Why is OpenMP outperforming threads?

Question

I\'ve been calling this in OpenMP

#pragma omp parallel for num_threads(totalThreads)
for(unsigned i=0; i

        

Answer 1

Where does totalThreads come from in your OpenMP version? I bet it's not startIndex.size().

The OpenMP version queues the requests onto totalThreads worker threads. It looks like the C++11 version creates, startIndex.size() threads, which involves a ridiculous amount of overhead if that's a big number.