#C

Copy this into loops.c

#include <stdio.h>

#ifdef _OPENMP
    #include <omp.h>
#else
    #define omp_get_thread_num() 0
#endif

int main(int argc, char **argv)
{
    int i, thread_id, nloops;

    #pragma omp parallel private(thread_id, nloops)
    {
        nloops = 0;

        #pragma omp for
        for (i=0; i<1000; ++i)
        {
            ++nloops;
        }

        thread_id = omp_get_thread_num();

        printf("Thread %d performed %d iterations of the loop.\n",
                thread_id, nloops );
    }

    return 0;
}

The new directive in this code is omp for. This tells the compiler that the for loop directly below this pragma can be run in parallel by the team of threads. In this case, the only work performed in each iteration is increasing the thread private counter of the number of times that the loop has been performed (each thread in the team has its own copy of nloops because it is specified as private as part of the OpenMP parallel pragma). By doing this, each thread in the team counts up the number of times that it has performed the loop.

You can compile this program using one of these commands (choose one for the compiler you wish to use);

• gcc : gcc -fopenmp loops.c -o loops
• icc : icc -openmp loops.c -o loops -cxxlib-icc
• pgc : pgc -mp loops.c -o loops

This will produce the executable, loops.

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