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/*
* @(#) UniqueIdGenerator.java
*
* Copyright 2000-2001 by iPlanet/Sun Microsystems, Inc.,
* 901 San Antonio Road, Palo Alto, California, 94303, U.S.A.
* All rights reserved.
*
* This software is the confidential and proprietary information
* of iPlanet/Sun Microsystems, Inc. ("Confidential Information").
* You shall not disclose such Confidential Information and shall
* use it only in accordance with the terms of the license
* agreement you entered into with iPlanet/Sun Microsystems.
*/
package com.sun.enterprise.instance;
import java.util.logging.Logger;
import java.util.logging.Level;
import com.sun.logging.LogDomains;
/**
* Generates unique id for an application or stand alone ejb module.
*
* It uses the low order 6 bytes of the system current time. The remaining
* 2 bytes are reserved for the beans inside the application and stand
* alone ejb module.
*
* The unique id generated by this generator will eventually wrap after
* 2^48 milli-seconds (8,925.25 years).
*
* The two bytes reserved for the beans in the application or stand alone ejb
* module will allow max 2^16 (65,536) beans.
*
* @author Nazrul Islam
* @since JDK1.4
*/
public class UniqueIdGenerator {
/** last unique id given out by this id generator */
private long _lastUid = 0;
/** the singleton instance */
private static UniqueIdGenerator _instance = null;
private static Logger _logger = LogDomains.getLogger(LogDomains.CORE_LOGGER);
static {
_instance = new UniqueIdGenerator();
}
private UniqueIdGenerator() { }
/**
* Returns the singleton instance of this class.
*
* @return the singleton instance
*/
public static UniqueIdGenerator getInstance() {
return _instance;
}
/**
* Returns the next unique id for an application or
* stand alone ejb module.
*
* @return the next unique id
*/
public long getNextUniqueId() {
synchronized (this) {
while (true) {
long uid = System.currentTimeMillis();
// uses the low order 6 bytes as unique id;
// remaining 2 bytes are reserved for the beans inside the app
uid = (uid << 16);
// ensures that we have a unique id
if (this._lastUid != uid) {
this._lastUid = uid;
break;
} else {
try {
Thread.currentThread().sleep(1);
} catch (InterruptedException ie) {
// log debug msg here
_logger.log(Level.WARNING,"Thread.sleep interrupted ",ie);
}
}
}
return this._lastUid;
}
}
}
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