Hi Michael,
OpenMP is a very different beast, and was developed to help get over the
shortcomings that languages like C and FORTRAN have with respect to parallel
and concurrent programming (pthreads were about all there was before OpenMP).
OpenMP lets you specify regions of code that should be run in multiple threads
at once, each with a unique ID. Here is an example of (part of) a parallel
merge sort I've been working on
> static void
> pmergesort(long int * in, long int * tmp, long int n, int nthread)
> {
> long int nhalf = n/2;
>
> if(n <= N_small)
> {
> insertsort1(in, n);
> return;
> }
>
> if(nthread > 1)
> {
> #pragma omp parallel num_threads(2)
> {
> if(omp_get_thread_num() == 0)
> pmergesort(tmp, in, nhalf, nthread>>1);
> else pmergesort(tmp+nhalf, in+nhalf, n-nhalf, nthread>>1);
> }
> } else {
> mergesort3(tmp, in, nhalf);
> mergesort3(tmp+nhalf, in+nhalf, n-nhalf);
> }
>
> merge( tmp, in, nhalf, n);
> }
The approach that Control.Concurrent takes is very different, preferring a
style where the programmer says what things might be advantageous to run in
parallel, but the runtime makes no guarantees that they will be, allowing the
programmer to break work down into smaller chunks, and letting the runtime sort
out which parts should be run concurrently. This allows for a much easier style
of parallel programming, but is only really possible in a pure language like
Haskell.
On a side note, the Cilk language, which adds a small number of keywords like
fork and sync to the C language takes an approach closer to what
Control.Parallel does, but it's not a graceful, and IMO not as easy to use.
Hope that helps. I've been having a lot of fun over the last few weeks playing
with OpenMP for a university assignment, and I've got to say I greatly prefer
the haskell way of doing things.
Cheers,
Alex Mason
On 27/05/2011, at 10:23, michael rice wrote:
> Are the tools of Control.Parallel comparable to OpenMP?
>
> Michael
>
> --- On Thu, 5/26/11, michael rice <[email protected]> wrote:
>
> From: michael rice <[email protected]>
> Subject: Re: [Haskell-cafe] Parallel compilation and execution?
> To: "David Virebayre" <[email protected]>
> Cc: "Daniel Fischer" <[email protected]>,
> [email protected]
> Date: Thursday, May 26, 2011, 9:32 AM
>
> Fair question. I copied the parallel version from:
>
> http://www.haskell.org/ghc/docs/6.6/html/users_guide/lang-parallel.html
>
> but pulled the non-parallel version from a text.
>
> Michael
>
>
> --- On Thu, 5/26/11, David Virebayre <[email protected]> wrote:
>
> From: David Virebayre <[email protected]>
> Subject: Re: [Haskell-cafe] Parallel compilation and execution?
> To: "michael rice" <[email protected]>
> Cc: [email protected], "Daniel Fischer"
> <[email protected]>
> Date: Thursday, May 26, 2011, 8:56 AM
>
>
>
> 2011/5/26 michael rice <[email protected]>
> Thank, Daniel
>
> Multiple threads are in evidence in my system monitor, but I wonder why I'm
> getting two different answers, one twice the other. The first is the parallel
> solution and the second is the non.
>
> Why do you add n1+n2+1 in the parallel program, but only n1+n2 in the
> non-parallel one ?
>
>
> Michael
>
> ===========
>
> {-
> import Control.Parallel
>
> nfib :: Int -> Int
> nfib n | n <= 1 = 1
> | otherwise = par n1 (pseq n2 (n1 + n2 + 1))
> where n1 = nfib (n-1)
> n2 = nfib (n-2)
> -}
>
> nfib :: Int -> Int
> nfib n | n <= 1 = 1
> | otherwise = nfib (n-1) + nfib (n-2)
>
> main = do putStrLn $ show $ nfib 39
>
> =============
>
> [michael@hostname ~]$ ghc --make -threaded nfib.hs
> [1 of 1] Compiling Main ( nfib.hs, nfib.o )
> Linking nfib ...
> [michael@hostname ~]$ ./nfib +RTS -N3
> 204668309
> [michael@hostname ~]$ ghc --make nfib.hs
> [1 of 1] Compiling Main ( nfib.hs, nfib.o )
> Linking nfib ...
> [michael@hostname ~]$ ./nfib
> 102334155
> [michael@hostname ~]$
>
>
>
> -----Inline Attachment Follows-----
>
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