OpenMP while loop

Question

I have a code that runs many iterations and only if a condition is met, the result of the iteration is saved. This is naturally expressed as a while loop. I am attempting to

Answer 1

You can basically follow the same concept as for this question, with a slight variation to ensure that avRes is not written to in parallel:

int nit = 0;
#pragma omp parallel
while(1) {
     int local_nit;
     #pragma omp atomic read
     local_nit = nit;
     if (local_nit >= avit) {
          break;
     }

     [...]

     if (...) { 
          #pragma omp critical
          {
                #pragma omp atomic capture
                local_nit = ++nit;
                for(j=0;j<jmax;j++){
                    avRes[j] += Res[j];
                } 
                for(j=0;j<jmax;j++){
                    // technically you could also use `nit` directly since
                    // now `nit` is only modified within this critical section
                    cout<<avRes[j]/local_nit<<"\t";
                }
          }
     } else {
          #pragma omp atomic update
          dit++;
     }
 }

It also works with critical regions, but atomics are more efficient.

There's another thing you need to consider, rand() should not be used in parallel contexts. See this question. For C++, use a private (i.e. defined within the parallel region) random number generator from <random>.