[Haskell-cafe] Dynamic thread management?

[Bayley, Alistair]

> From: haskell-cafe-bounces at haskell.org 
> [mailto:haskell-cafe-bounces at haskell.org] On Behalf Of Hugh Perkins
> 
> Not many replies on this thread?  Am I so wrong that no-one's 
> even telling me?  I find it hard to believe that if there 
> were obvious errors in the proposition that anyone would 
> resist pointing them out to me ;-)

Well, I vaguely recall a study which analysed a number of programs and
determined that there was not a lot of inherent parallelism in them, so
the effort to automate parallelism wouldn't have much payoff.  Wait a
sec...

This isn't it, but seems relevant:
http://www.detreville.org/papers/Limits.pdf

Here you go:
http://citeseer.ist.psu.edu/tremblay95impact.html


> So, that leaves a couple of possibilites: some people are 
> agreeing, but see no point in saying; or noone cares, because 
> we all only have 1 or 2 core machines.

Well, the Harris/Singh paper summarises the common problems:
 - not many programs are inherently parallel
 - parallelism must be quite coarse to offset overheads
   (which I think is the problem with expecting things like map and fold
to parallelised automagically; they're just too small grained for it to
be worthwhile)
 - lazy evaluation makes it harder

Basically, it's harder than it sounds.

This is where NDP looks good. Although you have to explicitly label
parallel operations, you get to use your functional tools like map and
fold, etc.

Alistair
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