Basic OpenMP functions

There are 3 basic functions in OpenMP namely omp_get_thread_num, omp_set_num_threads (nthreads) and omp_get_num_threads.

Functions

• omp_get_thread_num() - get the thread rank in a parallel region (0- omp_get_num_threads() -1)
• omp_set_num_threads(nthreads) - set the number of threads used in a parallel region
• omp_get_num_threads() - get the number of threads used in a parallel region

Example

#include <omp.h>
int omp_get_thread_num();
# pragma omp parallel
{
  printf("Thread rank: %d\n", omp_get_thread_num());
}

Output

Note that the thread rank is not in order:

Thread rank:  2
Thread rank:  0
Thread rank:  3
Thread rank:  1