From b169b9bace81d3a1e0428474e4f9444626156298 Mon Sep 17 00:00:00 2001
From: Bruno Turcksin <bruno.turcksin@gmail.com>
Date: Tue, 15 Feb 2022 19:04:09 +0000
Subject: [PATCH] Add support for ArborX::DistributedTree

---
 include/deal.II/arborx/distributed_tree.h | 134 ++++++++++++++++++++++
 1 file changed, 134 insertions(+)
 create mode 100644 include/deal.II/arborx/distributed_tree.h

diff --git a/include/deal.II/arborx/distributed_tree.h b/include/deal.II/arborx/distributed_tree.h
new file mode 100644
index 0000000000..2dba72b548
--- /dev/null
+++ b/include/deal.II/arborx/distributed_tree.h
@@ -0,0 +1,134 @@
+// ---------------------------------------------------------------------
+//
+// Copyright (C) 2022 by the deal.II authors
+//
+// This file is part of the deal.II library.
+//
+// The deal.II library is free software; you can use it, redistribute
+// it, and/or modify it under the terms of the GNU Lesser General
+// Public License as published by the Free Software Foundation; either
+// version 2.1 of the License, or (at your option) any later version.
+// The full text of the license can be found in the file LICENSE.md at
+// the top level directory of deal.II.
+//
+// ---------------------------------------------------------------------
+
+#ifndef dealii_arborx_distributed_tree_h
+#define dealii_arborx_distributed_tree_h
+
+#include <deal.II/base/config.h>
+
+#if defined(DEAL_II_ARBORX_WITH_MPI) && defined(DEAL_II_WITH_MPI)
+#  include <deal.II/arborx/access_traits.h>
+
+#  include <ArborX_DistributedTree.hpp>
+#  include <Kokkos_Core.hpp>
+
+DEAL_II_NAMESPACE_OPEN
+
+namespace ArborXWrappers
+{
+  /**
+   * This class implements a wrapper around ArborX::DistributedTree, the
+   * distributed version of ArborX:BVH.
+   *
+   * Because ArborX uses Kokkos, Kokkos needs to be initialized and finalized
+   * before using this class.
+   */
+  class DistributedTree
+  {
+  public:
+    /**
+     * Constructor. Use a vector of BoundingBox @p bounding_boxes as primitives.
+     * The BoundingBox objects in @p bounding_boxes are local to the MPI process.
+     */
+    template <int dim, typename Number>
+    DistributedTree(
+      const MPI_Comm &                             comm,
+      const std::vector<BoundingBox<dim, Number>> &bounding_boxes);
+
+    /**
+     * Constructor. Use a vector of @p points as primitives. The Point objects
+     * in @p points are local to the MPI process.
+     */
+    template <int dim, typename Number>
+    DistributedTree(const MPI_Comm &                       comm,
+                    const std::vector<Point<dim, Number>> &points);
+
+    /**
+     * Return the indices and the MPI ranks of those BoundingBox objects that
+     * satisfy the @p queries.
+     * Because @p queries can contain multiple queries, the function returns a pair
+     * of indices and ranks and the associated offsets.
+     *
+     * Valid `QueryType` classes are
+     * ArborXWrappers::BoundingBoxIntersectPredicate,
+     * ArborXWrappers::BoundingBoxNearestPredicate,
+     * ArborXWrappers::PointIntersectPredicate, and
+     * ArborXWrappers::PointNearestPredicate,
+     */
+    template <typename QueryType>
+    std::pair<std::vector<std::pair<int, int>>, std::vector<int>>
+    query(const QueryType &queries);
+
+  private:
+    /**
+     * Underlying ArborX object.
+     */
+    ArborX::DistributedTree<Kokkos::HostSpace> distributed_tree;
+  };
+
+
+
+  template <int dim, typename Number>
+  DistributedTree::DistributedTree(
+    const MPI_Comm &                             comm,
+    const std::vector<BoundingBox<dim, Number>> &bounding_boxes)
+    : distributed_tree(comm,
+                       Kokkos::DefaultHostExecutionSpace{},
+                       bounding_boxes)
+  {}
+
+
+
+  template <int dim, typename Number>
+  DistributedTree::DistributedTree(
+    const MPI_Comm &                       comm,
+    const std::vector<Point<dim, Number>> &points)
+    : distributed_tree(comm, Kokkos::DefaultHostExecutionSpace{}, points)
+  {}
+
+
+
+  template <typename QueryType>
+  std::pair<std::vector<std::pair<int, int>>, std::vector<int>>
+  DistributedTree::query(const QueryType &queries)
+  {
+    Kokkos::View<int *, Kokkos::HostSpace> offsets("offsets", 0);
+    Kokkos::View<Kokkos::pair<int, int> *, Kokkos::HostSpace> indices_ranks(
+      "indices_ranks", 0);
+    distributed_tree.query(Kokkos::DefaultHostExecutionSpace{},
+                           queries,
+                           indices_ranks,
+                           offsets);
+
+    std::vector<std::pair<int, int>> indices_ranks_vector;
+    for (unsigned int i = 0; i < indices_ranks.extent(0); ++i)
+      {
+        indices_ranks_vector.emplace_back(indices_ranks(i).first,
+                                          indices_ranks(i).second);
+      }
+
+    std::vector<int> offsets_vector;
+    offsets_vector.insert(offsets_vector.begin(),
+                          offsets.data(),
+                          offsets.data() + offsets.extent(0));
+
+    return {indices_ranks_vector, offsets_vector};
+  }
+} // namespace ArborXWrappers
+
+DEAL_II_NAMESPACE_CLOSE
+
+#endif
+#endif
-- 
2.39.5