OpenMP Directives: Work-Sharing Constructs: WORKSHARE Directive

Purpose:

• Fortran only
• The WORKSHARE directive divides the execution of the enclosed structured block into separate units of work, each of which is executed only once.
• The structured block must consist of only the following:
  • array assignments
  • scalar assignments
  • FORALL statements
  • FORALL constructs
  • WHERE statements
  • WHERE constructs
  • atomic constructs
  • critical constructs
  • parallel constructs

See the OpenMP API documentation for additional information, particularly for what comprises a “unit of work”.

Format:

Fortran:

!$OMP WORKSHARE

   structured block

!$OMP END WORKSHARE [ NOWAIT ]

Restrictions:

The construct must not contain any user defined function calls unless the function is ELEMENTAL.

Example: WORKSHARE Directive

Simple array and scalar assigments shared by the team of threads. A unit of work would include: * Any scalar assignment * For array assignment statements, the assignment of each element is a unit of work

Fortran:

      PROGRAM WORKSHARE
 
      INTEGER N, I, J
      PARAMETER (N=100)
      REAL AA(N,N), BB(N,N), CC(N,N), DD(N,N), FIRST, LAST
 
!     Some initializations
      DO I = 1, N
        DO J = 1, N
          AA(J,I) = I * 1.0
          BB(J,I) = J + 1.0
        ENDDO
      ENDDO
 !$OMP PARALLEL SHARED(AA,BB,CC,DD,FIRST,LAST)

!$OMP WORKSHARE
      CC = AA * BB
      DD = AA + BB
      FIRST = CC(1,1) + DD(1,1)
      LAST = CC(N,N) + DD(N,N)
!$OMP END WORKSHARE NOWAIT

!$OMP END PARALLEL
 
      END