9.3. Binding of barrier Regions

The binding rules call for a barrier region to bind to the closest enclosing parallel region.

In the following example, the call from the main program to sub2 is conforming because the barrier region (in sub3 ) binds to the parallel region in sub2 . The call from the main program to sub1 is conforming because the barrier region binds to the parallel region in subroutine sub2 .

The call from the main program to sub3 is conforming because the barrier region binds to the implicit inactive parallel region enclosing the sequential part. Also note that the barrier region in sub3 when called from sub2 only synchronizes the team of threads in the enclosing parallel region and not all the threads created in sub1 .

//%compiler: clang
//%cflags: -fopenmp

/*
* name: barrier_regions.1
* type: C
*/
void work(int n) {}

void sub3(int n)
{
  work(n);
  #pragma omp barrier
  work(n);
}

void sub2(int k)
{
  #pragma omp parallel shared(k)
    sub3(k);
}

void sub1(int n)
{
  int i;
  #pragma omp parallel private(i) shared(n)
  {
    #pragma omp for
    for (i=0; i<n; i++)
      sub2(i);
  }
}

int main()
{
  sub1(2);
  sub2(2);
  sub3(2);
  return 0;
}

!!%compiler: gfortran
!!%cflags: -fopenmp

! name: barrier_regions.1
! type: F-fixed
      SUBROUTINE WORK(N)
        INTEGER N
      END SUBROUTINE WORK

      SUBROUTINE SUB3(N)
      INTEGER N
        CALL WORK(N)
!$OMP   BARRIER
        CALL WORK(N)
      END SUBROUTINE SUB3

      SUBROUTINE SUB2(K)
      INTEGER K
!$OMP   PARALLEL SHARED(K)
          CALL SUB3(K)
!$OMP   END PARALLEL
      END SUBROUTINE SUB2


      SUBROUTINE SUB1(N)
      INTEGER N
        INTEGER I
!$OMP   PARALLEL PRIVATE(I) SHARED(N)
!$OMP     DO
          DO I = 1, N
            CALL SUB2(I)
          END DO
!$OMP   END PARALLEL
      END SUBROUTINE SUB1

      PROGRAM EXAMPLE
        CALL SUB1(2)
        CALL SUB2(2)
        CALL SUB3(2)
      END PROGRAM EXAMPLE