Re: [rvm-research] primitive read barriers

Hi Shoaib,

If you check in ExpandRuntimeServices, you'll see that (for the opt 
compiler at least) GETFIELD barriers are only implemented for Object 
fields.  MMTk definitely has support (and we exercise it regularly via 
the harness), but JikesRVM not so much.

You can see in that class that implementing the barriers would be fairly 
simple (look at the PUTFIELD code), but getting it to *work* ... well, 
that's a different question.  I'd suggest you would need a way to 
exclude all VM code from the barriers and work from there.  Read 
barriers are HARD.

cheers


On 26/11/17 06:52, Shoaib Akram wrote:
> Hi All,
>
> I want to barrier all read operations in MMTk. But when I enable read barriers, only the reference read barrier work.
>
> I have used primitive write barriers in Jikes before. For them to work, I had to specify the needsPrimitiveWriteBarrier() is the constraints file of my Plan. Then, I had to declare the method that executes the barrier code in my Mutator. I am doing the same for enabling read barriers.
>
> Is there a reason primitive read barriers don’t work in Jikes? I thought the support was added quite a while ago for primitive read and write barriers.
>
> Also the PlanConstraints file have methods such as needsBooleanReadBarrier and so on. So, I assume there is support for primitive read barriers, or no?
>
> Regards,
> Shoaib.
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