Tpetra_Details_reallocDualViewIfNeeded.hpp

Go to the documentation of this file.

// @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