/* Copyright 2020 The OpenXLA Authors.

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 XLA_PJRT_GPU_NCCL_ID_STORE_H_
#define XLA_PJRT_GPU_NCCL_ID_STORE_H_

#include <memory>
#include <utility>

#include "absl/base/thread_annotations.h"
#include "absl/container/flat_hash_map.h"
#include "absl/status/statusor.h"
#include "absl/synchronization/mutex.h"
#include "xla/backends/gpu/collectives/gpu_clique_key.h"
#include "xla/core/collectives/clique_id.h"
#include "xla/core/collectives/clique_key.h"
#include "xla/pjrt/distributed/key_value_store_interface.h"
#include "xla/service/global_device_id.h"

namespace xla {

// A table mapping GpuCliqueKeys to CliqueIds. In a distributed setup the
// table of NCCL IDs is kept on the master node (node 0). The node of the first
// participating device will create the unique id.
class NcclIdStore {
 public:
  NcclIdStore(int node_id,
              absl::flat_hash_map<GlobalDeviceId, int> device_to_node,
              std::shared_ptr<KeyValueStoreInterface> kv_store)
      : node_id_(node_id),
        device_to_node_(std::move(device_to_node)),
        kv_store_(std::move(kv_store)) {}

  absl::StatusOr<CliqueId> GetNcclUniqueId(const CliqueKey& key);

 private:
  const int node_id_;
  const absl::flat_hash_map<GlobalDeviceId, int> device_to_node_;
  const std::shared_ptr<KeyValueStoreInterface> kv_store_;

  absl::Mutex mu_;
  absl::flat_hash_map<gpu::GpuCliqueKey, CliqueId> cache_ ABSL_GUARDED_BY(mu_);
};

}  // namespace xla

#endif  // XLA_PJRT_GPU_NCCL_ID_STORE_H_