Tpetra_Details_reallocDualViewIfNeeded.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_REALLOCDUALVIEWIFNEEDED_HPP
#define TPETRA_DETAILS_REALLOCDUALVIEWIFNEEDED_HPP


#include "Tpetra_Details_Profiling.hpp"
#include "Kokkos_DualView.hpp"

namespace Tpetra {
namespace Details {

template<class ValueType, class DeviceType>
bool
reallocDualViewIfNeeded (Kokkos::DualView<ValueType*, DeviceType>& dv,
                         const size_t newSize,
                         const char newLabel[],
                         const size_t tooBigFactor = 2,
                         const bool needFenceBeforeRealloc = true)
{
  typedef typename DeviceType::execution_space execution_space;
  typedef Kokkos::DualView<ValueType*, DeviceType> dual_view_type;
  typedef Kokkos::pair<size_t, size_t> range_type;

  // Profiling this matters, because GPU allocations can be expensive.
  using Tpetra::Details::ProfilingRegion;
  ProfilingRegion region ("Tpetra::Details::reallocDualViewIfNeeded");

  const size_t curSize = static_cast<size_t> (dv.extent (0));
  if (curSize == newSize) {
    return false; // did not reallocate
  }
  else if (curSize < newSize) { // too small; need to reallocate
    if (needFenceBeforeRealloc) {
      execution_space().fence (); // keep this fence to respect needFenceBeforeRealloc
    }
    dv = dual_view_type (); // free first, in order to save memory
    // If current size is 0, the DualView's Views likely lack a label.
    dv = dual_view_type (curSize == 0 ? newLabel : dv.view_device().label (), newSize);
    return true; // we did reallocate
  }
  else {
    if (newSize == 0) { // special case: realloc to 0 means always do it
      if (needFenceBeforeRealloc) {
        execution_space().fence (); // keep this fence to respect needFenceBeforeRealloc
      }
      // If current size is 0, the DualView's Views likely lack a label.
      dv = dual_view_type (curSize == 0 ? newLabel : dv.view_device().label (), 0);
      return true; // we did reallocate
    }
    // Instead of writing curSize >= tooBigFactor * newSize, express
    // via division to avoid overflow (for very large right-hand side).
    // We've already tested whether newSize == 0, so this is safe.
    else if (curSize / newSize >= tooBigFactor) {
      // The allocation is much too big, so free it and reallocate
      // to the new, smaller size.
      if (needFenceBeforeRealloc) {
        execution_space().fence (); // keep this fence to respect needFenceBeforeRealloc
      }
      dv = dual_view_type (); // free first, in order to save memory
      // If current size is 0, the DualView's Views likely lack a label.
      dv = dual_view_type (curSize == 0 ? newLabel : dv.view_device().label (), newSize);
      return true; // we did reallocate
    }
    else {
      auto d_view = Kokkos::subview (dv.view_device(), range_type (0, newSize));
      auto h_view = Kokkos::subview (dv.view_host(), range_type (0, newSize));
      dv = Kokkos::DualView<ValueType*, DeviceType>(d_view, h_view);
      return false; // we did not reallocate
    }
  }
}

template<class ValueType, class DeviceType>
bool
reallocDualViewIfNeeded (Kokkos::DualView<ValueType*, DeviceType>& exports,
                         const size_t newSize,
                         const std::string& newLabel,
                         const size_t tooBigFactor = 2,
                         const bool needFenceBeforeRealloc = true)
{
  return reallocDualViewIfNeeded<ValueType, DeviceType> (exports, newSize,
                                                         newLabel.c_str (),
                                                         tooBigFactor,
                                                         needFenceBeforeRealloc);
}

} // namespace Details
} // namespace Tpetra

#endif // TPETRA_DETAILS_REALLOCDUALVIEWIFNEEDED_HPP