Tpetra_DistObject_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

// clang-format off
#ifndef TPETRA_DISTOBJECT_DEF_HPP
#define TPETRA_DISTOBJECT_DEF_HPP


#include "Tpetra_Distributor.hpp"
#include "Tpetra_Details_reallocDualViewIfNeeded.hpp"
#include "Tpetra_Details_Behavior.hpp"
#include "Tpetra_Details_checkGlobalError.hpp"
#include "Tpetra_Details_Profiling.hpp"
#include "Tpetra_Util.hpp" // Details::createPrefix
#include "Teuchos_CommHelpers.hpp"
#include "Teuchos_TypeNameTraits.hpp"
#include <typeinfo>
#include <memory>
#include <sstream>

namespace Tpetra {

  namespace { // (anonymous)
    template<class DeviceType, class IndexType = size_t>
    struct SumFunctor {
      SumFunctor (const Kokkos::View<const size_t*, DeviceType>& viewToSum) :
        viewToSum_ (viewToSum) {}
      KOKKOS_INLINE_FUNCTION void operator() (const IndexType i, size_t& lclSum) const {
        lclSum += viewToSum_(i);
      }
      Kokkos::View<const size_t*, DeviceType> viewToSum_;
    };

    template<class DeviceType, class IndexType = size_t>
    size_t
    countTotalImportPackets (const Kokkos::View<const size_t*, DeviceType>& numImportPacketsPerLID)
    {
      using Kokkos::parallel_reduce;
      typedef DeviceType DT;
      typedef typename DT::execution_space DES;
      typedef Kokkos::RangePolicy<DES, IndexType> range_type;

      const IndexType numOut = numImportPacketsPerLID.extent (0);
      size_t totalImportPackets = 0;
      parallel_reduce ("Count import packets",
                       range_type (0, numOut),
                       SumFunctor<DeviceType, IndexType> (numImportPacketsPerLID),
                       totalImportPackets);
      return totalImportPackets;
    }
  } // namespace (anonymous)


  template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
  DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::
  DistObject (const Teuchos::RCP<const map_type>& map) :
    map_ (map) {}

  template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
  std::string
  DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::
  description () const
  {
    using Teuchos::TypeNameTraits;

    std::ostringstream os;
    os << "\"Tpetra::DistObject\": {"
       << "Packet: " << TypeNameTraits<packet_type>::name ()
       << ", LocalOrdinal: " << TypeNameTraits<local_ordinal_type>::name ()
       << ", GlobalOrdinal: " << TypeNameTraits<global_ordinal_type>::name ()
       << ", Node: " << TypeNameTraits<Node>::name ();
    if (this->getObjectLabel () != "") {
      os << "Label: \"" << this->getObjectLabel () << "\"";
    }
    os << "}";
    return os.str ();
  }

  template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
  void
  DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::
  describe (Teuchos::FancyOStream &out,
            const Teuchos::EVerbosityLevel verbLevel) const
  {
    using Teuchos::rcpFromRef;
    using Teuchos::TypeNameTraits;
    using std::endl;
    const Teuchos::EVerbosityLevel vl = (verbLevel == Teuchos::VERB_DEFAULT) ?
      Teuchos::VERB_LOW : verbLevel;
    Teuchos::RCP<const Teuchos::Comm<int> > comm = this->getMap ()->getComm ();
    const int myRank = comm.is_null () ? 0 : comm->getRank ();
    const int numProcs = comm.is_null () ? 1 : comm->getSize ();

    if (vl != Teuchos::VERB_NONE) {
      Teuchos::OSTab tab0 (out);
      if (myRank == 0) {
        out << "\"Tpetra::DistObject\":" << endl;
      }
      Teuchos::OSTab tab1 (out);
      if (myRank == 0) {
        out << "Template parameters:" << endl;
        {
          Teuchos::OSTab tab2 (out);
          out << "Packet: " << TypeNameTraits<packet_type>::name () << endl
              << "LocalOrdinal: " << TypeNameTraits<local_ordinal_type>::name () << endl
              << "GlobalOrdinal: " << TypeNameTraits<global_ordinal_type>::name () << endl
              << "Node: " << TypeNameTraits<node_type>::name () << endl;
        }
        if (this->getObjectLabel () != "") {
          out << "Label: \"" << this->getObjectLabel () << "\"" << endl;
        }
      } // if myRank == 0

      // Describe the Map.
      {
        if (myRank == 0) {
          out << "Map:" << endl;
        }
        Teuchos::OSTab tab2 (out);
        map_->describe (out, vl);
      }

      // At verbosity > VERB_LOW, each process prints something.
      if (vl > Teuchos::VERB_LOW) {
        for (int p = 0; p < numProcs; ++p) {
          if (myRank == p) {
            out << "Process " << myRank << ":" << endl;
            Teuchos::OSTab tab2 (out);
            out << "Export buffer size (in packets): "
                << exports_.extent (0)
                << endl
                << "Import buffer size (in packets): "
                << imports_.extent (0)
                << endl;
          }
          if (! comm.is_null ()) {
            comm->barrier (); // give output time to finish
            comm->barrier ();
            comm->barrier ();
          }
        } // for each process rank p
      } // if vl > VERB_LOW
    } // if vl != VERB_NONE
  }

  template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
  void
  DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::
  removeEmptyProcessesInPlace (const Teuchos::RCP<const map_type>& /* newMap */)
  {
    TEUCHOS_TEST_FOR_EXCEPTION(true, std::logic_error,
      "Tpetra::DistObject::removeEmptyProcessesInPlace: Not implemented");
  }

  /* These are provided in base DistObject template
  template<class DistObjectType>
  void
  removeEmptyProcessesInPlace (Teuchos::RCP<DistObjectType>& input,
                               const Teuchos::RCP<const Map<typename DistObjectType::local_ordinal_type,
                                                            typename DistObjectType::global_ordinal_type,
                                                            typename DistObjectType::node_type> >& newMap)
  {
    input->removeEmptyProcessesInPlace (newMap);
    if (newMap.is_null ()) { // my process is excluded
      input = Teuchos::null;
    }
  }

  template<class DistObjectType>
  void
  removeEmptyProcessesInPlace (Teuchos::RCP<DistObjectType>& input)
  {
    using Teuchos::RCP;
    typedef typename DistObjectType::local_ordinal_type LO;
    typedef typename DistObjectType::global_ordinal_type GO;
    typedef typename DistObjectType::node_type NT;
    typedef Map<LO, GO, NT> map_type;

    RCP<const map_type> newMap = input->getMap ()->removeEmptyProcesses ();
    removeEmptyProcessesInPlace<DistObjectType> (input, newMap);
  }
  */

  template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
  void
  DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::
  doImport (const SrcDistObject& source,
            const Import<LocalOrdinal, GlobalOrdinal, Node>& importer,
            const CombineMode CM,
            const bool restrictedMode)
  {
    using Details::Behavior;
    using std::endl;
    const char modeString[] = "doImport (forward mode)";

    // mfh 18 Oct 2017: Set TPETRA_VERBOSE to true for copious debug
    // output to std::cerr on every MPI process.  This is unwise for
    // runs with large numbers of MPI processes.
    const bool verbose = Behavior::verbose("DistObject");
    std::unique_ptr<std::string> prefix;
    if (verbose) {
      prefix = this->createPrefix("DistObject", modeString);
      std::ostringstream os;
      os << *prefix << "Start" << endl;
      std::cerr << os.str ();
    }
    this->beginImport(source, importer, CM, restrictedMode);
    this->endImport(source, importer, CM, restrictedMode);
    if (verbose) {
      std::ostringstream os;
      os << *prefix << "Done" << endl;
      std::cerr << os.str ();
    }
  }

  template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
  void
  DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::
  doExport (const SrcDistObject& source,
            const Export<LocalOrdinal, GlobalOrdinal, Node>& exporter,
            const CombineMode CM,
            const bool restrictedMode)
  {
    using Details::Behavior;
    using std::endl;
    const char modeString[] = "doExport (forward mode)";

    // mfh 18 Oct 2017: Set TPETRA_VERBOSE to true for copious debug
    // output to std::cerr on every MPI process.  This is unwise for
    // runs with large numbers of MPI processes.
    const bool verbose = Behavior::verbose("DistObject");
    std::unique_ptr<std::string> prefix;
    if (verbose) {
      prefix = this->createPrefix("DistObject", modeString);
      std::ostringstream os;
      os << *prefix << "Start" << endl;
      std::cerr << os.str ();
    }
    this->beginExport(source, exporter, CM, restrictedMode);
    this->endExport(source, exporter, CM, restrictedMode);
    if (verbose) {
      std::ostringstream os;
      os << *prefix << "Done" << endl;
      std::cerr << os.str ();
    }
  }

  template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
  void
  DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::
  doImport (const SrcDistObject& source,
            const Export<LocalOrdinal, GlobalOrdinal, Node>& exporter,
            const CombineMode CM,
            const bool restrictedMode)
  {
    using Details::Behavior;
    using std::endl;
    const char modeString[] = "doImport (reverse mode)";

    // mfh 18 Oct 2017: Set TPETRA_VERBOSE to true for copious debug
    // output to std::cerr on every MPI process.  This is unwise for
    // runs with large numbers of MPI processes.
    const bool verbose = Behavior::verbose("DistObject");
    std::unique_ptr<std::string> prefix;
    if (verbose) {
      prefix = this->createPrefix("DistObject", modeString);
      std::ostringstream os;
      os << *prefix << "Start" << endl;
      std::cerr << os.str ();
    }
    this->beginImport(source, exporter, CM, restrictedMode);
    this->endImport(source, exporter, CM, restrictedMode);
    if (verbose) {
      std::ostringstream os;
      os << *prefix << "Done" << endl;
      std::cerr << os.str ();
    }
  }

  template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
  void
  DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::
  doExport (const SrcDistObject& source,
            const Import<LocalOrdinal, GlobalOrdinal, Node> & importer,
            const CombineMode CM,
            const bool restrictedMode)
  {
    using Details::Behavior;
    using std::endl;
    const char modeString[] = "doExport (reverse mode)";

    // mfh 18 Oct 2017: Set TPETRA_VERBOSE to true for copious debug
    // output to std::cerr on every MPI process.  This is unwise for
    // runs with large numbers of MPI processes.
    const bool verbose = Behavior::verbose("DistObject");
    std::unique_ptr<std::string> prefix;
    if (verbose) {
      prefix = this->createPrefix("DistObject", modeString);
      std::ostringstream os;
      os << *prefix << "Start" << endl;
      std::cerr << os.str ();
    }
    this->beginExport(source, importer, CM, restrictedMode);
    this->endExport(source, importer, CM, restrictedMode);
    if (verbose) {
      std::ostringstream os;
      os << *prefix << "Done" << endl;
      std::cerr << os.str ();
    }
  }

  template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
  void
  DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::
  beginImport(const SrcDistObject& source,
              const Import<LocalOrdinal, GlobalOrdinal, Node>& importer,
              const CombineMode CM,
              const bool restrictedMode)
  {
    using Details::Behavior;
    using std::endl;
    const char modeString[] = "beginImport (forward mode)";

    // mfh 18 Oct 2017: Set TPETRA_VERBOSE to true for copious debug
    // output to std::cerr on every MPI process.  This is unwise for
    // runs with large numbers of MPI processes.
    const bool verbose = Behavior::verbose("DistObject");
    std::unique_ptr<std::string> prefix;
    if (verbose) {
      prefix = this->createPrefix("DistObject", modeString);
      std::ostringstream os;
      os << *prefix << "Start" << endl;
      std::cerr << os.str ();
    }
    this->beginTransfer(source, importer, modeString, DoForward, CM, restrictedMode);
    if (verbose) {
      std::ostringstream os;
      os << *prefix << "Done" << endl;
      std::cerr << os.str ();
    }
  }

  template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
  void
  DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::
  beginExport(const SrcDistObject& source,
              const Export<LocalOrdinal, GlobalOrdinal, Node>& exporter,
              const CombineMode CM,
              const bool restrictedMode)
  {
    using Details::Behavior;
    using std::endl;
    const char modeString[] = "beginExport (forward mode)";

    // mfh 18 Oct 2017: Set TPETRA_VERBOSE to true for copious debug
    // output to std::cerr on every MPI process.  This is unwise for
    // runs with large numbers of MPI processes.
    const bool verbose = Behavior::verbose("DistObject");
    std::unique_ptr<std::string> prefix;
    if (verbose) {
      prefix = this->createPrefix("DistObject", modeString);
      std::ostringstream os;
      os << *prefix << "Start" << endl;
      std::cerr << os.str ();
    }
    this->beginTransfer(source, exporter, modeString, DoForward, CM, restrictedMode);
    if (verbose) {
      std::ostringstream os;
      os << *prefix << "Done" << endl;
      std::cerr << os.str ();
    }
  }

  template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
  void
  DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::
  beginImport(const SrcDistObject& source,
              const Export<LocalOrdinal, GlobalOrdinal, Node>& exporter,
              const CombineMode CM,
              const bool restrictedMode)
  {
    using Details::Behavior;
    using std::endl;
    const char modeString[] = "beginImport (reverse mode)";

    // mfh 18 Oct 2017: Set TPETRA_VERBOSE to true for copious debug
    // output to std::cerr on every MPI process.  This is unwise for
    // runs with large numbers of MPI processes.
    const bool verbose = Behavior::verbose("DistObject");
    std::unique_ptr<std::string> prefix;
    if (verbose) {
      prefix = this->createPrefix("DistObject", modeString);
      std::ostringstream os;
      os << *prefix << "Start" << endl;
      std::cerr << os.str ();
    }
    this->beginTransfer(source, exporter, modeString, DoReverse, CM, restrictedMode);
    if (verbose) {
      std::ostringstream os;
      os << *prefix << "Done" << endl;
      std::cerr << os.str ();
    }
  }

  template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
  void
  DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::
  beginExport(const SrcDistObject& source,
              const Import<LocalOrdinal, GlobalOrdinal, Node> & importer,
              const CombineMode CM,
              const bool restrictedMode)
  {
    using Details::Behavior;
    using std::endl;
    const char modeString[] = "beginExport (reverse mode)";

    // mfh 18 Oct 2017: Set TPETRA_VERBOSE to true for copious debug
    // output to std::cerr on every MPI process.  This is unwise for
    // runs with large numbers of MPI processes.
    const bool verbose = Behavior::verbose("DistObject");
    std::unique_ptr<std::string> prefix;
    if (verbose) {
      prefix = this->createPrefix("DistObject", modeString);
      std::ostringstream os;
      os << *prefix << "Start" << endl;
      std::cerr << os.str ();
    }
    this->beginTransfer(source, importer, modeString, DoReverse, CM, restrictedMode);
    if (verbose) {
      std::ostringstream os;
      os << *prefix << "Done" << endl;
      std::cerr << os.str ();
    }
  }

  template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
  void
  DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::
  endImport(const SrcDistObject& source,
            const Import<LocalOrdinal, GlobalOrdinal, Node>& importer,
            const CombineMode CM,
            const bool restrictedMode)
  {
    using Details::Behavior;
    using std::endl;
    const char modeString[] = "endImport (forward mode)";

    // mfh 18 Oct 2017: Set TPETRA_VERBOSE to true for copious debug
    // output to std::cerr on every MPI process.  This is unwise for
    // runs with large numbers of MPI processes.
    const bool verbose = Behavior::verbose("DistObject");
    std::unique_ptr<std::string> prefix;
    if (verbose) {
      prefix = this->createPrefix("DistObject", modeString);
      std::ostringstream os;
      os << *prefix << "Start" << endl;
      std::cerr << os.str ();
    }
    this->endTransfer(source, importer, modeString, DoForward, CM, restrictedMode);
    if (verbose) {
      std::ostringstream os;
      os << *prefix << "Done" << endl;
      std::cerr << os.str ();
    }
  }

  template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
  void
  DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::
  endExport(const SrcDistObject& source,
            const Export<LocalOrdinal, GlobalOrdinal, Node>& exporter,
            const CombineMode CM,
            const bool restrictedMode)
  {
    using Details::Behavior;
    using std::endl;
    const char modeString[] = "endExport (forward mode)";

    // mfh 18 Oct 2017: Set TPETRA_VERBOSE to true for copious debug
    // output to std::cerr on every MPI process.  This is unwise for
    // runs with large numbers of MPI processes.
    const bool verbose = Behavior::verbose("DistObject");
    std::unique_ptr<std::string> prefix;
    if (verbose) {
      prefix = this->createPrefix("DistObject", modeString);
      std::ostringstream os;
      os << *prefix << "Start" << endl;
      std::cerr << os.str ();
    }
    this->endTransfer(source, exporter, modeString, DoForward, CM, restrictedMode);
    if (verbose) {
      std::ostringstream os;
      os << *prefix << "Done" << endl;
      std::cerr << os.str ();
    }
  }

  template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
  void
  DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::
  endImport(const SrcDistObject& source,
            const Export<LocalOrdinal, GlobalOrdinal, Node>& exporter,
            const CombineMode CM,
            const bool restrictedMode)
  {
    using Details::Behavior;
    using std::endl;
    const char modeString[] = "endImport (reverse mode)";

    // mfh 18 Oct 2017: Set TPETRA_VERBOSE to true for copious debug
    // output to std::cerr on every MPI process.  This is unwise for
    // runs with large numbers of MPI processes.
    const bool verbose = Behavior::verbose("DistObject");
    std::unique_ptr<std::string> prefix;
    if (verbose) {
      prefix = this->createPrefix("DistObject", modeString);
      std::ostringstream os;
      os << *prefix << "Start" << endl;
      std::cerr << os.str ();
    }
    this->endTransfer(source, exporter, modeString, DoReverse, CM, restrictedMode);
    if (verbose) {
      std::ostringstream os;
      os << *prefix << "Done" << endl;
      std::cerr << os.str ();
    }
  }

  template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
  void
  DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::
  endExport(const SrcDistObject& source,
            const Import<LocalOrdinal, GlobalOrdinal, Node> & importer,
            const CombineMode CM,
            const bool restrictedMode)
  {
    using Details::Behavior;
    using std::endl;
    const char modeString[] = "endExport (reverse mode)";

    // mfh 18 Oct 2017: Set TPETRA_VERBOSE to true for copious debug
    // output to std::cerr on every MPI process.  This is unwise for
    // runs with large numbers of MPI processes.
    const bool verbose = Behavior::verbose("DistObject");
    std::unique_ptr<std::string> prefix;
    if (verbose) {
      prefix = this->createPrefix("DistObject", modeString);
      std::ostringstream os;
      os << *prefix << "Start" << endl;
      std::cerr << os.str ();
    }
    this->endTransfer(source, importer, modeString, DoReverse, CM, restrictedMode);
    if (verbose) {
      std::ostringstream os;
      os << *prefix << "Done" << endl;
      std::cerr << os.str ();
    }
  }

  template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
  bool
  DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::
  transferArrived() const {
    return distributorActor_.isReady();
  }

  template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
  bool
  DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::
  isDistributed () const {
    return map_->isDistributed ();
  }

  template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
  size_t
  DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::
  constantNumberOfPackets () const {
    return 0; // default implementation; subclasses may override
  }

  template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
  void
  DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::
  doTransfer (const SrcDistObject& src,
              const ::Tpetra::Details::Transfer<local_ordinal_type, global_ordinal_type, node_type>& transfer,
              const char modeString[],
              const ReverseOption revOp,
              const CombineMode CM,
              bool restrictedMode)
  {
    beginTransfer(src, transfer, modeString, revOp, CM, restrictedMode);
    endTransfer(src, transfer, modeString, revOp, CM, restrictedMode);
  }

  template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
  bool
  DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::
  reallocImportsIfNeeded (const size_t newSize,
                          const bool verbose,
                          const std::string* prefix,
                          const bool /*remoteLIDsContiguous*/,
                          const CombineMode /*CM*/)
  {
    if (verbose) {
      std::ostringstream os;
      os << *prefix << "Realloc (if needed) imports_ from "
         << imports_.extent (0) << " to " << newSize << std::endl;
      std::cerr << os.str ();
    }
    using ::Tpetra::Details::reallocDualViewIfNeeded;
    const bool reallocated =
      reallocDualViewIfNeeded (this->imports_, newSize, "imports");
    if (verbose) {
      std::ostringstream os;
      os << *prefix << "Finished realloc'ing imports_" << std::endl;
      std::cerr << os.str ();
    }
    return reallocated;
  }

  template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
  bool
  DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::
  reallocArraysForNumPacketsPerLid (const size_t numExportLIDs,
                                    const size_t numImportLIDs)
  {
    using Details::Behavior;
    using ::Tpetra::Details::dualViewStatusToString;
    using ::Tpetra::Details::reallocDualViewIfNeeded;
    using std::endl;
    // If an array is already allocated, and if is at least
    // tooBigFactor times bigger than it needs to be, free it and
    // reallocate to the size we need, in order to save space.
    // Otherwise, take subviews to reduce allocation size.
    constexpr size_t tooBigFactor = 10;

    const bool verbose = Behavior::verbose("DistObject");
    std::unique_ptr<std::string> prefix;
    if (verbose) {
      prefix = this->createPrefix("DistObject",
        "reallocArraysForNumPacketsPerLid");
      std::ostringstream os;
      os << *prefix
         << "numExportLIDs: " << numExportLIDs
         << ", numImportLIDs: " << numImportLIDs
         << endl;
      os << *prefix << "DualView status before:" << endl
         << *prefix
         << dualViewStatusToString (this->numExportPacketsPerLID_,
                                    "numExportPacketsPerLID_")
         << endl
         << *prefix
         << dualViewStatusToString (this->numImportPacketsPerLID_,
                                    "numImportPacketsPerLID_")
         << endl;
      std::cerr << os.str ();
    }

    // Reallocate numExportPacketsPerLID_ if needed.
    const bool firstReallocated =
      reallocDualViewIfNeeded (this->numExportPacketsPerLID_,
                               numExportLIDs,
                               "numExportPacketsPerLID",
                               tooBigFactor,
                               true); // need fence before, if realloc'ing

    // If we reallocated above, then we fenced after that
    // reallocation.  This means that we don't need to fence again,
    // before the next reallocation.
    const bool needFenceBeforeNextAlloc = ! firstReallocated;
    const bool secondReallocated =
      reallocDualViewIfNeeded (this->numImportPacketsPerLID_,
                               numImportLIDs,
                               "numImportPacketsPerLID",
                               tooBigFactor,
                               needFenceBeforeNextAlloc);

    if (verbose) {
      std::ostringstream os;
      os << *prefix << "DualView status after:" << endl
         << *prefix << dualViewStatusToString (this->numExportPacketsPerLID_,
                                               "numExportPacketsPerLID_")
         << endl
         << *prefix << dualViewStatusToString (this->numImportPacketsPerLID_,
                                               "numImportPacketsPerLID_")
         << endl;
      std::cerr << os.str ();
    }

    return firstReallocated || secondReallocated;
  }

  template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
  void
  DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::
  beginTransfer(const SrcDistObject& src,
                const ::Tpetra::Details::Transfer<local_ordinal_type, global_ordinal_type, node_type>& transfer,
                const char modeString[],
                const ReverseOption revOp,
                const CombineMode CM,
                bool restrictedMode)
  {
    using Details::Behavior;
    using ::Tpetra::Details::dualViewStatusToString;
    using ::Tpetra::Details::getArrayViewFromDualView;
    using Details::ProfilingRegion;
    using Kokkos::Compat::getArrayView;
    using Kokkos::Compat::getConstArrayView;
    using Kokkos::Compat::getKokkosViewDeepCopy;
    using Kokkos::Compat::create_const_view;
    using std::endl;
    using Details::getDualViewCopyFromArrayView;
    using Details::ProfilingRegion;

    const bool commOnHost = ! Behavior::assumeMpiIsGPUAware ();
    const char funcNameHost[] = "Tpetra::DistObject::beginTransfer[Host]";
    const char funcNameDevice[] = "Tpetra::DistObject::beginTransfer[Device]";
    const char *funcName = commOnHost ? funcNameHost : funcNameDevice;

    ProfilingRegion region_doTransfer(funcName);
    const bool verbose = Behavior::verbose("DistObject");
    std::shared_ptr<std::string> prefix;
    if (verbose) {
      std::ostringstream os;
      prefix = this->createPrefix("DistObject", "doTransfer");
      os << *prefix << "Source type: " << Teuchos::typeName(src)
         << ", Target type: " << Teuchos::typeName(*this) << endl;
      std::cerr << os.str();
    }

    // "Restricted Mode" does two things:
    // 1) Skips copyAndPermute
    // 2) Allows the "target" Map of the transfer to be a subset of
    //    the Map of *this, in a "locallyFitted" sense.
    //
    // This cannot be used if #2 is not true, OR there are permutes.
    // Source Maps still need to match

    // mfh 18 Oct 2017: Set TPETRA_DEBUG to true to enable extra debug
    // checks.  These may communicate more.
    const bool debug = Behavior::debug("DistObject");
    if (debug) {
      if (! restrictedMode && revOp == DoForward) {
        const bool myMapSameAsTransferTgtMap =
          this->getMap ()->isSameAs (* (transfer.getTargetMap ()));
        TEUCHOS_TEST_FOR_EXCEPTION
          (! myMapSameAsTransferTgtMap, std::invalid_argument,
           "Tpetra::DistObject::" << modeString << ": For forward-mode "
           "communication, the target DistObject's Map must be the same "
           "(in the sense of Tpetra::Map::isSameAs) as the input "
           "Export/Import object's target Map.");
      }
      else if (! restrictedMode && revOp == DoReverse) {
        const bool myMapSameAsTransferSrcMap =
          this->getMap ()->isSameAs (* (transfer.getSourceMap ()));
        TEUCHOS_TEST_FOR_EXCEPTION
          (! myMapSameAsTransferSrcMap, std::invalid_argument,
           "Tpetra::DistObject::" << modeString << ": For reverse-mode "
           "communication, the target DistObject's Map must be the same "
         "(in the sense of Tpetra::Map::isSameAs) as the input "
           "Export/Import object's source Map.");
      }
      else if (restrictedMode && revOp == DoForward) {
        const bool myMapLocallyFittedTransferTgtMap =
          this->getMap ()->isLocallyFitted (* (transfer.getTargetMap ()));
        TEUCHOS_TEST_FOR_EXCEPTION
          (! myMapLocallyFittedTransferTgtMap , std::invalid_argument,
           "Tpetra::DistObject::" << modeString << ": For forward-mode "
           "communication using restricted mode, Export/Import object's "
           "target Map must be locally fitted (in the sense of "
           "Tpetra::Map::isLocallyFitted) to target DistObject's Map.");
      }
      else { // if (restrictedMode && revOp == DoReverse)
        const bool myMapLocallyFittedTransferSrcMap =
          this->getMap ()->isLocallyFitted (* (transfer.getSourceMap ()));
        TEUCHOS_TEST_FOR_EXCEPTION
          (! myMapLocallyFittedTransferSrcMap, std::invalid_argument,
           "Tpetra::DistObject::" << modeString << ": For reverse-mode "
           "communication using restricted mode, Export/Import object's "
           "source Map must be locally fitted (in the sense of "
           "Tpetra::Map::isLocallyFitted) to target DistObject's Map.");
      }

      // SrcDistObject need not even _have_ Maps.  However, if the
      // source object is a DistObject, it has a Map, and we may
      // compare that Map with the Transfer's Maps.
      const this_type* srcDistObj = dynamic_cast<const this_type*> (&src);
      if (srcDistObj != nullptr) {
        if (revOp == DoForward) {
          const bool srcMapSameAsImportSrcMap =
            srcDistObj->getMap ()->isSameAs (* (transfer.getSourceMap ()));
          TEUCHOS_TEST_FOR_EXCEPTION
            (! srcMapSameAsImportSrcMap, std::invalid_argument,
             "Tpetra::DistObject::" << modeString << ": For forward-mode "
             "communication, the source DistObject's Map must be the same "
             "as the input Export/Import object's source Map.");
        }
        else { // revOp == DoReverse
          const bool srcMapSameAsImportTgtMap =
            srcDistObj->getMap ()->isSameAs (* (transfer.getTargetMap ()));
          TEUCHOS_TEST_FOR_EXCEPTION
            (! srcMapSameAsImportTgtMap, std::invalid_argument,
             "Tpetra::DistObject::" << modeString << ": For reverse-mode "
             "communication, the source DistObject's Map must be the same "
             "as the input Export/Import object's target Map.");
        }
      }
    }

    const size_t numSameIDs = transfer.getNumSameIDs ();
    Distributor& distor = transfer.getDistributor ();
    const Details::DistributorPlan& distributorPlan = (revOp == DoForward) ? distor.getPlan() : *distor.getPlan().getReversePlan();

    TEUCHOS_TEST_FOR_EXCEPTION
      (debug && restrictedMode &&
       (transfer.getPermuteToLIDs_dv().extent(0) != 0 ||
        transfer.getPermuteFromLIDs_dv().extent(0) != 0),
       std::invalid_argument,
       "Tpetra::DistObject::" << modeString << ": Transfer object "
       "cannot have permutes in restricted mode.");

    // Do we need all communication buffers to live on host?
    if (verbose) {
      std::ostringstream os;
      os << *prefix << "doTransfer: Use new interface; "
        "commOnHost=" << (commOnHost ? "true" : "false") << endl;
      std::cerr << os.str ();
    }

    using const_lo_dv_type =
      Kokkos::DualView<const local_ordinal_type*, buffer_device_type>;
    const_lo_dv_type permuteToLIDs = (revOp == DoForward) ?
      transfer.getPermuteToLIDs_dv () :
      transfer.getPermuteFromLIDs_dv ();
    const_lo_dv_type permuteFromLIDs = (revOp == DoForward) ?
      transfer.getPermuteFromLIDs_dv () :
      transfer.getPermuteToLIDs_dv ();
    const_lo_dv_type remoteLIDs = (revOp == DoForward) ?
      transfer.getRemoteLIDs_dv () :
      transfer.getExportLIDs_dv ();
    const_lo_dv_type exportLIDs = (revOp == DoForward) ?
      transfer.getExportLIDs_dv () :
      transfer.getRemoteLIDs_dv ();
    const bool canTryAliasing = (revOp == DoForward) ?
      transfer.areRemoteLIDsContiguous() :
      transfer.areExportLIDsContiguous();
    // const bool canTryAliasing = false;

    ProfilingRegion region_dTN(funcName);

    if (verbose) {
      std::ostringstream os;
      os << *prefix << "Input arguments:" << endl
         << *prefix << "  combineMode: " << combineModeToString (CM) << endl
         << *prefix << "  numSameIDs: " << numSameIDs << endl
         << *prefix << "  "
         << dualViewStatusToString (permuteToLIDs, "permuteToLIDs") << endl
         << *prefix << "  "
         << dualViewStatusToString (permuteFromLIDs, "permuteFromLIDs") << endl
         << *prefix << "  "
         << dualViewStatusToString (remoteLIDs, "remoteLIDs") << endl
         << *prefix << "  "
         << dualViewStatusToString (exportLIDs, "exportLIDs") << endl
         << *prefix << "  revOp: Do" << (revOp == DoReverse ? "Reverse" : "Forward") << endl
         << *prefix << "  commOnHost: " << (commOnHost ? "true" : "false") << endl;
      std::cerr << os.str ();
    }

    {
      ProfilingRegion region_cs ("Tpetra::DistObject::beginTransfer::checkSizes");
      if (verbose) {
        std::ostringstream os;
        os << *prefix << "1. checkSizes" << endl;
        std::cerr << os.str ();
      }
      const bool checkSizesResult = this->checkSizes (src);
      TEUCHOS_TEST_FOR_EXCEPTION
        (! checkSizesResult, std::invalid_argument,
         "Tpetra::DistObject::doTransfer: checkSizes() indicates that the "
         "destination object is not a legal target for redistribution from the "
         "source object.  This probably means that they do not have the same "
         "dimensions.  For example, MultiVectors must have the same number of "
         "rows and columns.");
    }

    // The method may return zero even if the implementation actually
    // does have a constant number of packets per LID.  However, if it
    // returns nonzero, we may use this information to avoid
    // (re)allocating num{Ex,Im}portPacketsPerLID_.  packAndPrepare()
    // will set this to its final value.
    //
    // We only need this if CM != ZERO, but it has to be lifted out of
    // that scope because there are multiple tests for CM != ZERO.
    size_t constantNumPackets = this->constantNumberOfPackets ();
    if (verbose) {
      std::ostringstream os;
      os << *prefix << "constantNumPackets=" << constantNumPackets << endl;
      std::cerr << os.str ();
    }

    // Do we need to do communication?
    bool needCommunication = true;
    // We only need to send data if the combine mode is not ZERO.
    if (CM != ZERO) {
      // This may be NULL.  It will be used below.
      const this_type* srcDistObj = dynamic_cast<const this_type*> (&src);

      if (revOp == DoReverse && ! this->isDistributed ()) {
        needCommunication = false;
      }
      // FIXME (mfh 30 Jun 2013): Checking whether the source object
      // is distributed requires a cast to DistObject.  If it's not a
      // DistObject, then I'm not quite sure what to do.  Perhaps it
      // would be more appropriate for SrcDistObject to have an
      // isDistributed() method.  For now, I'll just assume that we
      // need to do communication unless the cast succeeds and the
      // source is not distributed.
      else if (revOp == DoForward && srcDistObj != NULL &&
               ! srcDistObj->isDistributed ()) {
        needCommunication = false;
      }
    } // if (CM != ZERO)
    else {
     needCommunication = false;
    }

    // The operations for the transfer can be performed in different
    // order. The "safe" way is
    //
    // - copyAndPermute     |
    // - packAndPrepare     |--- beginTransfer
    // - doPostRecvs        |
    // - doPostSends        |
    //
    // - doWaitsRecv        |
    // - unpackAndCombine   |--- endTransfer
    // - doWaitsSend        |

    // This is "safe" because the local computation steps
    // copyAndPermute and packAndPrepare are free to run on host or
    // device provided that the data is appropriately synced.
    // Afterwards, all the communication options can run independently
    // of the computation. This means that there are no constraints in
    // terms of memory spaces out of which the different steps need to
    // run.

    // However, for performance it can be beneficial to overlap
    // communication and computation, leading to this sequence of
    // operations:
    //
    // - doPostRecvs       |
    // - packAndPrepare    |--- beginTransfer
    // - doPostSends       |
    // - copyAndPermute    |
    //
    // - doWaitsRecv       |
    // - unpackAndCombine  |--- endTransfer
    // - doWaitsSend       |
    //
    // Note that this is not the same as overlap of communication and
    // computation in the sparse matrix-vector product which would involve
    // performing computation between beginTransfer and endTransfer.
    //
    // The second approach has two advantages:
    // 1) Receives and sends are separated by computation. This
    // decreases the likelihood of MPI having to allocate temporary
    // buffers for unexpectedly received messages.
    // 2) Sends and doWaitsRecv in endTransfer are seperated by
    // copyAndPermute, giving MPI time to make progress.
    //
    // The downside of this approach is as follows. The imports view
    // used for the receives is potentially aliased to a subview of
    // the target. This means that MPI will modify the target in the
    // memory space that is determined by GPU awareness
    // (Behavior::assumeMpiIsGPUAware). Since copyAndPermute will also
    // be writing to the target at the same time, it will need to
    // modify target in the same space.
    //
    // Given these additional constraints, we currently only enable
    // the overlapping of communication and computation when constantNumPackets > 0
    // and Behavior::enableGranularTransfers().

    const bool overlapTransferSteps = (constantNumPackets != 0) && Behavior::enableGranularTransfers();

    if (verbose) {
      std::ostringstream os;
      os << *prefix << "overlapTransferSteps=" << overlapTransferSteps << endl;
      std::cerr << os.str ();
    }

    // Decide whether copyAndPermute needs to be run.
    const bool thereAreIDsToCopy = (numSameIDs + permuteToLIDs.extent (0) != 0);
    const bool needCopyAndPermute = (!restrictedMode && thereAreIDsToCopy);

    if ( ! overlapTransferSteps ) {

      // copyAndPermute

      // NOTE (mfh 26 Apr 2016) Chris Baker's implementation understood
      // that if CM == INSERT || CM == REPLACE, the target object could
      // be write only.  We don't optimize for that here.

      if ( needCopyAndPermute ) {
        // There is at least one GID to copy or permute.

        if (verbose) {
          std::ostringstream os;
          os << *prefix << "2. copyAndPermute" << endl;
          std::cerr << os.str ();
        }
        {
          ProfilingRegion region_cp ("Tpetra::DistObject::beginTransfer::copyAndPermute");

          this->copyAndPermute (src, numSameIDs, permuteToLIDs, permuteFromLIDs, CM);
        }
        if (verbose) {
          std::ostringstream os;
          os << *prefix << "After copyAndPermute:" << endl
          << *prefix << "  "
          << dualViewStatusToString (permuteToLIDs, "permuteToLIDs")
          << endl
          << *prefix << "  "
          << dualViewStatusToString (permuteFromLIDs, "permuteFromLIDs")
          << endl;
          std::cerr << os.str ();
        }
      }

      if ( ! needCommunication ) {
        if (verbose) {
          std::ostringstream os;
          os << *prefix << "Comm not needed; skipping" << endl;
          std::cerr << os.str ();
        }
      }
      else {
        // packAndPrepare

        if (constantNumPackets == 0) {
          if (verbose) {
            std::ostringstream os;
            os << *prefix << "3. (Re)allocate num{Ex,Im}portPacketsPerLID"
               << endl;
            std::cerr << os.str ();
          }
          // This only reallocates if necessary, that is, if the sizes
          // don't match.
          this->reallocArraysForNumPacketsPerLid (exportLIDs.extent (0),
                                                  remoteLIDs.extent (0));
        }

        if (verbose) {
          std::ostringstream os;
          os << *prefix << "4. packAndPrepare: before, "
             << dualViewStatusToString (this->exports_, "exports_")
             << endl;
          std::cerr << os.str ();
        }

        doPackAndPrepare(src, exportLIDs, constantNumPackets, execution_space());
        if (commOnHost) {
          this->exports_.sync_host();
        }
        else {
          this->exports_.sync_device();
        }

        if (verbose) {
          std::ostringstream os;
          os << *prefix << "5.1. After packAndPrepare, "
             << dualViewStatusToString (this->exports_, "exports_")
             << endl;
          std::cerr << os.str ();
        }

        // reallocImportsIfNeeded
        if (constantNumPackets != 0) {
          ProfilingRegion region_reallocImportsIfNeeded("Tpetra::DistObject::beginTransfer::reallocImportsIfNeeded");

          // There are a constant number of packets per element.  We
          // already know (from the number of "remote" (incoming)
          // elements) how many incoming elements we expect, so we can
          // resize the buffer accordingly.
          const size_t rbufLen = remoteLIDs.extent (0) * constantNumPackets;
          reallocImportsIfNeeded (rbufLen, verbose, prefix.get (), canTryAliasing, CM);
        }

        // doPostRecvs

        // If only one round of communication is required: post receives.
        // If two rounds are required: complete first round and post receives for second round.
        if (verbose) {
          std::ostringstream os;
          os << *prefix << "7.0. "
             << (revOp == DoReverse ? "Reverse" : "Forward")
             << " mode" << endl;
          std::cerr << os.str ();
        }

        doPostRecvs(distributorPlan, constantNumPackets, commOnHost, prefix, canTryAliasing, CM);

        // doPostSends

        doPostSends(distributorPlan, constantNumPackets, commOnHost, prefix);
      } // if ( needCommunication )

    } // if ( ! overlapTransferSteps )
    else {

      // Overlap local computation with communication

      if ( ! needCommunication ) {
        if (verbose) {
          std::ostringstream os;
          os << *prefix << "Comm not needed; skipping" << endl;
          std::cerr << os.str ();
        }
      }
      else {

        // doPostRecvs

        // reallocImportsIfNeeded
        if (constantNumPackets != 0) {
          ProfilingRegion region_reallocImportsIfNeeded("Tpetra::DistObject::beginTransfer::reallocImportsIfNeeded");

          // There are a constant number of packets per element.  We
          // already know (from the number of "remote" (incoming)
          // elements) how many incoming elements we expect, so we can
          // resize the buffer accordingly.
          const size_t rbufLen = remoteLIDs.extent (0) * constantNumPackets;
          reallocImportsIfNeeded (rbufLen, verbose, prefix.get (), canTryAliasing, CM);
        }

        // If only one round of communication is required: post receives.
        // If two rounds are required: complete first round and post receives for second round.
        if (verbose) {
          std::ostringstream os;
          os << *prefix << "7.0. "
             << (revOp == DoReverse ? "Reverse" : "Forward")
             << " mode" << endl;
          std::cerr << os.str ();
        }

        doPostRecvs(distributorPlan, constantNumPackets, commOnHost, prefix, canTryAliasing, CM);

        // packAndPrepare

        if (constantNumPackets == 0) {
          if (verbose) {
            std::ostringstream os;
            os << *prefix << "3. (Re)allocate num{Ex,Im}portPacketsPerLID"
               << endl;
            std::cerr << os.str ();
          }
          // This only reallocates if necessary, that is, if the sizes
          // don't match.
          this->reallocArraysForNumPacketsPerLid (exportLIDs.extent (0),
                                                  remoteLIDs.extent (0));
        }

        if (verbose) {
          std::ostringstream os;
          os << *prefix << "4. packAndPrepare: before, "
             << dualViewStatusToString (this->exports_, "exports_")
             << endl;
          std::cerr << os.str ();
        }

        doPackAndPrepare(src, exportLIDs, constantNumPackets, execution_space());

        if (commOnHost) {
          this->exports_.sync_host();
        }
        else {
          this->exports_.sync_device();
        }

        if (verbose) {
          std::ostringstream os;
          os << *prefix << "5.1. After packAndPrepare, "
             << dualViewStatusToString (this->exports_, "exports_")
             << endl;
          std::cerr << os.str ();
        }

        // doPostSends

        doPostSends(distributorPlan, constantNumPackets, commOnHost, prefix);

      } // if ( needCommunication )

      // copyAndPermute

      // NOTE (mfh 26 Apr 2016) Chris Baker's implementation understood
      // that if CM == INSERT || CM == REPLACE, the target object could
      // be write only.  We don't optimize for that here.

      if ( needCopyAndPermute ) {
        // There is at least one GID to copy or permute.
        if (verbose) {
          std::ostringstream os;
          os << *prefix << "2. copyAndPermute" << endl;
          std::cerr << os.str ();
        }

        {
          ProfilingRegion region_cp("Tpetra::DistObject::beginTransfer::copyAndPermute");

          this->copyAndPermute (src, numSameIDs, permuteToLIDs, permuteFromLIDs, CM);
        }

        if (verbose) {
          std::ostringstream os;
          os << *prefix << "After copyAndPermute:" << endl
          << *prefix << "  "
          << dualViewStatusToString (permuteToLIDs, "permuteToLIDs")
          << endl
          << *prefix << "  "
          << dualViewStatusToString (permuteFromLIDs, "permuteFromLIDs")
          << endl;
          std::cerr << os.str ();
        }
      }
    } // if ( overlapTransferSteps )
  }

  template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
  void
  DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::
  endTransfer(const SrcDistObject& src,
              const ::Tpetra::Details::Transfer<local_ordinal_type, global_ordinal_type, node_type>& transfer,
              const char modeString[],
              const ReverseOption revOp,
              const CombineMode CM,
              bool restrictedMode)
  {
    using Details::Behavior;
    using ::Tpetra::Details::dualViewStatusToString;
    using ::Tpetra::Details::getArrayViewFromDualView;
    using Details::ProfilingRegion;
    using Kokkos::Compat::getArrayView;
    using Kokkos::Compat::getConstArrayView;
    using Kokkos::Compat::getKokkosViewDeepCopy;
    using Kokkos::Compat::create_const_view;
    using std::endl;
    using Details::getDualViewCopyFromArrayView;
    using Details::ProfilingRegion;

    const bool commOnHost = ! Behavior::assumeMpiIsGPUAware ();
    const char funcNameHost[] = "Tpetra::DistObject::endTransfer[Host]";
    const char funcNameDevice[] = "Tpetra::DistObject::endTransfer[Device]";
    const char *funcName = commOnHost ? funcNameHost : funcNameDevice;
    ProfilingRegion region_doTransfer(funcName);
    const bool verbose = Behavior::verbose("DistObject");
    std::shared_ptr<std::string> prefix;
    if (verbose) {
      std::ostringstream os;
      prefix = this->createPrefix("DistObject", "doTransfer");
      os << *prefix << "Source type: " << Teuchos::typeName(src)
         << ", Target type: " << Teuchos::typeName(*this) << endl;
      std::cerr << os.str();
    }

    // "Restricted Mode" does two things:
    // 1) Skips copyAndPermute
    // 2) Allows the "target" Map of the transfer to be a subset of
    //    the Map of *this, in a "locallyFitted" sense.
    //
    // This cannot be used if #2 is not true, OR there are permutes.
    // Source Maps still need to match

    // mfh 18 Oct 2017: Set TPETRA_DEBUG to true to enable extra debug
    // checks.  These may communicate more.
    const bool debug = Behavior::debug("DistObject");
    if (debug) {
      if (! restrictedMode && revOp == DoForward) {
        const bool myMapSameAsTransferTgtMap =
          this->getMap ()->isSameAs (* (transfer.getTargetMap ()));
        TEUCHOS_TEST_FOR_EXCEPTION
          (! myMapSameAsTransferTgtMap, std::invalid_argument,
           "Tpetra::DistObject::" << modeString << ": For forward-mode "
           "communication, the target DistObject's Map must be the same "
           "(in the sense of Tpetra::Map::isSameAs) as the input "
           "Export/Import object's target Map.");
      }
      else if (! restrictedMode && revOp == DoReverse) {
        const bool myMapSameAsTransferSrcMap =
          this->getMap ()->isSameAs (* (transfer.getSourceMap ()));
        TEUCHOS_TEST_FOR_EXCEPTION
          (! myMapSameAsTransferSrcMap, std::invalid_argument,
           "Tpetra::DistObject::" << modeString << ": For reverse-mode "
           "communication, the target DistObject's Map must be the same "
         "(in the sense of Tpetra::Map::isSameAs) as the input "
           "Export/Import object's source Map.");
      }
      else if (restrictedMode && revOp == DoForward) {
        const bool myMapLocallyFittedTransferTgtMap =
          this->getMap ()->isLocallyFitted (* (transfer.getTargetMap ()));
        TEUCHOS_TEST_FOR_EXCEPTION
          (! myMapLocallyFittedTransferTgtMap , std::invalid_argument,
           "Tpetra::DistObject::" << modeString << ": For forward-mode "
           "communication using restricted mode, Export/Import object's "
           "target Map must be locally fitted (in the sense of "
           "Tpetra::Map::isLocallyFitted) to target DistObject's Map.");
      }
      else { // if (restrictedMode && revOp == DoReverse)
        const bool myMapLocallyFittedTransferSrcMap =
          this->getMap ()->isLocallyFitted (* (transfer.getSourceMap ()));
        TEUCHOS_TEST_FOR_EXCEPTION
          (! myMapLocallyFittedTransferSrcMap, std::invalid_argument,
           "Tpetra::DistObject::" << modeString << ": For reverse-mode "
           "communication using restricted mode, Export/Import object's "
           "source Map must be locally fitted (in the sense of "
           "Tpetra::Map::isLocallyFitted) to target DistObject's Map.");
      }

      // SrcDistObject need not even _have_ Maps.  However, if the
      // source object is a DistObject, it has a Map, and we may
      // compare that Map with the Transfer's Maps.
      const this_type* srcDistObj = dynamic_cast<const this_type*> (&src);
      if (srcDistObj != nullptr) {
        if (revOp == DoForward) {
          const bool srcMapSameAsImportSrcMap =
            srcDistObj->getMap ()->isSameAs (* (transfer.getSourceMap ()));
          TEUCHOS_TEST_FOR_EXCEPTION
            (! srcMapSameAsImportSrcMap, std::invalid_argument,
             "Tpetra::DistObject::" << modeString << ": For forward-mode "
             "communication, the source DistObject's Map must be the same "
             "as the input Export/Import object's source Map.");
        }
        else { // revOp == DoReverse
          const bool srcMapSameAsImportTgtMap =
            srcDistObj->getMap ()->isSameAs (* (transfer.getTargetMap ()));
          TEUCHOS_TEST_FOR_EXCEPTION
            (! srcMapSameAsImportTgtMap, std::invalid_argument,
             "Tpetra::DistObject::" << modeString << ": For reverse-mode "
             "communication, the source DistObject's Map must be the same "
             "as the input Export/Import object's target Map.");
        }
      }
    }

    Distributor& distor = transfer.getDistributor ();
    const Details::DistributorPlan& distributorPlan = (revOp == DoForward) ? distor.getPlan() : *distor.getPlan().getReversePlan();

    TEUCHOS_TEST_FOR_EXCEPTION
      (debug && restrictedMode &&
       (transfer.getPermuteToLIDs_dv().extent(0) != 0 ||
        transfer.getPermuteFromLIDs_dv().extent(0) != 0),
       std::invalid_argument,
       "Tpetra::DistObject::" << modeString << ": Transfer object "
       "cannot have permutes in restricted mode.");

    // Do we need all communication buffers to live on host?
    if (verbose) {
      std::ostringstream os;
      os << *prefix << "doTransfer: Use new interface; "
        "commOnHost=" << (commOnHost ? "true" : "false") << endl;
      std::cerr << os.str ();
    }

    using const_lo_dv_type =
      Kokkos::DualView<const local_ordinal_type*, buffer_device_type>;
    const_lo_dv_type remoteLIDs = (revOp == DoForward) ?
      transfer.getRemoteLIDs_dv () :
      transfer.getExportLIDs_dv ();

    size_t constantNumPackets = this->constantNumberOfPackets ();

    // We only need to send data if the combine mode is not ZERO.
    if (CM != ZERO) {
      // Do we need to do communication (via doWaitsRecv and doWaitsSend)?
      bool needCommunication = true;

      // This may be NULL.  It will be used below.
      const this_type* srcDistObj = dynamic_cast<const this_type*> (&src);

      if (revOp == DoReverse && ! this->isDistributed ()) {
        needCommunication = false;
      }
      // FIXME (mfh 30 Jun 2013): Checking whether the source object
      // is distributed requires a cast to DistObject.  If it's not a
      // DistObject, then I'm not quite sure what to do.  Perhaps it
      // would be more appropriate for SrcDistObject to have an
      // isDistributed() method.  For now, I'll just assume that we
      // need to do communication unless the cast succeeds and the
      // source is not distributed.
      else if (revOp == DoForward && srcDistObj != NULL &&
               ! srcDistObj->isDistributed ()) {
        needCommunication = false;
      }

      if (! needCommunication) {
        if (verbose) {
          std::ostringstream os;
          os << *prefix << "Comm not needed; skipping" << endl;
          std::cerr << os.str ();
        }
      }
      else {
        distributorActor_.doWaitsRecv(distributorPlan);

        if (verbose) {
          std::ostringstream os;
          os << *prefix << "8. unpackAndCombine - remoteLIDs " << remoteLIDs.extent(0) << ", constantNumPackets " << constantNumPackets << endl;
          std::cerr << os.str ();
        }
        doUnpackAndCombine(remoteLIDs, constantNumPackets, CM, execution_space());

        distributorActor_.doWaitsSend(distributorPlan);
      } // if (needCommunication)
    } // if (CM != ZERO)

    if (verbose) {
      std::ostringstream os;
      os << *prefix << "9. Done!" << endl;
      std::cerr << os.str ();
    }

    if (verbose) {
      std::ostringstream os;
      os << *prefix << "Tpetra::DistObject::doTransfer: Done!" << endl;
      std::cerr << os.str ();
    }
  }

  template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
  void
  DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::
  doPostRecvs(const Details::DistributorPlan& distributorPlan,
              size_t constantNumPackets,
              bool commOnHost,
              std::shared_ptr<std::string> prefix,
              const bool canTryAliasing,
              const CombineMode CM)
  {
    using ::Tpetra::Details::dualViewStatusToString;
    using ::Tpetra::Details::getArrayViewFromDualView;
    using Kokkos::Compat::create_const_view;
    using std::endl;
    using Details::ProfilingRegion;

    const char funcNameHost[] = "Tpetra::DistObject::doPostRecvs[Host]";
    const char funcNameDevice[] = "Tpetra::DistObject::doPostRecvs[Device]";
    const char *funcName = commOnHost ? funcNameHost : funcNameDevice;
    ProfilingRegion region_dpr (funcName);

    const bool verbose = Details::Behavior::verbose("DistObject");

    if (constantNumPackets == 0) { // variable num packets per LID
      if (verbose) {
        std::ostringstream os;
        os << *prefix << "7.1. Variable # packets / LID: first comm "
          << "(commOnHost = " << (commOnHost ? "true" : "false") << ")"
          << endl;
        std::cerr << os.str ();
      }
      size_t totalImportPackets = 0;
      if (commOnHost) {
        if (this->numExportPacketsPerLID_.need_sync_host ()) {
          this->numExportPacketsPerLID_.sync_host ();
        }
        if (this->numImportPacketsPerLID_.need_sync_host ()) {
          this->numImportPacketsPerLID_.sync_host ();
        }
        this->numImportPacketsPerLID_.modify_host (); // out arg
        auto numExp_h =
          create_const_view (this->numExportPacketsPerLID_.view_host ());
        auto numImp_h = this->numImportPacketsPerLID_.view_host ();

        // MPI communication happens here.
        if (verbose) {
          std::ostringstream os;
          os << *prefix << "Call doPostsAndWaits"
            << endl;
          std::cerr << os.str ();
        }
        distributorActor_.doPostsAndWaits(distributorPlan, numExp_h, 1, numImp_h);

        if (verbose) {
          std::ostringstream os;
          os << *prefix << "Count totalImportPackets" << std::endl;
          std::cerr << os.str ();
        }
        using the_dev_type = typename decltype (numImp_h)::device_type;
        totalImportPackets = countTotalImportPackets<the_dev_type> (numImp_h);
      }
      else { // ! commOnHost
        this->numExportPacketsPerLID_.sync_device ();
        this->numImportPacketsPerLID_.sync_device ();
        this->numImportPacketsPerLID_.modify_device (); // out arg
        auto numExp_d = create_const_view
          (this->numExportPacketsPerLID_.view_device ());
        auto numImp_d = this->numImportPacketsPerLID_.view_device ();

        // MPI communication happens here.
        if (verbose) {
          std::ostringstream os;
          os << *prefix << "Call doPostsAndWaits"
            << endl;
          std::cerr << os.str ();
        }

        distributorActor_.doPostsAndWaits(distributorPlan, numExp_d, 1, numImp_d);

        if (verbose) {
          std::ostringstream os;
          os << *prefix << "Count totalImportPackets" << std::endl;
          std::cerr << os.str ();
        }
        using the_dev_type = typename decltype (numImp_d)::device_type;
        totalImportPackets = countTotalImportPackets<the_dev_type> (numImp_d);
      }

      if (verbose) {
        std::ostringstream os;
        os << *prefix << "totalImportPackets=" << totalImportPackets << endl;
        std::cerr << os.str ();
      }
      this->reallocImportsIfNeeded (totalImportPackets, verbose,
                                    prefix.get (), canTryAliasing, CM);
      if (verbose) {
        std::ostringstream os;
        os << *prefix << "7.3. Second comm" << std::endl;
        std::cerr << os.str ();
      }

      // mfh 04 Feb 2019: Distributor expects the "num packets per
      // LID" arrays on host, so that it can issue MPI sends and
      // receives correctly.
      this->numImportPacketsPerLID_.sync_host ();

      // NOTE (mfh 25 Apr 2016, 01 Aug 2017) doPostsAndWaits and
      // doReversePostsAndWaits currently want
      // numExportPacketsPerLID and numImportPacketsPerLID as
      // Teuchos::ArrayView, rather than as Kokkos::View.
      //
      // NOTE (mfh 04 Feb 2019) This does NOT copy from host to
      // device.  The above syncs might.
      auto numImportPacketsPerLID_av =
        getArrayViewFromDualView (this->numImportPacketsPerLID_);

      // imports_ is for output only, so we don't need to sync it
      // before marking it as modified.  However, in order to
      // prevent spurious debug-mode errors (e.g., "modified on
      // both device and host"), we first need to clear its
      // "modified" flags.
      this->imports_.clear_sync_state ();

      if (verbose) {
        std::ostringstream os;
        os << *prefix << "Comm on "
          << (commOnHost ? "host" : "device")
          << "; call doPostRecvs" << endl;
        std::cerr << os.str ();
      }

      if (commOnHost) {
        this->imports_.modify_host ();
        distributorActor_.doPostRecvs
          (distributorPlan,
           this->imports_.view_host (),
           numImportPacketsPerLID_av);
      }
      else { // pack on device
        this->imports_.modify_device ();
        distributorActor_.doPostRecvs
          (distributorPlan,
           this->imports_.view_device (),
           numImportPacketsPerLID_av);
      }
    }
    else { // constant number of packets per LID
      if (verbose) {
        std::ostringstream os;
        os << *prefix << "7.1. Const # packets per LID: " << endl
          << *prefix << "  "
          << dualViewStatusToString (this->exports_, "exports_")
          << endl
          << *prefix << "  "
          << dualViewStatusToString (this->exports_, "imports_")
          << endl;
        std::cerr << os.str ();
      }
      // imports_ is for output only, so we don't need to sync it
      // before marking it as modified.  However, in order to
      // prevent spurious debug-mode errors (e.g., "modified on
      // both device and host"), we first need to clear its
      // "modified" flags.
      this->imports_.clear_sync_state ();

      if (verbose) {
        std::ostringstream os;
        os << *prefix << "7.2. Comm on "
          << (commOnHost ? "host" : "device")
          << "; call doPostRecvs" << endl;
        std::cerr << os.str ();
      }
      if (commOnHost) {
        this->imports_.modify_host ();
        distributorActor_.doPostRecvs
          (distributorPlan,
           constantNumPackets,
           this->imports_.view_host ());
      }
      else { // pack on device
        this->imports_.modify_device ();
        distributorActor_.doPostRecvs
          (distributorPlan,
           constantNumPackets,
           this->imports_.view_device ());
      } // commOnHost
    } // constant or variable num packets per LID
  }

  template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
  void
  DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::
  doPostSends(const Details::DistributorPlan& distributorPlan,
              size_t constantNumPackets,
              bool commOnHost,
              std::shared_ptr<std::string> prefix)
  {
    using ::Tpetra::Details::getArrayViewFromDualView;
    using Kokkos::Compat::create_const_view;
    using std::endl;
    using Details::ProfilingRegion;

    const char funcNameHost[] = "Tpetra::DistObject::doPostSends[Host]";
    const char funcNameDevice[] = "Tpetra::DistObject::doPostSends[Device]";
    const char *funcName = commOnHost ? funcNameHost : funcNameDevice;
    ProfilingRegion region_dps (funcName);

    const bool verbose = Details::Behavior::verbose("DistObject");
    if (verbose) {
      std::ostringstream os;
      os << *prefix << "Comm on "
         << (commOnHost ? "host" : "device")
         << "; call doPostSends" << endl;
      std::cerr << os.str ();
    }

    if (constantNumPackets == 0) { // variable num packets per LID
      // mfh 04 Feb 2019: Distributor expects the "num packets per
      // LID" arrays on host, so that it can issue MPI sends and
      // receives correctly.
      this->numExportPacketsPerLID_.sync_host ();
      this->numImportPacketsPerLID_.sync_host ();

      // NOTE (mfh 25 Apr 2016, 01 Aug 2017) doPostsAndWaits and
      // doReversePostsAndWaits currently want
      // numExportPacketsPerLID and numImportPacketsPerLID as
      // Teuchos::ArrayView, rather than as Kokkos::View.
      //
      // NOTE (mfh 04 Feb 2019) This does NOT copy from host to
      // device.  The above syncs might.
      auto numExportPacketsPerLID_av =
        getArrayViewFromDualView (this->numExportPacketsPerLID_);
      auto numImportPacketsPerLID_av =
        getArrayViewFromDualView (this->numImportPacketsPerLID_);

      if (commOnHost) {
        distributorActor_.doPostSends
          (distributorPlan,
           create_const_view (this->exports_.view_host ()),
           numExportPacketsPerLID_av,
           this->imports_.view_host (),
           numImportPacketsPerLID_av);
      }
      else { // pack on device
        // We need to guarantee that packAndPrepare is done before we send.
        Kokkos::fence("DistObject::doPostSends-1"); // for UVM
        distributorActor_.doPostSends
          (distributorPlan,
           create_const_view (this->exports_.view_device ()),
           numExportPacketsPerLID_av,
           this->imports_.view_device (),
           numImportPacketsPerLID_av);
      }
    }
    else { // constant number of packets per LID
      if (commOnHost) {
        distributorActor_.doPostSends
          (distributorPlan,
           create_const_view (this->exports_.view_host ()),
           constantNumPackets,
           this->imports_.view_host ());
      }
      else { // pack on device
        // We need to guarantee that packAndPrepare is done before we send.
        Kokkos::fence("DistObject::doPostSends-2"); // for UVM
        distributorActor_.doPostSends
          (distributorPlan,
           create_const_view (this->exports_.view_device ()),
           constantNumPackets,
           this->imports_.view_device ());
      } // commOnHost
    } // constant or variable num packets per LID
  }

  template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
  void
  DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::
  doPackAndPrepare(const SrcDistObject& src,
                   const Kokkos::DualView<const local_ordinal_type*, buffer_device_type>& exportLIDs,
                   size_t& constantNumPackets,
                   const execution_space &space)
  {
    using Details::ProfilingRegion;
    using std::endl;
    const bool debug = Details::Behavior::debug("DistObject");

    ProfilingRegion region_pp
      ("Tpetra::DistObject::doPackAndPrepare");

    // Ask the source to pack data.  Also ask it whether there are
    // a constant number of packets per element
    // (constantNumPackets is an output argument).  If there are,
    // constantNumPackets will come back nonzero.  Otherwise, the
    // source will fill the numExportPacketsPerLID_ array.

    // FIXME (mfh 18 Oct 2017) if (! commOnHost), sync to device?
    // Alternately, make packAndPrepare take a "commOnHost"
    // argument to tell it where to leave the data?
    //
    // NOTE (mfh 04 Feb 2019) Subclasses of DistObject should have
    // the freedom to pack and unpack either on host or device.
    // We should prefer sync'ing only on demand.  Thus, we can
    // answer the above question: packAndPrepare should not
    // take a commOnHost argument, and doTransferNew should sync
    // where needed, if needed.
    if (debug) {
      std::ostringstream lclErrStrm;
      bool lclSuccess = false;
      try {
        this->packAndPrepare (src, exportLIDs, this->exports_,
            this->numExportPacketsPerLID_,
            constantNumPackets, space);
        lclSuccess = true;
      }
      catch (std::exception& e) {
        lclErrStrm << "packAndPrepare threw an exception: "
          << endl << e.what();
      }
      catch (...) {
        lclErrStrm << "packAndPrepare threw an exception "
          "not a subclass of std::exception.";
      }
      const char gblErrMsgHeader[] = "Tpetra::DistObject "
        "threw an exception in packAndPrepare on "
        "one or more processes in the DistObject's communicator.";
      auto comm = getMap()->getComm();
      Details::checkGlobalError(std::cerr, lclSuccess,
          lclErrStrm.str().c_str(),
          gblErrMsgHeader, *comm);
    }
    else {
      this->packAndPrepare (src, exportLIDs, this->exports_,
          this->numExportPacketsPerLID_,
          constantNumPackets, space);
    }
  }

  template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
  void
  DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::
  doUnpackAndCombine(const Kokkos::DualView<const local_ordinal_type*, buffer_device_type>& remoteLIDs,
                     size_t constantNumPackets,
                     CombineMode CM,
                     const execution_space &space)
  {
    using Details::ProfilingRegion;
    using std::endl;
    const bool debug = Details::Behavior::debug("DistObject");

    ProfilingRegion region_uc
      ("Tpetra::DistObject::doUnpackAndCombine");

    if (debug) {
      std::ostringstream lclErrStrm;
      bool lclSuccess = false;
      try {
        this->unpackAndCombine (remoteLIDs, this->imports_,
            this->numImportPacketsPerLID_,
            constantNumPackets, CM, space);
        lclSuccess = true;
      }
      catch (std::exception& e) {
        lclErrStrm << "doUnpackAndCombine threw an exception: "
          << endl << e.what();
      }
      catch (...) {
        lclErrStrm << "doUnpackAndCombine threw an exception "
          "not a subclass of std::exception.";
      }
      const char gblErrMsgHeader[] = "Tpetra::DistObject "
        "threw an exception in unpackAndCombine on "
        "one or more processes in the DistObject's communicator.";
      auto comm = getMap()->getComm();
      Details::checkGlobalError(std::cerr, lclSuccess,
          lclErrStrm.str().c_str(),
          gblErrMsgHeader, *comm);
    }
    else {
      this->unpackAndCombine (remoteLIDs, this->imports_,
          this->numImportPacketsPerLID_,
          constantNumPackets, CM, space);
    }
  }

  template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
  void
  DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::
  copyAndPermute
  (const SrcDistObject&,
   const size_t,
   const Kokkos::DualView<
     const local_ordinal_type*,
     buffer_device_type>&,
   const Kokkos::DualView<
     const local_ordinal_type*,
     buffer_device_type>&,
   const CombineMode CM)
  {}

// clang-format on
template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
void DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::copyAndPermute(
    const SrcDistObject &source, const size_t numSameIDs,
    const Kokkos::DualView<const local_ordinal_type *, buffer_device_type>
        &permuteToLIDs,
    const Kokkos::DualView<const local_ordinal_type *, buffer_device_type>
        &permuteFromLIDs,
    const CombineMode CM, const execution_space &space) {
  /*
  This is called if the derived class doesn't know how to pack and prepare in
  an arbitrary execution space instance, but it was asked to anyway.
  Provide a safe illusion by actually doing the work in the default instance,
  and syncing the default instance with the provided instance.
  The caller expects
  1. any work in the provided instance to complete before this.
  2. This to complete before any following work in the provided instance.
  */

  space.fence(); // // TODO: Tpetra::Details::Spaces::exec_space_wait
  copyAndPermute(source, numSameIDs, permuteToLIDs, permuteFromLIDs,
                 CM);        // default instance
  execution_space().fence(); // TODO:
                             // Tpetra::Details::Spaces::exec_space_wait
}
// clang-format off


  template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
  void
  DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::
  packAndPrepare
  (const SrcDistObject&,
   const Kokkos::DualView<
     const local_ordinal_type*,
     buffer_device_type>&,
   Kokkos::DualView<
     packet_type*,
     buffer_device_type>&,
   Kokkos::DualView<
     size_t*,
     buffer_device_type>,
   size_t&)
  {}

// clang-format on
template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
void DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::packAndPrepare(
    const SrcDistObject &source,
    const Kokkos::DualView<const local_ordinal_type *, buffer_device_type>
        &exportLIDs,
    Kokkos::DualView<packet_type *, buffer_device_type> &exports,
    Kokkos::DualView<size_t *, buffer_device_type> numPacketsPerLID,
    size_t &constantNumPackets, const execution_space &space) {
  /*
  This is called if the derived class doesn't know how to pack and prepare in
  an arbitrary execution space instance, but it was asked to anyway.
  Provide a safe illusion by actually doing the work in the default instance,
  and syncing the default instance with the provided instance.

  The caller expects
  1. any work in the provided instance to complete before this.
  2. This to complete before any following work in the provided instance.
  */

  // wait for any work from prior operations in the provided instance to
  // complete
  space.fence(); // TODO: Details::Spaces::exec_space_wait

  // pack and prepare in the default instance.
  packAndPrepare(source, exportLIDs, exports, numPacketsPerLID,
                 constantNumPackets); // default instance

  // wait for the default instance to complete before returning, so any
  // following work inserted into the provided instance will be done after this
  execution_space().fence(); // TODO: Details::Spaces::exec_space_wait
}
// clang-format off

  template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
  void
  DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::
  unpackAndCombine
  (const Kokkos::DualView<
     const local_ordinal_type*,
     buffer_device_type>& /* importLIDs */,
   Kokkos::DualView<
     packet_type*,
     buffer_device_type> /* imports */,
   Kokkos::DualView<
     size_t*,
     buffer_device_type> /* numPacketsPerLID */,
   const size_t /* constantNumPackets */,
   const CombineMode /* combineMode */)
  {}

// clang-format on
template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
void DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::unpackAndCombine(
    const Kokkos::DualView<const local_ordinal_type *, buffer_device_type>
        &importLIDs,
    Kokkos::DualView<packet_type *, buffer_device_type> imports,
    Kokkos::DualView<size_t *, buffer_device_type> numPacketsPerLID,
    const size_t constantNumPackets, const CombineMode combineMode,
    const execution_space &space) {
  // Wait for any work in the provided space to complete
  space.fence(); // TODO: Details::Spaces::exec_space_wait(execution_space(),
                 // space);
  unpackAndCombine(importLIDs, imports, numPacketsPerLID, constantNumPackets,
                   combineMode); // default instance
  // wait for unpack to finish in the default instance, since the caller
  // may be expecting sequential semantics in the `space` instance
  execution_space().fence(); // TODO: Details::Spaces::exec_space_wait(space,
                             // execution_space());
}
// clang-format off

template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
void DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::print(
    std::ostream &os) const {
  using std::endl;
  using Teuchos::FancyOStream;
  using Teuchos::getFancyOStream;
  using Teuchos::RCP;
  using Teuchos::rcpFromRef;

  RCP<FancyOStream> out = getFancyOStream(rcpFromRef(os));
  this->describe(*out, Teuchos::VERB_DEFAULT);
}

template <class Packet, class LocalOrdinal, class GlobalOrdinal, class Node>
std::unique_ptr<std::string>
DistObject<Packet, LocalOrdinal, GlobalOrdinal, Node>::createPrefix(
    const char className[], const char methodName[]) const {
  auto map = this->getMap();
  auto comm = map.is_null() ? Teuchos::null : map->getComm();
  return Details::createPrefix(comm.getRawPtr(), className, methodName);
}

template <class DistObjectType>
void removeEmptyProcessesInPlace(
    Teuchos::RCP<DistObjectType> &input,
    const Teuchos::RCP<const Map<typename DistObjectType::local_ordinal_type,
                                 typename DistObjectType::global_ordinal_type,
                                 typename DistObjectType::node_type>> &newMap) {
  input->removeEmptyProcessesInPlace(newMap);
  if (newMap.is_null()) { // my process is excluded
    input = Teuchos::null;
  }
}

template <class DistObjectType>
void removeEmptyProcessesInPlace(Teuchos::RCP<DistObjectType> &input) {
  auto newMap = input->getMap()->removeEmptyProcesses();
  removeEmptyProcessesInPlace<DistObjectType>(input, newMap);
}

// Explicit instantiation macro for general DistObject.
#define TPETRA_DISTOBJECT_INSTANT(SCALAR, LO, GO, NODE)                        \
  template class DistObject<SCALAR, LO, GO, NODE>;

// Explicit instantiation macro for DistObject<char, ...>.
// The "SLGN" stuff above doesn't work for Packet=char.
#define TPETRA_DISTOBJECT_INSTANT_CHAR(LO, GO, NODE)                           \
  template class DistObject<char, LO, GO, NODE>;

} // namespace Tpetra

#endif // TPETRA_DISTOBJECT_DEF_HPP
// clang-format on