KokkosTutorial04

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//                             Kokkos
//         Manycore Performance-Portable Multidimensional Arrays
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#include <Kokkos_Core.hpp>
#include <cstdio>

// The type of a two-dimensional N x 3 array of double.
// It lives in Kokkos' default memory space.
typedef Kokkos::View<double*[3]> view_type;

// The "HostMirror" type corresponding to view_type above is also a
// two-dimensional N x 3 array of double.  However, it lives in the
// host memory space corresponding to view_type's memory space.  For
// example, if view_type lives in CUDA device memory, host_view_type
// lives in host (CPU) memory.  Furthermore, declaring host_view_type
// as the host mirror of view_type means that host_view_type has the
// same layout as view_type.  This makes it easier to copy between the
// two Views.
// Advanced issues: If a memory space is accessible from the host without
// performance penalties then it is its own host_mirror_space. This is
// the case for HostSpace, CudaUVMSpace and CudaHostPinnedSpace.

typedef view_type::HostMirror host_view_type;

struct ReduceFunctor {
  view_type a;
  ReduceFunctor (view_type a_) : a (a_) {}
  typedef int value_type; //Specify type for reduction value, lsum

  KOKKOS_INLINE_FUNCTION
  void operator() (int i, int &lsum) const {
    lsum += a(i,0)-a(i,1)+a(i,2);
  }
};

int main() {
  Kokkos::initialize();

  view_type a ("A", 10);
  // If view_type and host_mirror_type live in the same memory space,
  // a "mirror view" is just an alias, and deep_copy does nothing.
  // Otherwise, a mirror view of a device View lives in host memory,
  // and deep_copy does a deep copy.
  host_view_type h_a = Kokkos::create_mirror_view (a);

  // The View h_a lives in host (CPU) memory, so it's legal to fill
  // the view sequentially using ordinary code, like this.
  for (int i = 0; i < 10; i++) {
    for (int j = 0; j < 3; j++) {
      h_a(i,j) = i*10 + j;
    }
  }
  Kokkos::deep_copy (a, h_a); // Copy from host to device.

  int sum = 0;
  Kokkos::parallel_reduce (10, ReduceFunctor (a), sum);
  printf ("Result is %i\n",sum);

  Kokkos::finalize ();
}