Tpetra_Details_packCrsGraph_def.hpp

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// @HEADER
// *****************************************************************************
//          Tpetra: Templated Linear Algebra Services Package
//
// Copyright 2008 NTESS and the Tpetra contributors.
// SPDX-License-Identifier: BSD-3-Clause
// *****************************************************************************
// @HEADER
 
#ifndef TPETRA_DETAILS_PACKCRSGRAPH_DEF_HPP
#define TPETRA_DETAILS_PACKCRSGRAPH_DEF_HPP
 
#include "TpetraCore_config.h"
#include "Teuchos_Array.hpp"
#include "Teuchos_ArrayView.hpp"
#include "Tpetra_Details_Behavior.hpp"
#include "Tpetra_Details_castAwayConstDualView.hpp"
#include "Tpetra_Details_createMirrorView.hpp"
#include "Tpetra_Details_getEntryOnHost.hpp"
#include "Tpetra_Details_OrdinalTraits.hpp"
#include "Tpetra_Details_PackTraits.hpp"
#include "Tpetra_CrsGraph_decl.hpp"
#include <memory>
#include <string>
 
 
namespace Tpetra {
 
//
// Users must never rely on anything in the Details namespace.
//
namespace Details {
 
namespace PackCrsGraphImpl {
template <class OutputOffsetsViewType,
          class CountsViewType,
          class InputOffsetsViewType,
          class InputLocalRowIndicesViewType,
          class InputLocalRowPidsViewType,
          const bool debug =
#ifdef HAVE_TPETRA_DEBUG
              true
#else
              false
#endif  // HAVE_TPETRA_DEBUG
          >
class NumPacketsAndOffsetsFunctor {
 public:
  typedef typename OutputOffsetsViewType::non_const_value_type output_offset_type;
  typedef typename CountsViewType::non_const_value_type count_type;
  typedef typename InputOffsetsViewType::non_const_value_type input_offset_type;
  typedef typename InputLocalRowIndicesViewType::non_const_value_type local_row_index_type;
  typedef typename InputLocalRowPidsViewType::non_const_value_type local_row_pid_type;
  // output Views drive where execution happens.
  typedef typename OutputOffsetsViewType::device_type device_type;
  static_assert(std::is_same<typename CountsViewType::device_type::execution_space,
                             typename device_type::execution_space>::value,
                "OutputOffsetsViewType and CountsViewType must have the same execution space.");
  static_assert(Kokkos::is_view<OutputOffsetsViewType>::value,
                "OutputOffsetsViewType must be a Kokkos::View.");
  static_assert(std::is_same<typename OutputOffsetsViewType::value_type, output_offset_type>::value,
                "OutputOffsetsViewType must be a nonconst Kokkos::View.");
  static_assert(std::is_integral<output_offset_type>::value,
                "The type of each entry of OutputOffsetsViewType must be a built-in integer type.");
  static_assert(Kokkos::is_view<CountsViewType>::value,
                "CountsViewType must be a Kokkos::View.");
  static_assert(std::is_same<typename CountsViewType::value_type, output_offset_type>::value,
                "CountsViewType must be a nonconst Kokkos::View.");
  static_assert(std::is_integral<count_type>::value,
                "The type of each entry of CountsViewType must be a built-in integer type.");
  static_assert(Kokkos::is_view<InputOffsetsViewType>::value,
                "InputOffsetsViewType must be a Kokkos::View.");
  static_assert(std::is_integral<input_offset_type>::value,
                "The type of each entry of InputOffsetsViewType must be a built-in integer type.");
  static_assert(Kokkos::is_view<InputLocalRowIndicesViewType>::value,
                "InputLocalRowIndicesViewType must be a Kokkos::View.");
  static_assert(std::is_integral<local_row_index_type>::value,
                "The type of each entry of InputLocalRowIndicesViewType must be a built-in integer type.");
 
  NumPacketsAndOffsetsFunctor(const OutputOffsetsViewType& outputOffsets,
                              const CountsViewType& counts,
                              const InputOffsetsViewType& rowOffsets,
                              const InputLocalRowIndicesViewType& lclRowInds,
                              const InputLocalRowPidsViewType& lclRowPids)
    : outputOffsets_(outputOffsets)
    , counts_(counts)
    , rowOffsets_(rowOffsets)
    , lclRowInds_(lclRowInds)
    , lclRowPids_(lclRowPids)
    , error_("error")  // don't forget this, or you'll get segfaults!
  {
    if (debug) {
      const size_t numRowsToPack = static_cast<size_t>(lclRowInds_.extent(0));
 
      if (numRowsToPack != static_cast<size_t>(counts_.extent(0))) {
        std::ostringstream os;
        os << "lclRowInds.extent(0) = " << numRowsToPack
           << " != counts.extent(0) = " << counts_.extent(0)
           << ".";
        TEUCHOS_TEST_FOR_EXCEPTION(true, std::invalid_argument, os.str());
      }
      if (static_cast<size_t>(numRowsToPack + 1) !=
          static_cast<size_t>(outputOffsets_.extent(0))) {
        std::ostringstream os;
        os << "lclRowInds.extent(0) + 1 = " << (numRowsToPack + 1)
           << " != outputOffsets.extent(0) = " << outputOffsets_.extent(0)
           << ".";
        TEUCHOS_TEST_FOR_EXCEPTION(true, std::invalid_argument, os.str());
      }
    }
  }
 
  KOKKOS_INLINE_FUNCTION void
  operator()(const local_row_index_type& curInd,
             output_offset_type& update,
             const bool final) const {
    if (debug) {
      if (curInd < static_cast<local_row_index_type>(0)) {
        error_() = 1;
        return;
      }
    }
 
    if (final) {
      if (debug) {
        if (curInd >= static_cast<local_row_index_type>(outputOffsets_.extent(0))) {
          error_() = 2;
          return;
        }
      }
      outputOffsets_(curInd) = update;
    }
 
    if (curInd < static_cast<local_row_index_type>(counts_.extent(0))) {
      const auto lclRow = lclRowInds_(curInd);
      if (static_cast<size_t>(lclRow + 1) >= static_cast<size_t>(rowOffsets_.extent(0)) ||
          static_cast<local_row_index_type>(lclRow) < static_cast<local_row_index_type>(0)) {
        error_() = 3;
        return;
      }
      // count_type could differ from the type of each row offset.
      // For example, row offsets might each be 64 bits, but if their
      // difference always fits in 32 bits, we may then safely use a
      // 32-bit count_type.
      const count_type count =
          static_cast<count_type>(rowOffsets_(lclRow + 1) - rowOffsets_(lclRow));
 
      // We pack first the global column indices and then pids (if any),
      // However, if the number of entries in the row is zero, we pack nothing.
      const count_type numEntToPack = (count == 0)
                                          ? static_cast<count_type>(0)
                                          : count * (1 + (lclRowPids_.size() > 0 ? 1 : 0));
 
      if (final) {
        counts_(curInd) = numEntToPack;
      }
      update += numEntToPack;
    }
  }
 
  // mfh 31 May 2017: Don't need init or join.  If you have join, MUST
  // have join both with and without volatile!  Otherwise intrawarp
  // joins are really slow on GPUs.
 
  int getError() const {
    auto error_h = Kokkos::create_mirror_view(error_);
    // DEEP_COPY REVIEW - DEVICE-TO-HOSTMIRROR
    // Note: In the UVM case, this would otherwise be a no-op
    // and thus not fence, so the value might not be correct on return
    // In the non-UVM case, create_mirror_view will block for the allocation
    Kokkos::deep_copy(error_h, error_);
 
    return error_h();
  }
 
 private:
  OutputOffsetsViewType outputOffsets_;
  CountsViewType counts_;
  typename InputOffsetsViewType::const_type rowOffsets_;
  typename InputLocalRowIndicesViewType::const_type lclRowInds_;
  typename InputLocalRowPidsViewType::const_type lclRowPids_;
  Kokkos::View<int, device_type> error_;
};
 
template <class OutputOffsetsViewType,
          class CountsViewType,
          class InputOffsetsViewType,
          class InputLocalRowIndicesViewType,
          class InputLocalRowPidsViewType>
typename CountsViewType::non_const_value_type
computeNumPacketsAndOffsets(const OutputOffsetsViewType& outputOffsets,
                            const CountsViewType& counts,
                            const InputOffsetsViewType& rowOffsets,
                            const InputLocalRowIndicesViewType& lclRowInds,
                            const InputLocalRowPidsViewType& lclRowPids) {
  typedef NumPacketsAndOffsetsFunctor<OutputOffsetsViewType,
                                      CountsViewType, typename InputOffsetsViewType::const_type,
                                      typename InputLocalRowIndicesViewType::const_type,
                                      typename InputLocalRowPidsViewType::const_type>
      functor_type;
  typedef typename CountsViewType::non_const_value_type count_type;
  typedef typename OutputOffsetsViewType::size_type size_type;
  typedef typename OutputOffsetsViewType::execution_space execution_space;
  typedef typename functor_type::local_row_index_type LO;
  typedef Kokkos::RangePolicy<execution_space, LO> range_type;
  const char prefix[] = "computeNumPacketsAndOffsets: ";
 
  count_type count               = 0;
  const count_type numRowsToPack = lclRowInds.extent(0);
 
  if (numRowsToPack == 0) {
    return count;
  } else {
    TEUCHOS_TEST_FOR_EXCEPTION(rowOffsets.extent(0) <= static_cast<size_type>(1),
                               std::invalid_argument, prefix << "There is at least one row to pack, "
                                                                "but the graph has no rows.  lclRowInds.extent(0) = "
                                                             << numRowsToPack << ", but rowOffsets.extent(0) = " << rowOffsets.extent(0) << " <= 1.");
    TEUCHOS_TEST_FOR_EXCEPTION(outputOffsets.extent(0) !=
                                   static_cast<size_type>(numRowsToPack + 1),
                               std::invalid_argument,
                               prefix << "Output dimension does not match number of rows to pack.  "
                                      << "outputOffsets.extent(0) = " << outputOffsets.extent(0)
                                      << " != lclRowInds.extent(0) + 1 = "
                                      << static_cast<size_type>(numRowsToPack + 1) << ".");
    TEUCHOS_TEST_FOR_EXCEPTION(counts.extent(0) != numRowsToPack, std::invalid_argument,
                               prefix << "counts.extent(0) = " << counts.extent(0)
                                      << " != numRowsToPack = " << numRowsToPack << ".");
 
    functor_type f(outputOffsets, counts, rowOffsets, lclRowInds, lclRowPids);
    Kokkos::parallel_scan("Tpetra::Details::computeNumPacketsAndOffsets::scan", range_type(0, numRowsToPack + 1), f);
 
    // At least in debug mode, this functor checks for errors.
    const int errCode = f.getError();
    TEUCHOS_TEST_FOR_EXCEPTION(errCode != 0, std::runtime_error, prefix << "parallel_scan error code " << errCode << " != 0.");
 
#if 0
    size_t total = 0;
    for (LO k = 0; k < numRowsToPack; ++k) {
      total += counts[k];
    }
    if (outputOffsets(numRowsToPack) != total) {
      if (errStr.get () == NULL) {
        errStr = std::unique_ptr<std::ostringstream> (new std::ostringstream ());
      }
      std::ostringstream& os = *errStr;
      os << prefix
         << "outputOffsets(numRowsToPack=" << numRowsToPack << ") "
         << outputOffsets(numRowsToPack) << " != sum of counts = "
         << total << "." << std::endl;
      if (numRowsToPack != 0) {
        // Only print the array if it's not too long.
        if (numRowsToPack < static_cast<LO> (10)) {
          os << "outputOffsets: [";
          for (LO i = 0; i <= numRowsToPack; ++i) {
            os << outputOffsets(i);
            if (static_cast<LO> (i + 1) <= numRowsToPack) {
              os << ",";
            }
          }
          os << "]" << std::endl;
          os << "counts: [";
          for (LO i = 0; i < numRowsToPack; ++i) {
            os << counts(i);
            if (static_cast<LO> (i + 1) < numRowsToPack) {
              os << ",";
            }
          }
          os << "]" << std::endl;
        }
        else {
          os << "outputOffsets(" << (numRowsToPack-1) << ") = "
             << outputOffsets(numRowsToPack-1) << "." << std::endl;
        }
      }
      count = outputOffsets(numRowsToPack);
      return {false, errStr};
    }
#endif  // HAVE_TPETRA_DEBUG
 
    // Get last entry of outputOffsets, which is the sum of the entries
    // of counts.  Don't assume UVM.
    using Tpetra::Details::getEntryOnHost;
    return static_cast<count_type>(getEntryOnHost(outputOffsets,
                                                  numRowsToPack));
  }
}
 
template <class Packet,
          class LocalMapType,
          class BufferDeviceType,
          class InputLidsType,
          class InputPidsType>
KOKKOS_FUNCTION
    size_t
    packRow(const LocalMapType& col_map,
            const Kokkos::View<Packet*, BufferDeviceType>& exports,
            const InputLidsType& lids_in,
            const InputPidsType& pids_in,
            const size_t offset,
            const size_t num_ent,
            const bool pack_pids) {
  using LO = typename LocalMapType::local_ordinal_type;
  using GO = typename LocalMapType::global_ordinal_type;
 
  if (num_ent == 0) {
    // Empty rows always take zero bytes, to ensure sparsity.
    return static_cast<size_t>(0);
  }
 
  size_t num_ent_packed = num_ent;
  if (pack_pids) {
    num_ent_packed += num_ent;
  }
 
  // Copy column indices one at a time, so that we don't need
  // temporary storage.
  for (size_t k = 0; k < num_ent; ++k) {
    const LO lid        = lids_in[k];
    const GO gid        = col_map.getGlobalElement(lid);
    exports(offset + k) = gid;
  }
  // Copy PIDs one at a time, so that we don't need temporary storage.
  if (pack_pids) {
    for (size_t k = 0; k < num_ent; ++k) {
      const LO lid                  = lids_in[k];
      const int pid                 = pids_in[lid];
      exports(offset + num_ent + k) = static_cast<GO>(pid);
    }
  }
 
  return num_ent_packed;
}
 
template <class Packet,
          class LocalGraph,
          class LocalMap,
          class BufferDeviceType>
struct PackCrsGraphFunctor {
  using local_graph_type = LocalGraph;
  using local_map_type   = LocalMap;
  using LO               = typename local_map_type::local_ordinal_type;
  using GO               = typename local_map_type::global_ordinal_type;
 
  using num_packets_per_lid_view_type =
      Kokkos::View<const size_t*, BufferDeviceType>;
  using offsets_view_type = Kokkos::View<const size_t*, BufferDeviceType>;
  using exports_view_type = Kokkos::View<Packet*, BufferDeviceType>;
  using export_lids_view_type =
      typename PackTraits<LO>::input_array_type;
  using source_pids_view_type =
      typename PackTraits<int>::input_array_type;
 
  using count_type =
      typename num_packets_per_lid_view_type::non_const_value_type;
  using offset_type = typename offsets_view_type::non_const_value_type;
  using value_type  = Kokkos::pair<int, LO>;
 
  static_assert(std::is_same<LO, typename local_graph_type::data_type>::value,
                "local_map_type::local_ordinal_type and "
                "local_graph_type::data_type must be the same.");
 
  local_graph_type local_graph;
  local_map_type local_col_map;
  exports_view_type exports;
  num_packets_per_lid_view_type num_packets_per_lid;
  export_lids_view_type export_lids;
  source_pids_view_type source_pids;
  offsets_view_type offsets;
  bool pack_pids;
 
  PackCrsGraphFunctor(const local_graph_type& local_graph_in,
                      const local_map_type& local_col_map_in,
                      const exports_view_type& exports_in,
                      const num_packets_per_lid_view_type& num_packets_per_lid_in,
                      const export_lids_view_type& export_lids_in,
                      const source_pids_view_type& source_pids_in,
                      const offsets_view_type& offsets_in,
                      const bool pack_pids_in)
    : local_graph(local_graph_in)
    , local_col_map(local_col_map_in)
    , exports(exports_in)
    , num_packets_per_lid(num_packets_per_lid_in)
    , export_lids(export_lids_in)
    , source_pids(source_pids_in)
    , offsets(offsets_in)
    , pack_pids(pack_pids_in) {
    const LO numRows = local_graph_in.numRows();
    const LO rowMapDim =
        static_cast<LO>(local_graph.row_map.extent(0));
    TEUCHOS_TEST_FOR_EXCEPTION(numRows != 0 && rowMapDim != numRows + static_cast<LO>(1),
                               std::logic_error, "local_graph.row_map.extent(0) = " << rowMapDim << " != numRows (= " << numRows << " ) + 1.");
  }
 
  KOKKOS_INLINE_FUNCTION void init(value_type& dst) const {
    using ::Tpetra::Details::OrdinalTraits;
    dst = Kokkos::make_pair(0, OrdinalTraits<LO>::invalid());
  }
 
  KOKKOS_INLINE_FUNCTION void
  join(value_type& dst, const value_type& src) const {
    // `dst` should reflect the first (least) bad index and all other
    // associated error codes and data, so prefer keeping it.
    if (src.first != 0 && dst.first == 0) {
      dst = src;
    }
  }
 
  KOKKOS_INLINE_FUNCTION
  void operator()(const LO i, value_type& dst) const {
    const size_t offset               = offsets[i];
    const LO export_lid               = export_lids[i];
    const size_t buf_size             = exports.size();
    const size_t num_packets_this_lid = num_packets_per_lid(i);
    const size_t num_ent =
        static_cast<size_t>(local_graph.row_map[export_lid + 1] - local_graph.row_map[export_lid]);
 
    // Only pack this row's data if it has a nonzero number of
    // entries.  We can do this because receiving processes get the
    // number of packets, and will know that zero packets means zero
    // entries.
    if (num_ent == 0) {
      return;
    }
 
    if (export_lid >= static_cast<LO>(local_graph.numRows())) {
      if (dst.first != 0) {             // keep only the first error
        dst = Kokkos::make_pair(1, i);  // invalid row
      }
      return;
    } else if ((offset > buf_size || offset + num_packets_this_lid > buf_size)) {
      if (dst.first != 0) {             // keep only the first error
        dst = Kokkos::make_pair(2, i);  // out of bounds
      }
      return;
    }
 
    // We can now pack this row
 
    // Since the graph is locally indexed on the calling process, we
    // have to use its column Map (which it _must_ have in this case)
    // to convert to global indices.
    const auto row_beg = local_graph.row_map[export_lid];
    const auto row_end = local_graph.row_map[export_lid + 1];
    auto lids_in       = Kokkos::subview(local_graph.entries,
                                         Kokkos::make_pair(row_beg, row_end));
    size_t num_ent_packed_this_row =
        packRow(local_col_map, exports, lids_in,
                source_pids, offset, num_ent, pack_pids);
    if (num_ent_packed_this_row != num_packets_this_lid) {
      if (dst.first != 0) {  // keep only the first error
        dst = Kokkos::make_pair(3, i);
      }
    }
  }
};
 
template <class Packet,
          class LocalGraph,
          class LocalMap,
          class BufferDeviceType>
void do_pack(const LocalGraph& local_graph,
             const LocalMap& local_map,
             const Kokkos::View<Packet*, BufferDeviceType>& exports,
             const typename PackTraits<
                 size_t>::input_array_type& num_packets_per_lid,
             const typename PackTraits<
                 typename LocalMap::local_ordinal_type>::input_array_type& export_lids,
             const typename PackTraits<
                 int>::input_array_type& source_pids,
             const Kokkos::View<const size_t*, BufferDeviceType>& offsets,
             const bool pack_pids) {
  using LO              = typename LocalMap::local_ordinal_type;
  using execution_space = typename LocalGraph::device_type::execution_space;
  using range_type      = Kokkos::RangePolicy<execution_space, LO>;
  const char prefix[]   = "Tpetra::Details::PackCrsGraphImpl::do_pack: ";
 
  if (export_lids.extent(0) != 0) {
    TEUCHOS_TEST_FOR_EXCEPTION(static_cast<size_t>(offsets.extent(0)) !=
                                   static_cast<size_t>(export_lids.extent(0) + 1),
                               std::invalid_argument, prefix << "offsets.extent(0) = " << offsets.extent(0) << " != export_lids.extent(0) (= " << export_lids.extent(0) << ") + 1.");
    TEUCHOS_TEST_FOR_EXCEPTION(export_lids.extent(0) != num_packets_per_lid.extent(0),
                               std::invalid_argument, prefix << "export_lids.extent(0) = " << export_lids.extent(0) << " != num_packets_per_lid.extent(0) = " << num_packets_per_lid.extent(0) << ".");
    // If exports has nonzero length at this point, then the graph
    // has at least one entry to pack.  Thus, if packing process
    // ranks, we had better have at least one process rank to pack.
    TEUCHOS_TEST_FOR_EXCEPTION(pack_pids && exports.extent(0) != 0 &&
                                   source_pids.extent(0) == 0,
                               std::invalid_argument, prefix << "pack_pids is true, and exports.extent(0) = " << exports.extent(0) << " != 0, meaning that we need to pack at "
                                                                                                                                      "least one graph entry, but source_pids.extent(0) = 0.");
  }
 
  using pack_functor_type =
      PackCrsGraphFunctor<Packet, LocalGraph, LocalMap,
                          BufferDeviceType>;
  pack_functor_type f(local_graph, local_map, exports,
                      num_packets_per_lid, export_lids,
                      source_pids, offsets, pack_pids);
 
  typename pack_functor_type::value_type result;
  range_type range(0, num_packets_per_lid.extent(0));
  Kokkos::parallel_reduce("Tpetra::Details::computeNumPacketsAndOffsets::reduce", range, f, result);
 
  if (result.first != 0) {
    // We can't deep_copy from AnonymousSpace Views, so we can't
    // print out any information from them in case of error.
    std::ostringstream os;
    if (result.first == 1) {  // invalid local row index
      os << "invalid local row index";
    } else if (result.first == 2) {  // invalid offset
      os << "invalid offset";
    }
    TEUCHOS_TEST_FOR_EXCEPTION(true, std::runtime_error, prefix << "PackCrsGraphFunctor "
                                                                   "reported error code "
                                                                << result.first << " (" << os.str() << ") for the first bad row " << result.second << ".");
  }
}
 
template <typename LO, typename GO, typename NT>
void packCrsGraph(const CrsGraph<LO, GO, NT>& sourceGraph,
                  Kokkos::DualView<
                      typename CrsGraph<LO, GO, NT>::packet_type*,
                      typename CrsGraph<LO, GO, NT>::buffer_device_type>& exports,
                  const Kokkos::View<
                      size_t*,
                      typename CrsGraph<LO, GO, NT>::buffer_device_type>& num_packets_per_lid,
                  const Kokkos::View<
                      const LO*,
                      typename CrsGraph<LO, GO, NT>::buffer_device_type>& export_lids,
                  const Kokkos::View<
                      const int*,
                      typename CrsGraph<LO, GO, NT>::buffer_device_type>& export_pids,
                  size_t& constant_num_packets,
                  const bool pack_pids) {
  using Kokkos::View;
  using crs_graph_type          = CrsGraph<LO, GO, NT>;
  using packet_type             = typename crs_graph_type::packet_type;
  using buffer_device_type      = typename crs_graph_type::buffer_device_type;
  using exports_view_type       = Kokkos::DualView<packet_type*, buffer_device_type>;
  using local_graph_device_type = typename crs_graph_type::local_graph_device_type;
  using local_map_type          = typename Tpetra::Map<LO, GO, NT>::local_map_type;
  const char prefix[]           = "Tpetra::Details::packCrsGraph: ";
  constexpr bool debug          = false;
 
  local_graph_device_type local_graph = sourceGraph.getLocalGraphDevice();
  local_map_type local_col_map        = sourceGraph.getColMap()->getLocalMap();
 
  // Setting this to zero tells the caller to expect a possibly
  // different ("nonconstant") number of packets per local index
  // (i.e., a possibly different number of entries per row).
  constant_num_packets = 0;
 
  const size_t num_export_lids(export_lids.extent(0));
  TEUCHOS_TEST_FOR_EXCEPTION(num_export_lids != size_t(num_packets_per_lid.extent(0)),
                             std::invalid_argument, prefix << "num_export_lids.extent(0) = " << num_export_lids << " != num_packets_per_lid.extent(0) = " << num_packets_per_lid.extent(0) << ".");
  if (num_export_lids != 0) {
    TEUCHOS_TEST_FOR_EXCEPTION(num_packets_per_lid.data() == nullptr, std::invalid_argument,
                               prefix << "num_export_lids = " << num_export_lids << " != 0, but "
                                                                                    "num_packets_per_lid.data() = "
                                      << num_packets_per_lid.data() << " == NULL.");
  }
 
  if (num_export_lids == 0) {
    exports = exports_view_type("exports", 0);
    return;
  }
 
  // Array of offsets into the pack buffer.
  View<size_t*, buffer_device_type> offsets("offsets", num_export_lids + 1);
 
  // Compute number of packets per LID (row to send), as well as
  // corresponding offsets (the prefix sum of the packet counts).
  const size_t count =
      computeNumPacketsAndOffsets(offsets, num_packets_per_lid,
                                  local_graph.row_map, export_lids, export_pids);
 
  // Resize the output pack buffer if needed.
  if (count > size_t(exports.extent(0))) {
    exports = exports_view_type("exports", count);
    if (debug) {
      std::ostringstream os;
      os << "*** exports resized to " << count << std::endl;
      std::cerr << os.str();
    }
  }
  if (debug) {
    std::ostringstream os;
    os << "*** count: " << count << ", exports.extent(0): "
       << exports.extent(0) << std::endl;
    std::cerr << os.str();
  }
 
  // If exports has nonzero length at this point, then the graph has
  // at least one entry to pack.  Thus, if packing process ranks, we
  // had better have at least one process rank to pack.
  TEUCHOS_TEST_FOR_EXCEPTION(pack_pids && exports.extent(0) != 0 &&
                                 export_pids.extent(0) == 0,
                             std::invalid_argument, prefix << "pack_pids is true, and exports.extent(0) = " << exports.extent(0) << " != 0, meaning that we need to pack at least "
                                                                                                                                    "one graph entry, but export_pids.extent(0) = 0.");
 
  exports.modify_device();
  auto exports_d = exports.view_device();
  do_pack<packet_type, local_graph_device_type, local_map_type, buffer_device_type>(local_graph, local_col_map, exports_d, num_packets_per_lid,
                                                                                    export_lids, export_pids, offsets, pack_pids);
  // If we got this far, we succeeded.
}
 
}  // namespace PackCrsGraphImpl
 
template <typename LO, typename GO, typename NT>
void packCrsGraph(const CrsGraph<LO, GO, NT>& sourceGraph,
                  Teuchos::Array<typename CrsGraph<LO, GO, NT>::packet_type>& exports,
                  const Teuchos::ArrayView<size_t>& numPacketsPerLID,
                  const Teuchos::ArrayView<const LO>& exportLIDs,
                  size_t& constantNumPackets) {
  using Kokkos::HostSpace;
  using Kokkos::MemoryUnmanaged;
  using Kokkos::View;
  using crs_graph_type = CrsGraph<LO, GO, NT>;
  using packet_type    = typename crs_graph_type::packet_type;
  using BDT            = typename crs_graph_type::buffer_device_type;
 
  // Convert all Teuchos::Array to Kokkos::View
 
  // This is an output array, so we don't have to copy to device here.
  // However, we'll have to remember to copy back to host when done.
  BDT outputDevice;
  View<size_t*, BDT> num_packets_per_lid_d =
      create_mirror_view_from_raw_host_array(outputDevice,
                                             numPacketsPerLID.getRawPtr(),
                                             numPacketsPerLID.size(), false,
                                             "num_packets_per_lid");
  // This is an input array, so we have to copy to device here.
  // However, we never need to copy it back to host.
  View<const LO*, BDT> export_lids_d =
      create_mirror_view_from_raw_host_array(outputDevice,
                                             exportLIDs.getRawPtr(),
                                             exportLIDs.size(), true,
                                             "export_lids");
  View<const int*, BDT> export_pids_d;
  Kokkos::DualView<packet_type*, BDT> exports_dv;
  constexpr bool pack_pids = false;
 
  static_assert(std::is_same<
                    typename decltype(num_packets_per_lid_d)::non_const_value_type,
                    size_t>::value,
                "num_packets_per_lid_d's non_const_value_type should be size_t.");
  static_assert(std::is_same<
                    typename decltype(num_packets_per_lid_d)::device_type,
                    BDT>::value,
                "num_packets_per_lid_d's BDT should be size_t.");
  static_assert(std::is_same<
                    typename decltype(export_lids_d)::device_type,
                    BDT>::value,
                "export_lids_d's device_type should be BDT.");
  static_assert(std::is_same<
                    typename decltype(export_pids_d)::non_const_value_type,
                    int>::value,
                "export_pids_d's non_const_value_type should be int.");
  static_assert(std::is_same<
                    typename decltype(export_pids_d)::device_type,
                    BDT>::value,
                "export_pids_d's device_type should be BDT.");
 
  PackCrsGraphImpl::packCrsGraph(sourceGraph, exports_dv, num_packets_per_lid_d, export_lids_d,
                                 export_pids_d, constantNumPackets, pack_pids);
 
  // The counts are an output of packCrsGraph, so we have to copy
  // them back to host.
  View<size_t*, HostSpace, MemoryUnmanaged>
      num_packets_per_lid_h(numPacketsPerLID.getRawPtr(),
                            numPacketsPerLID.size());
 
  // DEEP_COPY REVIEW - DEVICE-TO-HOST
  using execution_space = typename BDT::execution_space;
  Kokkos::deep_copy(execution_space(), num_packets_per_lid_h, num_packets_per_lid_d);
 
  // FIXME (mfh 23 Aug 2017) If we're forced to use a DualView for
  // exports_dv above, then we have two host copies for exports_h.
 
  // The exports are an output of packCrsGraph, so we have to
  // copy them back to host.
  if (static_cast<size_t>(exports.size()) !=
      static_cast<size_t>(exports_dv.extent(0))) {
    exports.resize(exports_dv.extent(0));
  }
  View<packet_type*, HostSpace, MemoryUnmanaged>
      exports_h(exports.getRawPtr(), exports.size());
  // DEEP_COPY REVIEW - DEVICE-TO-HOST
  Kokkos::deep_copy(execution_space(), exports_h, exports_dv.view_device());
  execution_space().fence();
}
 
template <typename LO, typename GO, typename NT>
void packCrsGraphNew(const CrsGraph<LO, GO, NT>& sourceGraph,
                     const Kokkos::DualView<
                         const LO*,
                         typename CrsGraph<LO, GO, NT>::buffer_device_type>& export_lids,
                     const Kokkos::DualView<
                         const int*,
                         typename CrsGraph<LO, GO, NT>::buffer_device_type>& export_pids,
                     Kokkos::DualView<
                         typename CrsGraph<LO, GO, NT>::packet_type*,
                         typename CrsGraph<LO, GO, NT>::buffer_device_type>& exports,
                     Kokkos::DualView<
                         size_t*,
                         typename CrsGraph<LO, GO, NT>::buffer_device_type>
                         num_packets_per_lid,
                     size_t& constant_num_packets,
                     const bool pack_pids) {
  using Kokkos::View;
  using crs_graph_type         = CrsGraph<LO, GO, NT>;
  using BDT                    = typename crs_graph_type::buffer_device_type;
  using PT                     = typename crs_graph_type::packet_type;
  using exports_dual_view_type = Kokkos::DualView<PT*, BDT>;
  using LGT                    = typename crs_graph_type::local_graph_device_type;
  using LMT                    = typename crs_graph_type::map_type::local_map_type;
  const char prefix[]          = "Tpetra::Details::packCrsGraphNew: ";
 
  const LGT local_graph   = sourceGraph.getLocalGraphDevice();
  const LMT local_col_map = sourceGraph.getColMap()->getLocalMap();
 
  // Setting this to zero tells the caller to expect a possibly
  // different ("nonconstant") number of packets per local index
  // (i.e., a possibly different number of entries per row).
  constant_num_packets = 0;
 
  const size_t num_export_lids =
      static_cast<size_t>(export_lids.extent(0));
  TEUCHOS_TEST_FOR_EXCEPTION(num_export_lids !=
                                 static_cast<size_t>(num_packets_per_lid.extent(0)),
                             std::invalid_argument, prefix << "num_export_lids.extent(0) = " << num_export_lids << " != num_packets_per_lid.extent(0) = " << num_packets_per_lid.extent(0) << ".");
  TEUCHOS_TEST_FOR_EXCEPTION(num_export_lids != 0 &&
                                 num_packets_per_lid.view_device().data() == nullptr,
                             std::invalid_argument, prefix << "num_export_lids = " << num_export_lids << " != 0, but num_packets_per_lid.view_device().data() = nullptr.");
 
  if (num_export_lids == 0) {
    exports = exports_dual_view_type();
    return;
  }
 
  // Array of offsets into the pack buffer.
  using offsets_type = Kokkos::View<size_t*, BDT>;
  offsets_type offsets("offsets", num_export_lids + 1);
 
  // Compute number of packets per LID (row to send), as well as
  // corresponding offsets (the prefix sum of the packet counts).
  num_packets_per_lid.clear_sync_state();
  num_packets_per_lid.modify_device();
  using PackCrsGraphImpl::computeNumPacketsAndOffsets;
  const size_t count =
      computeNumPacketsAndOffsets(offsets, num_packets_per_lid.view_device(),
                                  local_graph.row_map,
                                  export_lids.view_device(),
                                  export_pids.view_device());
 
  // Resize the output pack buffer if needed.
  if (count > static_cast<size_t>(exports.extent(0))) {
    exports = exports_dual_view_type("exports", count);
  }
 
  // If exports has nonzero length at this point, then the graph has
  // at least one entry to pack.  Thus, if packing process ranks, we
  // had better have at least one process rank to pack.
  TEUCHOS_TEST_FOR_EXCEPTION(pack_pids && exports.extent(0) != 0 &&
                                 export_pids.extent(0) == 0,
                             std::invalid_argument, prefix << "pack_pids is true, and exports.extent(0) = " << exports.extent(0) << " != 0, meaning that we need to pack at least "
                                                                                                                                    "one graph entry, but export_pids.extent(0) = 0.");
 
  exports.modify_device();
  using PackCrsGraphImpl::do_pack;
  do_pack<PT, LGT, LMT, BDT>(local_graph, local_col_map,
                             exports.view_device(),
                             num_packets_per_lid.view_device(),
                             export_lids.view_device(),
                             export_pids.view_device(),
                             offsets, pack_pids);
}
 
template <typename LO, typename GO, typename NT>
void packCrsGraphWithOwningPIDs(const CrsGraph<LO, GO, NT>& sourceGraph,
                                Kokkos::DualView<
                                    typename CrsGraph<LO, GO, NT>::packet_type*,
                                    typename CrsGraph<LO, GO, NT>::buffer_device_type>& exports_dv,
                                const Teuchos::ArrayView<size_t>& numPacketsPerLID,
                                const Teuchos::ArrayView<const LO>& exportLIDs,
                                const Teuchos::ArrayView<const int>& sourcePIDs,
                                size_t& constantNumPackets) {
  using Kokkos::HostSpace;
  using Kokkos::MemoryUnmanaged;
  using Kokkos::View;
  using crs_graph_type     = CrsGraph<LO, GO, NT>;
  using buffer_device_type = typename crs_graph_type::buffer_device_type;
 
  // Convert all Teuchos::Array to Kokkos::View
 
  // This is an output array, so we don't have to copy to device here.
  // However, we'll have to remember to copy back to host when done.
  View<size_t*, buffer_device_type> num_packets_per_lid_d =
      create_mirror_view_from_raw_host_array(buffer_device_type(),
                                             numPacketsPerLID.getRawPtr(),
                                             numPacketsPerLID.size(), false,
                                             "num_packets_per_lid");
 
  // This is an input array, so we have to copy to device here.
  // However, we never need to copy it back to host.
  View<const LO*, buffer_device_type> export_lids_d =
      create_mirror_view_from_raw_host_array(buffer_device_type(),
                                             exportLIDs.getRawPtr(),
                                             exportLIDs.size(), true,
                                             "export_lids");
  // This is an input array, so we have to copy to device here.
  // However, we never need to copy it back to host.
  View<const int*, buffer_device_type> export_pids_d =
      create_mirror_view_from_raw_host_array(buffer_device_type(),
                                             sourcePIDs.getRawPtr(),
                                             sourcePIDs.size(), true,
                                             "export_pids");
  constexpr bool pack_pids = true;
  PackCrsGraphImpl::packCrsGraph(sourceGraph, exports_dv, num_packets_per_lid_d, export_lids_d,
                                 export_pids_d, constantNumPackets, pack_pids);
 
  // The counts are an output of packCrsGraph, so we
  // have to copy them back to host.
  View<size_t*, HostSpace, MemoryUnmanaged> num_packets_per_lid_h(numPacketsPerLID.getRawPtr(), numPacketsPerLID.size());
  // DEEP_COPY REVIEW - DEVICE-TO-HOST
  using execution_space = typename buffer_device_type::execution_space;
  Kokkos::deep_copy(execution_space(),
                    num_packets_per_lid_h, num_packets_per_lid_d);
  execution_space().fence();
}
 
}  // namespace Details
}  // namespace Tpetra
 
#define TPETRA_DETAILS_PACKCRSGRAPH_INSTANT(LO, GO, NT)                                                \
  template void                                                                                        \
  Details::packCrsGraph<LO, GO, NT>(                                                                   \
      const CrsGraph<LO, GO, NT>&,                                                                     \
      Teuchos::Array<CrsGraph<LO, GO, NT>::packet_type>&,                                              \
      const Teuchos::ArrayView<size_t>&,                                                               \
      const Teuchos::ArrayView<const LO>&,                                                             \
      size_t&);                                                                                        \
  template void                                                                                        \
  Details::packCrsGraphNew<LO, GO, NT>(                                                                \
      const CrsGraph<LO, GO, NT>&,                                                                     \
      const Kokkos::DualView<                                                                          \
          const LO*,                                                                                   \
          CrsGraph<LO, GO, NT>::buffer_device_type>&,                                                  \
      const Kokkos::DualView<                                                                          \
          const int*,                                                                                  \
          CrsGraph<LO, GO, NT>::buffer_device_type>&,                                                  \
      Kokkos::DualView<                                                                                \
          CrsGraph<LO, GO, NT>::packet_type*,                                                          \
          CrsGraph<LO, GO, NT>::buffer_device_type>&,                                                  \
      Kokkos::DualView<                                                                                \
          size_t*,                                                                                     \
          CrsGraph<LO, GO, NT>::buffer_device_type>,                                                   \
      size_t&,                                                                                         \
      const bool);                                                                                     \
  template void                                                                                        \
  Details::packCrsGraphWithOwningPIDs<LO, GO, NT>(                                                     \
      const CrsGraph<LO, GO, NT>&,                                                                     \
      Kokkos::DualView<CrsGraph<LO, GO, NT>::packet_type*, CrsGraph<LO, GO, NT>::buffer_device_type>&, \
      const Teuchos::ArrayView<size_t>&,                                                               \
      const Teuchos::ArrayView<const LO>&,                                                             \
      const Teuchos::ArrayView<const int>&,                                                            \
      size_t&);
 
#endif  // TPETRA_DETAILS_PACKCRSGRAPH_DEF_HPP