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From Adkins Kendall <Kendall.Adk...@HCAhealthcare.com>
Subject RE: [id] UUID update
Date Thu, 04 Mar 2004 04:32:01 GMT
And I thought I was helping! Thanks. :)

-----Original Message-----
From: Marc Slemko [mailto:marcs@znep.com]
Sent: Wednesday, March 03, 2004 10:27 PM
To: Jakarta Commons Developers List
Subject: RE: [id] UUID update


On Wed, 3 Mar 2004, Adkins Kendall wrote:

> Here is a UID Generator we are using.  Part of the UID contains the hash
of
> a final static object instance.  In this way, while a JVM is up you are
> assured no other objects can occupy the same memory address.  We have had
no
> difficulty with it under heavy load across 4 servers each with three JVMs.

Unfortunately, that is incorrect.

Nearly every system that runs a JVM uses virtual memory, so each process has
its own virtual address address space.  In such a case, especially if
classes are loaded in the same order, etc., it is very likely that the
address will not be unique across different JVMs on a machine.

See the bug at
http://developer.java.sun.com/developer/bugParade/bugs/4212322.html
for an example of where someone at Sun thought the same thing, with
a longer description of why it doesn't work and an example that shows it.

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