 94 | // next = ( (MULTIPLIER * current) + STEP ) % MODULUS |
| 95 | // |
| 96 | // Here |
| 97 | // |
| 98 | // MODULUS = int size. |
| 99 | // MULTIPLIER = fairly close to the square root of MODULUS to force the |
| 100 | // sequence number to jump around. satisifies the rule that |
| 101 | // (MULTIPLIER-1) is divisible by 4 and by all the primes which |
| 102 | // divide MODULUS. |
| 103 | // STEP = a large number that keeps the sequence number jumping around. |
| 104 | // must be relatively prime to MODULUS. |
| 105 | // INITIAL_VALUE = a number guaranteeing that the first couple sequence numbers |
| 106 | // won't be monotonically increasing. |
| 107 | // |
| 108 | // The sequence numbers should jump around and cycle through all numbers which fit in an int. |
| 109 | |
| 110 | private static final long MODULUS = ( 1L << 32 ); |
| 111 | private static final long MULTIPLIER = ( ( 1L << 14 ) + 1 ); |
| 112 | private static final long STEP = ( ( 1L << 27 ) + 1 ); |
| 113 | private static final long INITIAL_VALUE = ( 2551218188L ); |
| 114 | |
| 115 | private long currentValue; |
| 116 | |
| 117 | /* |
| 118 | ** Methods of UUID |
| 119 | */ |
| 120 | |
| 121 | /** |
| 122 | Generate a new UUID. |
| 123 | @see UUIDFactory#createUUID |
| 124 | **/ |
| 125 | public synchronized UUID createUUID() |
| 126 | { |
| 127 | long cv = currentValue = ( ( MULTIPLIER * currentValue ) + STEP ) % MODULUS; |
| 128 | if ( cv == INITIAL_VALUE ) { bumpMajor(); } |
| 129 | int sequence = (int) cv; |
| 130 | |
| 131 | return new BasicUUID(majorId, timemillis, sequence); |
| 132 | } |
| 133 | |
| 134 | /** |
| 135 | Recreate a UUID previously generated UUID value. |
| 136 | @see UUIDFactory#recreateUUID |
| 137 | **/ |
| 138 | public UUID recreateUUID(String uuidstring) |
| 139 | { |
| 140 | return new BasicUUID(uuidstring); |
| 141 | } |
| 142 | |
| 143 | /** |
| 144 | @see UUIDFactory#recreateUUID |
| 145 | **/ |
| 146 | public UUID recreateUUID(byte[] b) |
| 147 | { |
| 148 | return new BasicUUID(b); |
| 149 | } |
| 150 | |
| 151 | private void bumpMajor() { |
| 152 | |
| 153 | // 48 bits only |
| 154 | majorId = (majorId + 1L) & 0x0000ffffffffffffL; |
| 155 | if (majorId == 0L) |
| 156 | resetCounters(); |
| 157 | |
| 158 | } |
| 159 | private void resetCounters() |
| 160 | { |
| 161 | timemillis = System.currentTimeMillis(); |
| 162 | currentValue = INITIAL_VALUE; |
| 163 | } |
| 164 | } |
| 165 | |