Run STL algorithms in parallel with execution policies

Beginning with C++17, many of the standard STL algorithms can run with parallel execution. This feature allows an algorithm to split its work into sub-tasks to run simultaneously on multiple cores. These algorithms accept an execution policy object that specifies the kind of parallelism applied to the algorithm. This feature requires hardware support.

How to do it…

Execution policies are defined in the <execution> header and in the std::execution namespace. In this recipe, we will test the available policies using the std::transform() algorithm:

• For timing purposes, we'll use the duration object with the std::milli ratio so that we can measure in milliseconds:

  using dur_t = duration<double, std::milli>;

• For demonstration purposes, we'll start with a vector of int with 10 million random values:

  int main() {
      std::vector<unsigned> v(10 * 1000 * 1000);
   ...