 use the result of std::thread::hardware_concurrency()
            </p>
<p>
              This algorithm uses a <span class="bold"><strong>comparison object</strong></span>,
              in the same way as the standard library sort algorithms. If not defined,
              the comparison object is std::less, which uses the &lt; operator internally.
            </p>
<p>
              This algorithm is <span class="bold"><strong>exception safe</strong></span>,
              meaning that, the exceptions gener