Overview

The major CPU vendors are shifting gears, choosing to add parallelism support on-chip with multi-core processors in order to avoid many of the technological hurdles in boosting speeds, while still offering a better performing processor. However, if your software does not take advantage of these multiple cores, it may not run any faster. That is where OpenMP plays a key role by providing an easy method for threading applications without burdening the programmer with the complications of creating, synchronizing, load balancing, and destroying threads.

The OpenMP standard was formulated in 1997 as an API for writing portable, multithreaded applications. It started as a Fortran-based standard, but later grew to include C and C++. The current version is OpenMP Version 2.5, which supports Fortran, C, and C++. Intel C++ and Fortran compilers support the OpenMP Version 2.5 standard (www.openmp.org). The OpenMP programming model provides a platform-independent set of compiler pragmas, directives, function calls, and environment variables that explicitly instruct the compiler how and where to use parallelism in the application. Many loops can be threaded by inserting only one pragma right before the loop, as demonstrated by examples in this chapter. By leaving the nitty-gritty details to the compiler and OpenMP runtime library, you can spend more time determining which loops should be threaded and how to best restructure the algorithms for performance on multi-core processors. The full potential of OpenMP is realized when it is used to thread the most time-consuming loops, that is, the hot spots.