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Date: Thu, 07 Mar 2013 17:22:03 -0500
From: "Peter C. Chapin" <PChapin@vtc.vsc.edu>
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Newsgroups: comp.lang.ada
Subject: Re: Ada and OpenMP
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 <87k3pjht79.fsf@ludovic-brenta.org>
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Date: 2013-03-07T17:22:03-05:00
List-Id: <comp.lang.ada>

OpenMP is a different animal than Ada tasks. It provides fine grained 
parallelism where, for example, it is possible to have the compiler 
automatically parallelize a loop. In C:

#pragma omp parallel for
for( i = 0; i < MAX; ++i ) {
   array[i]++;
}

The compiler automatically splits the loop iterations over an 
"appropriate" number of threads (probably based on the number of cores).

In Ada one might write, perhaps

pragma OMP(Parallel_For)
for I in 1 .. MAX loop
   A(I) := A(I) + 1
end loop;

Doing this with Ada tasks in such a way that it uses an optimal number 
of threads on each execution (based on core count) would be much more 
complicated, I should imagine. Please correct me if I'm wrong!

OpenMP has various other features, some of which could be done naturally 
with tasks, but much of what OpenMP is about is semi-automatic fine 
grained parallelization. It is to Ada tasking what Ada tasking is to the 
explicit handling of locks, etc.

Peter

On 03/07/2013 03:04 PM, Ludovic Brenta wrote:
> Rego, P. writes on comp.lang.ada:
>> I'm trying some exercises of parallel computing using that pragmas
>> from OpenMP in C, but it would be good to use it also in Ada. Is it
>> possible to use that pragmas from OpenMP in Ada? And...does gnat gpl
>> supports it?
>
> Why would you use pragmas when Ada supports tasking directly in the
> language?
>