Re: FW: [Bug-gnubg] Simple multi-threading... Cache

[Jim Segrave]

On Tue 23 Jan 2007 (08:44 -0000), Ian Shaw wrote:
>  
> 
> Jonathan Kinsey wrote on 22 January 2007 18:57
> > 
> > After some further testing, I was getting some small differences in 
> > the results.  I found the global eval cache needed to be protected to 
> > stop multiple accesses (from different threads), but am still getting 
> > differences.
> > 
> > Does anyone know if adding positions to the cache from multiple 
> > threads (i.e. further ahead in the game), could cause differences in 
> > the final results?
> > 
> > I may need to have a separate cache for each thread, but this would 
> > probably lead to many positions being evaluated more than once?
> > 
> > I'm not sure exactly how the cache works so any thoughts would be 
> > helpful!
> 
> Is the context/ply of the evaluation stored in the cache?
> 
> If not, an evaluation stored by thread A at 1-ply could be accessed by
> thread B at 0 or 2 ply, thus leading to slightly different results.

Yes - cache entries are indexed by position and evaluation (although,
as I recall, it's evaluation type and no. of plies, so if you were
doing 2-ply evaluations with different move filters for different
players, I think it would not see the difference in evaluations.

-- 
Jim Segrave           address@hidden