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| 1 | /* | ||
| 2 | * Copyright (c) 1996, 2006, Oracle and/or its affiliates. All rights reserved. | ||
| 3 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. | ||
| 4 | * | ||
| 5 | * This code is free software; you can redistribute it and/or modify it | ||
| 6 | * under the terms of the GNU General Public License version 2 only, as | ||
| 7 | * published by the Free Software Foundation. Oracle designates this | ||
| 8 | * particular file as subject to the "Classpath" exception as provided | ||
| 9 | * by Oracle in the LICENSE file that accompanied this code. | ||
| 10 | * | ||
| 11 | * This code is distributed in the hope that it will be useful, but WITHOUT | ||
| 12 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | ||
| 13 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | ||
| 14 | * version 2 for more details (a copy is included in the LICENSE file that | ||
| 15 | * accompanied this code). | ||
| 16 | * | ||
| 17 | * You should have received a copy of the GNU General Public License version | ||
| 18 | * 2 along with this work; if not, write to the Free Software Foundation, | ||
| 19 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | ||
| 20 | * | ||
| 21 | * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | ||
| 22 | * or visit www.oracle.com if you need additional information or have any | ||
| 23 | * questions. | ||
| 24 | */ | ||
| 25 | package java.rmi.server; | ||
| 26 | |||
| 27 | import java.io.DataInput; | ||
| 28 | import java.io.DataOutput; | ||
| 29 | import java.io.IOException; | ||
| 30 | import java.io.Serializable; | ||
| 31 | import java.security.SecureRandom; | ||
| 32 | |||
| 33 | /** | ||
| 34 | * A <code>UID</code> represents an identifier that is unique over time | ||
| 35 | * with respect to the host it is generated on, or one of 2<sup>16</sup> | ||
| 36 | * "well-known" identifiers. | ||
| 37 | * | ||
| 38 | * <p>The {@link #UID()} constructor can be used to generate an | ||
| 39 | * identifier that is unique over time with respect to the host it is | ||
| 40 | * generated on. The {@link #UID(short)} constructor can be used to | ||
| 41 | * create one of 2<sup>16</sup> well-known identifiers. | ||
| 42 | * | ||
| 43 | * <p>A <code>UID</code> instance contains three primitive values: | ||
| 44 | * <ul> | ||
| 45 | * <li><code>unique</code>, an <code>int</code> that uniquely identifies | ||
| 46 | * the VM that this <code>UID</code> was generated in, with respect to its | ||
| 47 | * host and at the time represented by the <code>time</code> value (an | ||
| 48 | * example implementation of the <code>unique</code> value would be a | ||
| 49 | * process identifier), | ||
| 50 | * or zero for a well-known <code>UID</code> | ||
| 51 | * <li><code>time</code>, a <code>long</code> equal to a time (as returned | ||
| 52 | * by {@link System#currentTimeMillis()}) at which the VM that this | ||
| 53 | * <code>UID</code> was generated in was alive, | ||
| 54 | * or zero for a well-known <code>UID</code> | ||
| 55 | * <li><code>count</code>, a <code>short</code> to distinguish | ||
| 56 | * <code>UID</code>s generated in the same VM with the same | ||
| 57 | * <code>time</code> value | ||
| 58 | * </ul> | ||
| 59 | * | ||
| 60 | * <p>An independently generated <code>UID</code> instance is unique | ||
| 61 | * over time with respect to the host it is generated on as long as | ||
| 62 | * the host requires more than one millisecond to reboot and its system | ||
| 63 | * clock is never set backward. A globally unique identifier can be | ||
| 64 | * constructed by pairing a <code>UID</code> instance with a unique host | ||
| 65 | * identifier, such as an IP address. | ||
| 66 | * | ||
| 67 | * @author Ann Wollrath | ||
| 68 | * @author Peter Jones | ||
| 69 | * @since JDK1.1 | ||
| 70 | */ | ||
| 71 | public final class UID implements Serializable { | ||
| 72 | |||
| 73 | private static int hostUnique; | ||
| 74 | private static boolean hostUniqueSet = false; | ||
| 75 | |||
| 76 | private static final Object lock = new Object(); | ||
| 77 | private static long lastTime = System.currentTimeMillis(); | ||
| 78 | private static short lastCount = Short.MIN_VALUE; | ||
| 79 | |||
| 80 | /** indicate compatibility with JDK 1.1.x version of class */ | ||
| 81 | private static final long serialVersionUID = 1086053664494604050L; | ||
| 82 | |||
| 83 | /** | ||
| 84 | * number that uniquely identifies the VM that this <code>UID</code> | ||
| 85 | * was generated in with respect to its host and at the given time | ||
| 86 | * @serial | ||
| 87 | */ | ||
| 88 | private final int unique; | ||
| 89 | |||
| 90 | /** | ||
| 91 | * a time (as returned by {@link System#currentTimeMillis()}) at which | ||
| 92 | * the VM that this <code>UID</code> was generated in was alive | ||
| 93 | * @serial | ||
| 94 | */ | ||
| 95 | private final long time; | ||
| 96 | |||
| 97 | /** | ||
| 98 | * 16-bit number to distinguish <code>UID</code> instances created | ||
| 99 | * in the same VM with the same time value | ||
| 100 | * @serial | ||
| 101 | */ | ||
| 102 | private final short count; | ||
| 103 | |||
| 104 | /** | ||
| 105 | * Generates a <code>UID</code> that is unique over time with | ||
| 106 | * respect to the host that it was generated on. | ||
| 107 | */ | ||
| 108 | public UID() { | ||
| 109 | |||
| 110 | synchronized (lock) { | ||
| 111 | if (!hostUniqueSet) { | ||
| 112 | hostUnique = (new SecureRandom()).nextInt(); | ||
| 113 | hostUniqueSet = true; | ||
| 114 | } | ||
| 115 | unique = hostUnique; | ||
| 116 | if (lastCount == Short.MAX_VALUE) { | ||
| 117 | boolean interrupted = Thread.interrupted(); | ||
| 118 | boolean done = false; | ||
| 119 | while (!done) { | ||
| 120 | long now = System.currentTimeMillis(); | ||
| 121 | if (now <= lastTime) { | ||
| 122 | // wait for time to change | ||
| 123 | try { | ||
| 124 | Thread.currentThread().sleep(1); | ||
| 125 | } catch (InterruptedException e) { | ||
| 126 | interrupted = true; | ||
| 127 | } | ||
| 128 | } else { | ||
| 129 | lastTime = now; | ||
| 130 | lastCount = Short.MIN_VALUE; | ||
| 131 | done = true; | ||
| 132 | } | ||
| 133 | } | ||
| 134 | if (interrupted) { | ||
| 135 | Thread.currentThread().interrupt(); | ||
| 136 | } | ||
| 137 | } | ||
| 138 | time = lastTime; | ||
| 139 | count = lastCount++; | ||
| 140 | } | ||
| 141 | } | ||
| 142 | |||
| 143 | /** | ||
| 144 | * Creates a "well-known" <code>UID</code>. | ||
| 145 | * | ||
| 146 | * There are 2<sup>16</sup> possible such well-known ids. | ||
| 147 | * | ||
| 148 | * <p>A <code>UID</code> created via this constructor will not | ||
| 149 | * clash with any <code>UID</code>s generated via the no-arg | ||
| 150 | * constructor. | ||
| 151 | * | ||
| 152 | * @param num number for well-known <code>UID</code> | ||
| 153 | */ | ||
| 154 | public UID(short num) { | ||
| 155 | unique = 0; | ||
| 156 | time = 0; | ||
| 157 | count = num; | ||
| 158 | } | ||
| 159 | |||
| 160 | /** | ||
| 161 | * Constructs a <code>UID</code> given data read from a stream. | ||
| 162 | */ | ||
| 163 | private UID(int unique, long time, short count) { | ||
| 164 | this.unique = unique; | ||
| 165 | this.time = time; | ||
| 166 | this.count = count; | ||
| 167 | } | ||
| 168 | |||
| 169 | /** | ||
| 170 | * Returns the hash code value for this <code>UID</code>. | ||
| 171 | * | ||
| 172 | * @return the hash code value for this <code>UID</code> | ||
| 173 | */ | ||
| 174 | public int hashCode() { | ||
| 175 | return (int) time + (int) count; | ||
| 176 | } | ||
| 177 | |||
| 178 | /** | ||
| 179 | * Compares the specified object with this <code>UID</code> for | ||
| 180 | * equality. | ||
| 181 | * | ||
| 182 | * This method returns <code>true</code> if and only if the | ||
| 183 | * specified object is a <code>UID</code> instance with the same | ||
| 184 | * <code>unique</code>, <code>time</code>, and <code>count</code> | ||
| 185 | * values as this one. | ||
| 186 | * | ||
| 187 | * @param obj the object to compare this <code>UID</code> to | ||
| 188 | * | ||
| 189 | * @return <code>true</code> if the given object is equivalent to | ||
| 190 | * this one, and <code>false</code> otherwise | ||
| 191 | */ | ||
| 192 | public boolean equals(Object obj) { | ||
| 193 | if (obj instanceof UID) { | ||
| 194 | UID uid = (UID) obj; | ||
| 195 | return (unique == uid.unique && | ||
| 196 | count == uid.count && | ||
| 197 | time == uid.time); | ||
| 198 | } else { | ||
| 199 | return false; | ||
| 200 | } | ||
| 201 | } | ||
| 202 | |||
| 203 | /** | ||
| 204 | * Returns a string representation of this <code>UID</code>. | ||
| 205 | * | ||
| 206 | * @return a string representation of this <code>UID</code> | ||
| 207 | */ | ||
| 208 | public String toString() { | ||
| 209 | return Integer.toString(unique,16) + ":" + | ||
| 210 | Long.toString(time,16) + ":" + | ||
| 211 | Integer.toString(count,16); | ||
| 212 | } | ||
| 213 | |||
| 214 | /** | ||
| 215 | * Marshals a binary representation of this <code>UID</code> to | ||
| 216 | * a <code>DataOutput</code> instance. | ||
| 217 | * | ||
| 218 | * <p>Specifically, this method first invokes the given stream's | ||
| 219 | * {@link DataOutput#writeInt(int)} method with this <code>UID</code>'s | ||
| 220 | * <code>unique</code> value, then it invokes the stream's | ||
| 221 | * {@link DataOutput#writeLong(long)} method with this <code>UID</code>'s | ||
| 222 | * <code>time</code> value, and then it invokes the stream's | ||
| 223 | * {@link DataOutput#writeShort(int)} method with this <code>UID</code>'s | ||
| 224 | * <code>count</code> value. | ||
| 225 | * | ||
| 226 | * @param out the <code>DataOutput</code> instance to write | ||
| 227 | * this <code>UID</code> to | ||
| 228 | * | ||
| 229 | * @throws IOException if an I/O error occurs while performing | ||
| 230 | * this operation | ||
| 231 | */ | ||
| 232 | public void write(DataOutput out) throws IOException { | ||
| 233 | out.writeInt(unique); | ||
| 234 | out.writeLong(time); | ||
| 235 | out.writeShort(count); | ||
| 236 | } | ||
| 237 | |||
| 238 | /** | ||
| 239 | * Constructs and returns a new <code>UID</code> instance by | ||
| 240 | * unmarshalling a binary representation from an | ||
| 241 | * <code>DataInput</code> instance. | ||
| 242 | * | ||
| 243 | * <p>Specifically, this method first invokes the given stream's | ||
| 244 | * {@link DataInput#readInt()} method to read a <code>unique</code> value, | ||
| 245 | * then it invoke's the stream's | ||
| 246 | * {@link DataInput#readLong()} method to read a <code>time</code> value, | ||
| 247 | * then it invoke's the stream's | ||
| 248 | * {@link DataInput#readShort()} method to read a <code>count</code> value, | ||
| 249 | * and then it creates and returns a new <code>UID</code> instance | ||
| 250 | * that contains the <code>unique</code>, <code>time</code>, and | ||
| 251 | * <code>count</code> values that were read from the stream. | ||
| 252 | * | ||
| 253 | * @param in the <code>DataInput</code> instance to read | ||
| 254 | * <code>UID</code> from | ||
| 255 | * | ||
| 256 | * @return unmarshalled <code>UID</code> instance | ||
| 257 | * | ||
| 258 | * @throws IOException if an I/O error occurs while performing | ||
| 259 | * this operation | ||
| 260 | */ | ||
| 261 | public static UID read(DataInput in) throws IOException { | ||
| 262 | int unique = in.readInt(); | ||
| 263 | long time = in.readLong(); | ||
| 264 | short count = in.readShort(); | ||
| 265 | return new UID(unique, time, count); | ||
| 266 | } | ||
| 267 | } | ||