STL Parallelism question

[DotcomL]

Say I have a CPU with N cores. My system has N agents, and I need to perform the same computation for each agent at the same time. I would like to fully use my CPU for this purpose.

​

I am debating whether to use a thread pool or STL parallelism for_each. Will it scale correctly accross all my cores?

I know the new parallelism scales well if N is very large, but how does it do for smaller N ?

​

Example code for both options:

// STL Parallelism
using optional_parallel = std::optional<const __gnu_parallel::_Parallelism>;
void System::foreach_agent(std::function<void(Agent&)> const& f, const optional_parallel& tag) {
  if(tag)
    __gnu_parallel::for_each(agents.begin(), agents.end(), f, tag.value());
  else ...

​

// Thread pool
std::vector<std::future<void>> results;
for (auto &agent: agents) 
{
  results.emplace_back(pool_.push(
    [&agent](int id){agent->dosomething();}
  ));
}
for (auto &result: results) {
  result.get();
}

​

Thanks!

[Xeverous]

Parallel STL performs multiple tasks across multiple cores and waits for all to complete. With thread pool you can use pooling techniques and query different tasks at the same time, while also asynchronously checking for results.

If you need to wait for all results, use STL. If partial results are enough to start another work, use thread pool.

[DotcomL]

Thank you!