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Java > Open Source Codes > com > tc > aspectwerkz > proxy > Uuid


1 /*
2  * All content copyright (c) 2003-2006 Terracotta, Inc., except as may otherwise be noted in a separate copyright notice. All rights reserved.
3  */
4 package com.tc.aspectwerkz.proxy;
5
6 /**
7  * NOTE:
8  * <p/>
9  * This code is based on code from the [Plasmid Replication Engine] project.
10  * <br/>
11  * Licensed under [Mozilla Public License 1.0 (MPL)].
12  * <p/>
13  * Original JavaDoc:
14  * <p/>
15  * Our distributed objects are generally named most efficiently (and cleanly)
16  * by their UUID's. This class provides some static helpers for using UUID's.
17  * If it was efficient to do in Java, I would make the uuid an normal class
18  * and use instances of it. However, in current JVM's, we would end up using an
19  * Object to represent a long, which is pretty expensive. Maybe someday. ###
20  * <p/>
21  * UUID format: currently using currentTimeMillis() for the low bits. This uses
22  * about 40 bits for the next 1000 years, leaving 24 bits for debugging
23  * and consistency data. I'm using 8 of those for a magic asci 'U' byte.
24  * <p/>
25  * Future: use one instance of Uuid per type of object for better performance
26  * and more detailed info (instance could be matched to its uuid's via a map or
27  * array). This all static version bites.###
28  */
29 public final class Uuid {
30
31   public static final long UUID_NONE = 0;
32   public static final long UUID_WILD = -1;
33   public static final long UUID_MAGICMASK = 0xff << 56;
34   public static final long UUID_MAGIC = 'U' << 56;
35
36   protected static long lastTime;
37
38   /**
39    * Generate and return a new Universally Unique ID.
40    * Happens to be monotonically increasing.
41    */
42   public synchronized static long newUuid() {
43     long time = System.currentTimeMillis();
44
45     if (time <= lastTime) {
46       time = lastTime + 1;
47     }
48     lastTime = time;
49     return UUID_MAGIC | time;
50   }
51
52   /**
53    * Returns true if uuid could have been generated by Uuid.
54    */
55   public static boolean isValid(final long uuid) {
56     return (uuid & UUID_MAGICMASK) == UUID_MAGIC
57             && (uuid & ~UUID_MAGICMASK) != 0;
58   }
59 }
60
61
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