OpenMP (Open Multi-Processing) is an application programming interface (API) that supports multi-platform shared memory multiprocessing programming in C/C++ and Fortran on many architectures, including Unix and Microsoft Windows platforms. It consists of a set of compiler directives, library routines, and environment variables that influence run-time behavior.
GNU Fortran strives to be compatible to the OpenMP Application Program Interface v4.0.
To enable the processing of the OpenMP directive
free-form source code; the
directives in fixed form; the
!$ conditional compilation sentinels
in free form; and the
in fixed form, gfortran needs to be invoked with the
-fopenmp. This also arranges for automatic linking of the
GNU OpenMP runtime library libgomp.
The OpenMP Fortran runtime library routines are provided both in a
form of a Fortran 90 module named
omp_lib and in a form of
include file named omp_lib.h.
An example of a parallelized loop taken from Appendix A.1 of the OpenMP Application Program Interface v2.5:
SUBROUTINE A1(N, A, B) INTEGER I, N REAL B(N), A(N) !$OMP PARALLEL DO !I is private by default DO I=2,N B(I) = (A(I) + A(I-1)) / 2.0 ENDDO !$OMP END PARALLEL DO END SUBROUTINE A1