title: Why to use OpenMP Single inside of OpenMP parallel block?
body: <p>For example:</p>
  
  <pre><code>#pragma omp parallel num_threads(2)
  {
      #pragma omp single
      QuickSort(arr, 0, arr.length, cuttoff);
  }
  </code></pre>
  
  <p>As far as i know <code>#pragma omp single</code> makes code serial. Only one process will will execute QuickSort(). Is something wrong with the upper code?</p>