group.hpp

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// Copyright (c) 2024 Simons Foundation
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0.txt
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// Authors: Thomas Hahn, Alexander Hampel, Olivier Parcollet, Nils Wentzell

 
#pragma once
 
#include "./communicator.hpp"
#include "./environment.hpp"
#include "./utils.hpp"
 
#include <mpi.h>
 
#include <utility>
#include <vector>
 
namespace mpi {

  class group {
    public:
    group() = default;

    group(group const &) = delete;

    group &operator=(group const &) = delete;

    group(group &&other) noexcept : grp_{std::exchange(other.grp_, MPI_GROUP_NULL)} {}

    group &operator=(group &&rhs) noexcept {
      if (this != std::addressof(rhs)) {
        free();
        grp_ = std::exchange(rhs.grp_, MPI_GROUP_NULL);
      }
      return *this;
    }

    ~group() { free(); }

    explicit group(MPI_Group grp) : grp_(grp) {}

    explicit group(communicator c) {
      if (has_env) check_mpi_call(MPI_Comm_group(c.get(), &grp_), "MPI_Comm_group");
    }

    [[nodiscard]] MPI_Group get() const noexcept { return grp_; }

    [[nodiscard]] bool is_null() const noexcept { return grp_ == MPI_GROUP_NULL; }

    [[nodiscard]] int rank() const {
      int r = 0;
      if (has_env) check_mpi_call(MPI_Group_rank(grp_, &r), "MPI_Group_rank");
      return r;
    }

    [[nodiscard]] int size() const {
      int s = 1;
      if (has_env) check_mpi_call(MPI_Group_size(grp_, &s), "MPI_Group_size");
      return s;
    }

    [[nodiscard]] group include(std::vector<int> const &ranks) const {
      MPI_Group newgroup = MPI_GROUP_NULL;
      if (has_env) check_mpi_call(MPI_Group_incl(grp_, static_cast<int>(ranks.size()), ranks.data(), &newgroup), "MPI_Group_incl");
      return group{newgroup};
    }

    void free() noexcept {
      if (has_env && !is_null()) MPI_Group_free(&grp_);
    }
 
    private:
    MPI_Group grp_ = MPI_GROUP_NULL;
  };
 
} // namespace mpi