Parallel Programming in Fortran 95 using OpenMP - People

2 1. OpenMP Fortran Application Program Interface
1.1.1 Historical remarks
Shared-memory machines exist nowadays for a long time. In the past, each vendor was developing
its own ”standard” of compiler directives and libraries, which allowed a program
to make use of the capabilities of their specific parallel machine.
An earlier standardization effort, ANSI X3H5 was never formally adopted, since on one
hand no strong support of the vendors was existing and on the other hand distributed
memory machines, with their own more standard message passing libraries PVM and
MPI, appeared as a good alternative to shared-memory machines.
But in 1996-1997, a new interest in a standard shared-memory programming interface
appeared, mainly due to:
1. A renewed interest from the vendors side in shared-memory architectures.
2. The opinion by a part of the vendors, that the parallelization of programs using
message passing interfaces is cumbersome and long and that a more abstract programming
interface would be desirable.
OpenMP 1 is the result of a large agreement between hardware vendors and compiler
developers and is considered to be an ”industry standard”: it specifies a set of compiler
directives, library routines, and environment variables that can be used to specify sharedmemory
parallelism in Fortran and C/C++ programs.
OpenMP consolidates all this into a single syntax and semantics and finally delivers
the long-awaited promise of single source portability for shared-memory parallelism. But
OpenMP is even more: it also addresses the inability of previous shared-memory directive
sets to deal with coarse-grain parallelism 2 . In the past, limited support for coarse
grain work has led to developers to think that shared-memory parallel programming was
inherently limited to fine-grain parallelism 3 .
1.1.2 Who is participating
The OpenMP specification is owned, written and maintained by the OpenMP Architecture
Review Board, which is a join of the companies actively taking part in the
development of the standard shared-memory programming interface. In the year 2000,
the permanent members of the OpenMP ARB were:
• US Department of Energy, through its ASCI program
• Compaq Computer Corp.
1 MP stands for Multi Processing and Open means that the standard is defined through a specification
accessible to anyone.
2 Coarse-grain parallelism means that the parallelism in the program is achieved through a decomposition
of the target domain into a set of subdomains that is distributed over the different processors of
the machine.
3 Fine-grain parallelism means that the parallelism in the program is achieved by distributing the
work of the do-loops over the different processors, so that each processor computes part of the iterations.