text: // Copyright 2016 The TensorFlow Authors. All Rights Reserved.
  // Modifications copyright (C) 2019 Uber Technologies, Inc.
  //
  // 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
  //
  // 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.
  // =============================================================================
  
  #ifndef HOROVOD_MPI_CONTEXT_H
  #define HOROVOD_MPI_CONTEXT_H
  
  #include <iostream>
  #include <memory>
  #include <vector>
  #include <nkmpi.h>
  
  #include "../common.h"
  #include "../half.h"
  #include "../logging.h"
  
  namespace horovod {
  namespace common {
  
  // Base class for managing MPI environment. Can be derived if other frameworks
  // (like DDL) are able to manage MPI environment.
  class MPIContextManager {
  public:
    // Initialize MPI environment with required multi-threads support level.
    virtual void EnvInitialize(int mpi_threads_required);
  
    // Finalize MPI environment.
    virtual void EnvFinalize();
  };
  
  struct MPIContext {
  
    void Enable() {
      enabled_ = true;
      LOG(DEBUG) << "MPI context enabled.";
    };
  
    bool IsEnabled() { return enabled_; }
  
    // Take an argument of context manager pointer that will take care of
    // initialization of MPI environment.
    void Initialize(const std::vector<int>& ranks,
                    std::vector<int>& dims,
                    MPIContextManager& ctx_manager);
  
    // Take an argument of context manager pointer that will take care of
    // finalization of MPI environment.
    void Finalize(MPIContextManager& ctx_manager);
    MPI_Datatype GetMPIDataType(std::shared_ptr<Tensor> tensor);
  
    MPI_Datatype GetMPIDataType(DataType dtype);
  
    MPI_Op GetMPISumOp(DataType dtype);
  
    MPI_Comm GetMPICommunicator(Communicator comm);
  
    int GetMPITypeSize(DataType dtype);
  
    // Flag indicating whether mpi is enabled.
    bool enabled_ = false;
  
    // MPI custom data type for float16.
    MPI_Datatype mpi_float16_t;
    MPI_Op mpi_float16_sum;
  
    // Private MPI communicator for Horovod to ensure no collisions with other
    // threads using MPI.
    MPI_Comm mpi_comm;
  
    // Node-local communicator.
    MPI_Comm local_comm;
  
    // Cross-node communicator for hierarchical allreduce.
    MPI_Comm cross_comm;
  
    // NKMPI context.
    nkmpi::Context nkmpi_ctx;
  
    // MPI Window used for shared memory allgather
    MPI_Win window;
  
    // Whether mpi context should be finalize.
    bool should_finalize = false;
  };
  
  } // namespace common
  } // namespace horovod
  
  #endif // HOROVOD_MPI_CONTEXT_H
  