OpenMP status tests

README.md

OpenMP status tests

These tests show 3 different outcomes of the OpenMP C code execution:

1. OpenMP is not enabled in the compiler: this situation can be detected by checking whether the _OPENMP macro is defined or not
2. OpenMP is enabled and deployed at full scale: the master thread in an OpenMP parallel region checks the omp_get_num_threads() value, and the system-default number of available hardware threads is returned
3. OpenMP is enabled, but the parallelism is limited to 1 thread, by user's choice

Testing

►make
gcc openmp_check_enabled.c -o test1 && ./test1
OpenMP is not enabled in compile time!
gcc -fopenmp openmp_check_enabled.c -o test2 && ./test2
nthreads = 8
gcc -fopenmp openmp_check_enabled.c -o test3 && OMP_NUM_THREADS=1 ./test3
nthreads = 1
warning: only one thread is deployed!

Makefile

all: test1 test2 test3

test1: openmp_check_enabled.c
	gcc $< -o $@ && ./test1

test2: openmp_check_enabled.c
	gcc -fopenmp $< -o $@ && ./test2

test3: openmp_check_enabled.c
	gcc -fopenmp $< -o $@ && OMP_NUM_THREADS=1 ./test3

clean:
	rm -rf test1 test2 test3

openmp_check_enabled.c

#include <omp.h>
#include <stdio.h>

int main()
{
#ifdef _OPENMP // automatically defined if OpenMP is enabled during compile-time
    #pragma omp parallel
    {
        #pragma omp master
        {
            int nthreads = omp_get_num_threads();
            printf("nthreads = %d\n", nthreads);
            if (nthreads == 1)
                printf("warning: only one thread is deployed!");
        }
    }
#else
    printf("OpenMP is not enabled in compile time!\n");
#endif
    return 0;

}