OpenMP and Multithreading

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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>