[PPL-devel] OpenMP & PPL

[Enea Zaffanella]

On 31/12/2017 17:33, Thomas LE MÉZO wrote:
>
> Dear Enea, Dear all,
>
>
> I tried recently to implement a multi-thread version of my thesis code 
> using PPL library. I used OpenMP and the last version of ppl on devel 
> git branch as I read you have been working on a thread-safe 
> implementation (thread-safe option with configure). I didn't succeed 
> in writing a correct program; see for instance this simple code that 
> return a segmentation fault :
>
>
> #include <omp.h>
>
> namespace PPL = Parma_Polyhedra_Library;
>
>
> int main(){
>
> #pragma omp parallel for
>     for(int i=0; i<1000; i++){
> PPL::C_Polyhedron ph1(3); // => segmentation fault at line 83 of 
> Linear_Expression.cc
> PPL::C_Polyhedron ph2(3);
>         ph1.intersection_assign(ph2);
>     }
>     return 0;
> }
>
> Would you have any idea about what is wrong?
>

Each thread should be properly initialized by creating a 
PPL::Thread_Init object (and finalized by destroying it).
See for instance test01() in tests/Polyhedron/threadsafe1.cc
As an alternative, you could use the make_threadable wrapper (see 
test02() in the same test).

> Is PPL compatible with using OpenMP?
>

I never tried using it with OpenMP ... however, as long as thread 
initializations (and finalizations) are performed as suggested above, 
things should be working (there is also a library initialization part, 
but that is automatically done when working in C++).

In you code, I would try adding

   PPL::Thread_Init thread_init;

as the very first line of the loop body.
This would maybe create more init objects than needed,
but (if I remember correctly) that should not be a problem.

Let us know how it goes.

Enea

>
> Thanks a lot in advance,
>
> Thomas
>
>
>
>
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