OpenMP race conditions with conditional statement - c++

Question

I'm trying to parallelize a piece of code, I've solved the problem of dispatching in parallel the insertions in a map with a reduction. But the program gives me a memory error I think related to the conditional check on the map size. There is a conceptual error or is it possible to synchronize also that part?
if (PERF_ROWS == MAX_ROWS)
{
int array_dist[PERF_ROWS];
#pragma omp declare reduction (merge : std::multimap<float, int> : omp_out.insert(omp_in.begin(),omp_in.end()))
#pragma omp parallel for schedule(dynamic) reduction(merge: ranking_map) private(array_dist)
for (int i = 0; i < MAX_COLUMNS; i++)
{
if (i % PERF_CLMN == 1) continue;
for (int j = 0; j < PERF_ROWS; j++)
{
array_dist[j] = abs(input[j] - input_matrix[j][i]);
}
float av = mean(PERF_ROWS, array_dist);
float score = score_func(av);
//cout<<score<<" "<<av<<endl;
//#pragma omp critical(rank_func)
//rank_function(score, i);
multimap<float,int>::iterator it = ranking_map.begin();
if (ranking_map.size() < NUM_RES)
{
ranking_map.insert({score, i});
}
else if (score > it -> first)
{
ranking_map.erase(it);
ranking_map.insert({score, i});
}
}

Answer 1

Well, define your own combiner.
Make a function called insertwhatever and write something like this:
void insertwhatever(std::multimap<float, int>& a, std::multimap<float, int>&b)
{
for(auto iterb : b)
{
if(a.size() < NUM_RES)
{
a.insert(iterb);
}
else if(....)
{
(dont know what you want to do here)
}
}
}
Then change the reduction in
#pragma omp declare reduction (merge : std::multimap<float, int> : insertwhatever(omp_out,omp_in))
I am not perfectly sure but i think this should work. Still i don't really understand what exeactly you are trying to do.