title: Is it possible to limit threads count for C++ 17 parallel `for_each`?
body: <p>I use <code>std::for_each</code> with <code>std::execution::par</code> to perform complex computation on huge input represented as vector of structures. The computation doesn't need any delays related to hardware (network or disk IO for example), it is "just CPU" computation. For me it looks logical that there are no sense to create more OS threads that we have hardware ones; however, Visual C++ 2019 creates in average 50 threads, and sometimes up to 500 ones even there are only 12 hardware threads.</p>
  
  <p>Is there a way to limit parallel threads count to <code>hardware_concurrency</code> with <code>std::for_each</code> and <code>std::execution::par</code>, or the only way to create reasonable threads count is to use custom code with <code>std::thread</code>?</p>