Function OptionalParallelFor

cpp/src/arrow/util/parallel.h:70–80

template <class FUNCTION>
Status OptionalParallelFor(bool use_threads, int num_tasks, FUNCTION&& func,
                           Executor* executor = internal::GetCpuThreadPool()) {
  if (use_threads) {
    return ParallelFor(num_tasks, std::forward<FUNCTION>(func), executor);
  } else {
    for (int i = 0; i < num_tasks; ++i) {
      RETURN_NOT_OK(func(i));
    }
    return Status::OK();
  }
}

// A parallelizer that takes a `Result<R>(int index, T item)` function and
// calls it with each item from the input array, in sequence or in parallel,