Mo DeJong wrote,
> There seems to be a really serious bug in the
> System.identityHashCode() method in all > JDK 1.2 releases
> derived from Sun code. The problem only shows up in "high
> load" situations. Basically, two different Java objects of
> the same class can return the exact same unique id from the
> System.identityHashCode() method.
Why is this a bug? The only requirement on a hashCode (system
or otherwise) is that two == or .equal() objects should have
the same hashCode. There's no requirement that != or !.equal()
objects should have different hashCodes.
Apart from anything else, hashCodes are ints, so there are at
most 2^32 distinct ones. A 64 bit implementation could support
more that 2^32 objects, in which case there'd have to be some collisions.
> So far, I have identified a couple of workarounds. I could
> just require that everyone use a JDK 1.1 release. I could
> also require that people use Kaffe (it does not have the
> bug). The final option would be to write my own UID() method
> that would try to do something to detect a duplicate id and
> generate a unique one.
>
> Comments anyone?
You shouldn't expect System.identityHashCode() to be usable as
a UID. Assuming otherwise is non-portable ... as you've just
discovered.
Cheers,
Miles
--
Miles Sabin Cromwell Media
Internet Systems Architect 5/6 Glenthorne Mews
+44 (0)20 8817 4030 London, W6 0LJ, England
[EMAIL PROTECTED] http://www.cromwellmedia.com/
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