OpenMP, for loop inside section

Question

I would like to run the following code (below). I want to spawn two independent threads, each one would run a parallel for loop. Unfortunately, I get an error. Apparently, p

Answer 1

Here you have to use nested parallelism. The problem with the omp for in the sections is that all the threads in scope have to take part in the omp for, and they clearly don't — they're broken up by sections. So you have to introduce functions, and do nested paralleism within the functions.

#include 
#include 

void doTask1(const int gtid) {
    omp_set_num_threads(5);
#pragma omp parallel 
    {
        int tid = omp_get_thread_num();
        #pragma omp for
        for(int i=0; i<5; i++) {
            printf("x %d %d %d\n", i, tid, gtid);
        }
    }
}

void doTask2(const int gtid) {
    omp_set_num_threads(5);
#pragma omp parallel 
    {
        int tid = omp_get_thread_num();
        #pragma omp for
        for(int i=0; i<5; i++) {
            printf(". %d %d %d\n", i, tid, gtid);
        }
    }
}


int main()
{
    omp_set_num_threads(2);
    omp_set_nested(1);

#pragma omp parallel    
    {
        int gtid = omp_get_thread_num();
#pragma omp sections
        {
#pragma omp section
            doTask1(gtid);

#pragma omp section
            doTask2(gtid);
        } // end parallel and end sections
    }
}