JEP 189: Shenandoah: An Ultra-Low-Pause-Time Garbage Collector

[Vitaly Davidovich]

What's the advantage of not copying and fixing up the pointer in a read
barrier issued by a mutator, ala Azul? Having mutators help out with
copying seems good on the surface.  What's the catch?

Sent from my phone
On Jan 17, 2014 3:43 PM, "Christine Flood" <chf at redhat.com> wrote:

>
> Hi
>
> Thanks for asking the question.  Radio silence was making me paranoid.
>
> There are two obvious approaches to concurrent evacuation.
>
> One way is to trap when anyone tries to read an object in a from region
> and cause that
> object to be evacuated.  That's what Azul does.
>
> Our approach is to have a fowarding pointer associated with an object.
>  The read barrier is just
> a simple additional read to figure out whether the object is where you
> thought
> it was or if it has moved.
>
>
> Our read barriers never cause object copying and we are a software only
> solution.
> This means that we will run anywhere that the other Java collectors do.
>
> You can choose Shenandoah at runtime like you would any other GC.
>
> Christine
>
>
> ----- Original Message -----
> > From: "Vitaly Davidovich" <vitalyd at gmail.com>
> > To: "Roman Kennke" <rkennke at redhat.com>
> > Cc: hotspot-gc-dev at openjdk.java.net
> > Sent: Friday, January 17, 2014 3:19:58 PM
> > Subject: Re: JEP 189: Shenandoah: An Ultra-Low-Pause-Time Garbage
> Collector
> >
> > Any chance you guys can highlight some notable differences between this
> > collector and Azul's C4 collector? I can see both employ read barriers,
> but
> > can't quite make out what else is there.
> >
> > Also, will this also require any changes to kernel in order to support
> the
> > low pause goals? IIRC, Azul had problems with Linux because the memory
> > manager didn't support bulk map/unmap operations, or something like that.
> > This also begs the question of whether this new collector will be biased
> > towards linux/Unix systems, or whether windows will get the same love.
> >
> > Thanks
> >
> > Sent from my phone
> > On Jan 17, 2014 2:31 PM, "Roman Kennke" <rkennke at redhat.com> wrote:
> >
> > Hi there,
> >
> > Sorry being so silent... we are very happy that the Shenandoah JEP has
> > finally been posted and would welcome any comments, questions,
> > discussion from the community.
> >
> > Cheers,
> > Roman
> >
> > Am Mittwoch, den 15.01.2014, 11:49 -0800 schrieb
> > mark.reinhold at oracle.com:
> > > Posted: http://openjdk.java.net/jeps/189
> > >
> > > - Mark
> >
>
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