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What is OpenMP?
OpenMP is a set of compiler directives as well as an API for programs written in C, C++, or FORTRAN that provides support for parallel programming in shared-memory environments. OpenMP identifies parallel regions as blocks of code that may run in parallel. Application developers insert compiler directives into their code at parallel regions, and these directives instruct the OpenMP run-time library to execute the region in parallel. The following C program illustrates a compiler directive above the parallel region containing the printf() statement −
#include <omp.h>
#include <stdio.h>
int main(int argc, char *argv[]){
/* sequential code */
#pragma omp parallel{
printf("I am a parallel region.");
}
/* sequential code */
return 0;
}When OpenMP encounters the directive
#pragma omp parallel
It creates as many threads which are processing cores in the system. Thus, for a dual-core system, two threads are created, for a quad-core system, four are created; and so forth. Then all the threads simultaneously execute the parallel region. When each thread exits the parallel region, it is terminated. OpenMP provides several additional directives for running code regions in parallel, including parallelizing loops.
In addition to providing directives for parallelization, OpenMP allows developers to choose among several levels of parallelism. E.g., they can set the number of threads manually. It also allows developers to identify whether data are shared between threads or are private to a thread. OpenMP is available on several open-source and commercial compilers for Linux, Windows, and Mac OS X systems.
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