10.2. default(none) Clause

The following example distinguishes the variables that are affected by the default(none) clause from those that are not.

Beginning with OpenMP 4.0, variables with const-qualified type and no mutable member are no longer predetermined shared. Thus, these variables (variable c in the example) need to be explicitly listed in data-sharing attribute clauses when the default(none) clause is specified.

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

/*
* name: default_none.1
* type: C
*/
#include <omp.h>
int x, y, z[1000];
#pragma omp threadprivate(x)

void default_none(int a) {
  const int c = 1;
  int i = 0;

  #pragma omp parallel default(none) private(a) shared(z, c)
  {
     int j = omp_get_num_threads();
          /* O.K.  - j is declared within parallel region */
     a = z[j];   /* O.K.  - a is listed in private clause */
                 /*       - z is listed in shared clause */
     x = c;      /* O.K.  - x is threadprivate */
                 /*       - c has const-qualified type and
                              is listed in shared clause */
     z[i] = y;   /* Error - cannot reference i or y here */

  #pragma omp for firstprivate(y)
         /* Error - Cannot reference y in the firstprivate clause */
     for (i=0; i<10 ; i++) {
        z[i] = i; /* O.K. - i is the loop iteration variable */
     }

     z[i] = y;   /* Error - cannot reference i or y here */
  }
}

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

! name: default_none.1
! type: F-fixed
      SUBROUTINE DEFAULT_NONE(A)
      INCLUDE "omp_lib.h"     ! or USE OMP_LIB

      INTEGER A

      INTEGER X, Y, Z(1000)
      COMMON/BLOCKX/X
      COMMON/BLOCKY/Y
      COMMON/BLOCKZ/Z
!$OMP THREADPRIVATE(/BLOCKX/)

        INTEGER I, J
        i = 1

!$OMP   PARALLEL DEFAULT(NONE) PRIVATE(A) SHARED(Z) PRIVATE(J)
          J = OMP_GET_NUM_THREADS();
                   ! O.K.  - J is listed in PRIVATE clause
          A = Z(J) ! O.K.  - A is listed in PRIVATE clause
                   !       - Z is listed in SHARED clause
          X = 1    ! O.K.  - X is THREADPRIVATE
          Z(I) = Y ! Error - cannot reference I or Y here

!$OMP DO firstprivate(y)
    ! Error - Cannot reference y in the firstprivate clause
          DO I = 1,10
             Z(I) = I ! O.K. - I is the loop iteration variable
          END DO


          Z(I) = Y    ! Error - cannot reference I or Y here
!$OMP   END PARALLEL
      END SUBROUTINE DEFAULT_NONE