JIT and invalidation

[Jeroen Frijters]

Hi Rémi,

I think that even on Hotspot you can't guarantee it. The final optimized compiled code is probably safe, but the various intermediate forms most likely aren't. For example, I don't know for sure, but I assume the Hotspot bytecode interpreter can safepoint at any bytecode. Then there is also the interpreted lambda form, which is quite complicated and very likely to trigger a safepoint somewhere.

Regards,
Jeroen

> -----Original Message-----
> From: Remi Forax [mailto:forax at univ-mlv.fr]
> Sent: Monday, February 17, 2014 9:27
> To: Jeroen Frijters; Da Vinci Machine Project
> Subject: Re: JIT and invalidation
> 
> On 02/17/2014 08:53 AM, Jeroen Frijters wrote:
> > Hi Rémi,
> >
> > I believe this is not actually safe. There is no guarantee that when
> SwitchPoint.invalidateAll() returns that all calls to GET_BYTE or
> PUT_BYTE that were in flight have completed.
> >
> > Regards,
> > Jeroen
> 
> yes, you're right,
> I've forgotten to say that this code is Hotspot specific.
> 
> So let me re-phrase, I believe this code is safe if the VM is Hotspot
> because invalidation is done at a safepoint so no GET_BYTE/PUT_BYTE can
> be in flight.
> 
> Rémi
> 
> >
> >> -----Original Message-----
> >> From: mlvm-dev-bounces at openjdk.java.net [mailto:mlvm-dev-
> >> bounces at openjdk.java.net] On Behalf Of Remi Forax
> >> Sent: Sunday, February 16, 2014 22:54
> >> To: Da Vinci Machine Project
> >> Subject: JIT and invalidation
> >>
> >> Hi John, Hi Christian, Hi all,
> >> I don't know if you can test this little code, but when I run it on
> >> my laptop (linux 64bits) it can terminate in 45s or 2 minutes, it
> >> seems that it depends on the order the JIT compiles the method
> handles.
> >>     https://gist.github.com/forax/9041030
> >>
> >> Sometimes it also PrintCompilation can also prints 'COMPILE SKIPPED:
> >> invalid non-klass dependency'.
> >>
> >> BTW, the code allows to safely* map and unmap a 32G file without not
> >> always paying the cost of the runtime check that test if the array is
> >> unmaped or not :)
> >>
> >> cheers,
> >> Rémi
> >> * I believe.
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