Re: Note on 109327

[Dmitry Antipov]

On 07/31/2012 05:33 PM, Tom Tromey wrote:

> Dmitry> Yes. I'm always thinking about improving internal stuff, GC at first.
> Dmitry> For me, the main motivation for BVAR, KVAR, FVAR etc. is the ability
> Dmitry> to catch the moment when the pointer (e.g. Lisp_Object) within buffer,
> Dmitry> or keyboard, of frame, etc. is read or written, which may be useful
> Dmitry> to implement write barriers (see, for exmaple,
> Dmitry> http://www.hoelzle.org/publications/write-barrier.pdf, but do not
> Dmitry> get confused with http://en.wikipedia.org/wiki/Memory_barrier).
>
> I think to do this well you will need separate macros for getting and
> setting.

Sure, but it's almost impossible to do this at once. At the very beginning,
it's possible to "overestimate" barrier assuming that each XVAR (obj, field)
changes FIELD in OBJ; in the future, reads and writes may be separated, thus
giving a precise write barrier.

Dmitry