OpenMP and Multithreading: Difference between revisions

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(Created page with "=== simple parallelization === * brute force loop parallelization with direct access to elements using [] (for instance with int[], vectors<T>, valarray<T>...) <source lang="cp...")
 
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     {
     {
#pragma omp single nowait
#pragma omp single nowait
{
     foo(It);
     foo(It);
}
     }
     }
}
}
</source>
* calculating a sum
<source lang="cpp">
int count = 0;
Container cont;
#pragma omp parallel for
for (int i = 0; i < cont.size(); ++i)
  {
#pragma omp atomic
    count += cont[i];
  }
</source>
</source>

Revision as of 11:06, 7 April 2011

simple parallelization

  • brute force loop parallelization with direct access to elements using [] (for instance with int[], vectors<T>, valarray<T>...)

<source lang="cpp"> Container cont;

  1. pragma omp parallel for

for(int i=0; i < cont.size(); i++)

  foo(cont[i]);

</source>


  • with stl iterators on containers, provided foo() does independent processes:

<source lang="cpp"> Container cont; Container::iterator It;

  1. pragma omp parallel private(It)

{

   for(It = cont->begin(); It != cont->end(); It++)
   {
  1. pragma omp single nowait
    foo(It);
   }

} </source>

  • calculating a sum

<source lang="cpp"> int count = 0; Container cont;

  1. pragma omp parallel for

for (int i = 0; i < cont.size(); ++i)

 {
  1. pragma omp atomic
   count += cont[i];
 }

</source>