Re: boost.threads

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