reduce_optional.hpp

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/*
 * Copyright (C) 2022 The ESPResSo project
 *
 * This file is part of ESPResSo.
 *
 * ESPResSo is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * ESPResSo is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
#ifndef UTILS_MPI_REDUCE_OPTIONAL_HPP
#define UTILS_MPI_REDUCE_OPTIONAL_HPP
 
#include <boost/mpi/collectives/all_reduce.hpp>
#include <boost/mpi/communicator.hpp>
 
#include <cassert>
#include <functional>
#include <optional>
 
namespace Utils::Mpi {
 
/**
 * @brief Reduce an optional on the head node.
 * Worker nodes get a default-constructed object.
 */
template <typename T>
T reduce_optional(boost::mpi::communicator const &comm,
                  std::optional<T> const &result) {
  assert(1 == boost::mpi::all_reduce(comm, static_cast<int>(!!result),
                                     std::plus<>()) &&
         "Incorrect number of return values");
  if (comm.rank() == 0) {
    if (result) {
      return *result;
    }
    T value;
    comm.recv(boost::mpi::any_source, 42, value);
    return value;
  }
  if (result) {
    comm.send(0, 42, *result);
  }
  return {};
}
 
} // namespace Utils::Mpi
 
#endif