How to detect if the VM is running with compact refs from within the VM (no agent)?

[Uwe Schindler]

Hi Dawid,

Can we not simply use that interface from runtime to get the MXBean value, maybe with reflection?:
http://goo.gl/2mBUe

Uwe

-----
Uwe Schindler
uschindler at apache.org 
Apache Lucene PMC Member / Committer
Bremen, Germany
http://lucene.apache.org/


> -----Original Message-----
> From: hotspot-compiler-dev-bounces at openjdk.java.net [mailto:hotspot-
> compiler-dev-bounces at openjdk.java.net] On Behalf Of Dawid Weiss
> Sent: Wednesday, March 14, 2012 9:44 AM
> To: Krystal Mok
> Cc: hotspot compiler
> Subject: Re: How to detect if the VM is running with compact refs from within
> the VM (no agent)?
> 
> Thanks Kris!
> 
> I thought about parsing command-line but I wasn't sure about the runtime --
> can it switch to compressed OOPS on its own (or rather: is there a heuristic to
> switch to compressed OOPS or is it always full refs in 64 bit mode unless an
> explicit command line option's been given)?
> 
> Dawid
> 
> > You could use HotSpotDiagnosticMXBean via JMX to get VM options. An
> > example here [1].
> >
> > If you're trying to get this information from the command line, use:
> >   jinfo -flag UseCompressedOops <pid>
> >
> > HTH,
> > - Kris
> >
> > [1]:  https://gist.github.com/1333043
> >
> >
> > On Wed, Mar 14, 2012 at 4:30 PM, Dawid Weiss <dawid.weiss at gmail.com>
> wrote:
> >>
> >> Hi everyone,
> >>
> >> This has been asked on Apache Lucene JIRA and I admit I don't know
> >> the
> >> answer:
> >>
> >> Is there a way to detect the reference size (which boils down to
> >> compact vs. full reference on 64 bit machines) from within Java?
> >>
> >> I assume the VM starts without an agent so Instrumentation is not
> >> available. I'd appreciate a comment if somebody knows right away
> >> (even if it's a: "no"), otherwise I'll go through the sources and try
> >> to figure it out on my own.
> >>
> >> Thanks,
> >> Dawid
> >
> >