Uuid.java

/**************************************************************************************
 * Copyright (c) Jonas Bon�r, Alexandre Vasseur. All rights reserved.                 *
 * http://aspectwerkz.codehaus.org                                                    *
 * ---------------------------------------------------------------------------------- *
 * The software in this package is published under the terms of the LGPL license      *
 * a copy of which has been included with this distribution in the license.txt file.  *
 **************************************************************************************/
package org.codehaus.aspectwerkz.proxy;

/**
 * NOTE:
 * <p/>
 * This code is based on code from the [Plasmid Replication Engine] project.
 * <br/>
 * Licensed under [Mozilla Public License 1.0 (MPL)].
 * <p/>
 * Original JavaDoc:
 * <p/>
 * Our distributed objects are generally named most efficiently (and cleanly)
 * by their UUID's. This class provides some static helpers for using UUID's.
 * If it was efficient to do in Java, I would make the uuid an normal class
 * and use instances of it. However, in current JVM's, we would end up using an
 * Object to represent a long, which is pretty expensive. Maybe someday. ###
 * <p/>
 * UUID format: currently using currentTimeMillis() for the low bits. This uses
 * about 40 bits for the next 1000 years, leaving 24 bits for debugging
 * and consistency data. I'm using 8 of those for a magic asci 'U' byte.
 * <p/>
 * Future: use one instance of Uuid per type of object for better performance
 * and more detailed info (instance could be matched to its uuid's via a map or
 * array). This all static version bites.###
 */
public final class Uuid {

    public static final long UUID_NONE = 0;
    public static final long UUID_WILD = -1;
    public static final long UUID_MAGICMASK = 0xff << 56;
    public static final long UUID_MAGIC = 'U' << 56;

    protected static long lastTime;

    /**
     * Generate and return a new Universally Unique ID.
     * Happens to be monotonically increasing.
     */
    public synchronized static long newUuid() {
        long time = System.currentTimeMillis();

        if (time <= lastTime) {
            time = lastTime + 1;
        }
        lastTime = time;
        return UUID_MAGIC | time;
    }

    /**
     * Returns true if uuid could have been generated by Uuid.
     */
    public static boolean isValid(final long uuid) {
        return (uuid & UUID_MAGICMASK) == UUID_MAGIC
               && (uuid & ~UUID_MAGICMASK) != 0;
    }
}