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

[Christine Flood]

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
>