Routines for Nesting Support

Routines for Nesting Support in OpenMP 3.0

New environment variables:

OMP_MAX_ACTIVE_LEVELS
OMP_THREAD_LIMIT

The above environment variables are described in Sections 4.7 and 4.8 of the OpenMP specification.

New runtime routines:

omp_get_thread_limit
omp_set_max_active_levels
omp_get_max_active_levels
omp_get_level
omp_get_ancestor_thread_num
omp_get_team_size
omp_get_active_level

The above environment variables are described in Section 3.2 of the OpenMP specification

Example (Fortran):

      program test
      use omp_lib

      call omp_set_dynamic (.false.)
      call omp_set_nested (.true.)
      call omp_set_num_threads (4)
      call omp_set_max_active_levels (3)

!$omp parallel private (levels)
!$omp single
           levels = omp_get_max_active_levels()
           print *, "Par #1: Max active levels =", levels,
     &              "In parallel =", omp_in_parallel()
!$omp end single

!$omp parallel private (levels)
!$omp master
           levels = omp_get_max_active_levels()
           print *, "Par #2: Max active levels =", levels,
     &              "In parallel =", omp_in_parallel()
           call omp_set_max_active_levels (1)
           print *, "Par #2: Max active levels =", levels,
     &              "In parallel =", omp_in_parallel()
!$omp end master

!$omp parallel private (levels)
!$omp single
           levels = omp_get_max_active_levels()
           print *, "Par #3: Max active levels =", levels,
     &              "In parallel =", omp_in_parallel()
!$omp end single
!$omp end parallel
!$omp end parallel
!$omp end parallel
      end


% f90 -xopenmp -xO3 test.f
% a.out
 Par #1: Max active levels = 3 In parallel = T
 Par #2: Max active levels = 3 In parallel = T
 Par #2: Max active levels = 3 In parallel = T
 Par #3: Max active levels = 3 In parallel = T
 Par #2: Max active levels = 3 In parallel = T
 Par #2: Max active levels = 3 In parallel = T
 Par #3: Max active levels = 3 In parallel = T
 Par #3: Max active levels = 3 In parallel = T
 Par #3: Max active levels = 3 In parallel = T
 Par #3: Max active levels = 3 In parallel = T
 Par #3: Max active levels = 3 In parallel = T
 Par #3: Max active levels = 3 In parallel = T
 Par #2: Max active levels = 3 In parallel = T
 Par #2: Max active levels = 3 In parallel = T
 Par #2: Max active levels = 3 In parallel = T
 Par #2: Max active levels = 3 In parallel = T
 Par #3: Max active levels = 3 In parallel = T
 Par #3: Max active levels = 3 In parallel = T
 Par #3: Max active levels = 3 In parallel = T
 Par #3: Max active levels = 3 In parallel = T
 Par #3: Max active levels = 3 In parallel = T
 Par #3: Max active levels = 3 In parallel = T
 Par #3: Max active levels = 3 In parallel = T
 Par #3: Max active levels = 3 In parallel = T
 Par #3: Max active levels = 3 In parallel = T

Example (C/C++):

#include "omp.h"
#include <stdio.h>

int main()
{
  omp_set_dynamic(0);
  omp_set_nested(1);

  #pragma omp parallel num_threads(2)
  {
    if (omp_get_thread_num() == 0) {
        #pragma omp parallel num_threads(2)
        {
          if (omp_get_thread_num() == 1) {
              printf ("Y: omp_get_level() = %d\n",
                      omp_get_level());
              printf ("Y: omp_get_active_level() = %d\n",
                      omp_get_active_level());
              printf ("Y: omp_get_ancestor_thread_num(1) = %d\n",
                      omp_get_ancestor_thread_num(1));
              printf ("Y: omp_get_ancestor_thread_num(2) = %d\n",
                      omp_get_ancestor_thread_num(2));
          }
        }
    }

  }
}


% cc -xopenmp -xO3 test.c
% a.out
Y: omp_get_level() = 2
Y: omp_get_active_level() = 2
Y: omp_get_ancestor_thread_num(1) = 0
Y: omp_get_ancestor_thread_num(2) = 1

OpenMP 3.0 Features in Express 7.08

Routines for Nesting Support

Routines for Nesting Support in OpenMP 3.0

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