From: williamkempf_at_[hidden]
Date: 2001-08-07 12:58:11
--- In boost_at_y..., John Max Skaller <skaller_at_m...> wrote:
> Beman Dawes wrote:
>
> > At 06:07 PM 8/5/2001, John Max Skaller wrote:
> >
> > >Question: does anyone share stack data between threads?
> > >
> > >Reason for asking:
> > >
> > > 1) Bemans model tries to ban this
> > > 2) I objected
> > >
> >
> > My original formulation was confusing because it didn't clearly
distinguish
> > between stack data accessed directly by within its thread (not
shared) and
> > stack data access from another thread via pointer or reference
(shared).
>
> OK.
>
> > >but it occurs to me that on a multi-processor, the constraint
> > >would allow CPU local memory to be used for the stack, which
> > >could be a significant optimisation.
> >
> > Since that would disallow inter-thread pointers or references to
stack
> > objects, I don't think it would allow a conforming thread
implementation.
>
> According to your (reformulated) rules.
> The question is: is the local (unsharable) stack a viable
> implementation,
> and if so, can we ban sharing stack data to allow that
implementation
> without impacting programmers?
>
> Shared memory is expensive, local memory is cheap.
> If threads can run with the stack on 'on board' memory which is on a
> separate
> high speed per CPU bus from main memory, they might run considerably
> faster: such memory can be cached without being flushed, since only
> one CPU can access it.
I wouldn't expect the standard to allow this. To do so safely you'd
have to somehow distinguish between a pointer to this "local memory"
and a normal pointer. Most of us could not live with access
violations caused by passing the wrong pointer type.
However, I see nothing wrong with platform specific extensions that
made use of such local memory.
Bill Kempf