Re: [rvm-research] How to record objects' read/write times

On 11/05/15 17:53, 王晨曦 wrote:
> Hi,every one
>
>    I want to record objects' read and write times. As far as I know,
> the Write Barrier is inserted before every Pointer update( object
> assignment ), so I can modify the Write Barrier to record the
> reference  times of the source object. But I know the reference times
> is not equal to the write times of the   source object. Such as:
>
> class a{
>    ........
> }
>
> class b{
>
> a test =new a();
>
> double array_double[ ];
> int   array_int[];
>
> ....
> }
>
>
> and the write barrier will only be inserted before the: (Is this right ?)
>
> b.test=a ; //pointer update
>
> but these assignment below will be ignored. But I think these
> assignments will contribute the main read/write times.
>
> for(i=0;i<Const;i++)
>     array[i]=...
>     array_int[i]===
>

If you look at the MutatorContext class you will see that there is not 
just one write barrier, but one per type plus a couple of special cases, 
so there should be opportunities to instrument every field access.

I can't emphasize Eliot's point (3) enough: be very careful of the code 
you invoke in a barrier.  You need to be certain you don't trigger 
another barrier, and if you are instrumenting all types you must use the 
methods in org.mmtk.vm.Barriers to do *all* heap writes.

Regards,
Robin

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