使用openmp编程-杨全胜.ppt

* Introduce OpenMP by stating that OpenMP, Open specifications for Multi Processing, is an application programming interface (API) that was formulated in 1997. It is used for writing portable, multithreaded applications. OpenMP has made it easy to create threaded Fortran and C/C++ programs. Unlike Windows threads, OpenMP does not require you to create, synchronize, load balance, and destroy threads. OpenMP is not formally accepted as an industry standard for programming, but it is used widely. OpenMP provides a set of compiler directives—instructions embedded in source code—that informs compilers about the intent of compilation. Compiler directives tell the compiler how to compile. For example, the #include stdio.h compiler directive informs the compiler to include the stdio.h file and compile the code using the contents of this header file. Earlier, shared-memory platform vendors had their own sets of compiler directives to implement shared-memory parallelism. OpenMP standardizes almost 20 years of compiler-directed threading experience by combining common functionality from various vendors into a portable API. OpenMP provides a special syntax that programmers can use to create multithreaded code. It enables you to combine serial and parallel code in a single source. If your compiler does not recognize OpenMP directives, the compiler ignores the directives and the code enclosed within the directive. Such a situation yields a serial executable code. OpenMP also supports incremental parallelism. Incremental parallelism allows you to first thread one segment of the code and tests it for better performance. You can then successively modify and test other code segments. This helps you give priority to threading critical problems in a code segment. If threading results in worse performance, you can remove the new OpenMP directives and proceed to the next code segment. OpenMP also supports both coarse-grain and fine-grain parallelism. OpenMP also supports and stan