10.3.2 OpenMP Parallelization Directives

OpenMP is a parallel programming model for multi-processor platforms that is becoming standard programming practice for Fortran 95, C, and C++ applications. It is the preferred parallel programming model for Sun Studio compilers.

To enable OpenMP directives, compile with the -openmp option flag. Fortran 95 OpenMP directives are identified with the comment-like sentinel !$OMP followed by the directive name and subordinate clauses.

The !$OMP PARALLEL directive identifies the parallel regions in a program. The !$OMP DO directive identifies DO loops within a parallel region that are to be parallelized. These directives can be combined into a single !$OMP PARALLEL DO directive that must be placed immediately before the DO loop.

The OpenMP specification includes a number of directives for sharing and synchronizing work in a parallel region of a program, and subordinate clauses for data scoping and control.

One major difference between OpenMP and legacy Sun-style directives is that OpenMP requires explicit data scoping as either private or shared, but and automatic scoping feature is provided.

For more information, including guidelines for converting legacy programs using Sun and Cray parallelization directives, see the OpenMP API User’s Guide.