User Guide


Parallelize Data - OpenMP Counted Loops

When tasks are loop iterations, and the iterations are over a range of values that are known before the loop starts, the loop is easily expressed in OpenMP.
Consider the following annotated serial C/C++ loop:
    ANNOTATE_SITE_BEGIN(sitename);         for (int i = lo; i < hi; ++i) {             ANNOTATE_ITERATION_TASK(taskname);                 statement;         }     ANNOTATE_SITE_END();
OpenMP makes it easy to introduce parallelism into loops. With C or C++ programs, add the
omp parallel for
pragma immediately before the C/C++
...   #pragma omp parallel for for (int i = lo; i < hi; ++i) {       statement;   }
Consider the following annotated Fortran serial loop:
 call annotate_site_begin("sitename") do i = 1, N     call annotate_iteration_task("taskname")           statement end do call annotate_site_end
With Fortran programs, add the
!$omp parallel do
directive immediately before the Fortran
...    !$omp parallel do do i = 1, N         statement end do    !$omp end parallel do
The OpenMP compiler support encapsulates the parallel construct. The rules for capturing the locals can be defaulted or specified as part of the pragma or directive. The loop control variable defaults to being private so each iteration sees its allotted value.

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