Question

I am trying to use OpenMP for threading as it is cross platform. However I can’t work out how to make the code after the parallel continue while the loop is running? It basically just executes the first loop in parallel but never gets to the second non parallel loop?

int main() {
    #pragma omp parallel 
        while(1) {
            Sleep(4000);
            printf("doing work in thread %d, nthreads %d\n", omp_get_thread_num(), omp_get_num_threads());
        }


    while (1) {
        Sleep(4000);
        printf("Hello from main %d, nthreads %d\n", omp_get_thread_num(), omp_get_num_threads());
    }
}

Answer 1

I think you could just make one of the threads your special thread within your omp parallel block

int main() {
    #pragma omp parallel 
        if(omp_get_thread_num()==0){
             while(1) {
                Sleep(4000);
               printf("Hello from main %d, nthreads %d\n", omp_get_thread_num(), omp_get_num_threads());
             }
        }else{
             while(1) {
                Sleep(4000);
                printf("doing work in thread %d, nthreads %d\n", omp_get_thread_num(), omp_get_num_threads());
             }
         }
    }
}

Weather this makes sense in your case is hard to judge without more details.

You could also use sections. Example from here: http://bisqwit.iki.fi/story/howto/openmp/#Sections :

#pragma omp parallel // starts a new team
{
   //Work0(); // this function would be run by all threads.

   #pragma omp sections // divides the team into sections
   { 
     // everything herein is run only once.
     { Work1(); }
     #pragma omp section
     { Work2();
       Work3(); }
     #pragma omp section
     { Work4(); }
   }

   //Work5(); // this function would be run by all threads.
}

You can do nested renationalisation: OpenMP: What is the benefit of nesting parallelizations?