namespace tf_gcs_filesystem {
typedef struct GcsFileStat {
  TF_FileStatistics base;
  int64_t generation_number;
} GcsFileStat;

typedef struct GCSFile {
  google::cloud::storage::Client gcs_client;  // owned
  bool compose;
  absl::Mutex block_cache_lock;
  std::shared_ptr<RamFileBlockCache> file_block_cache
      ABSL_GUARDED_BY(block_cache_lock);
  uint64_t block_size;  // Reads smaller than block_size will trigger a read

// Fetches the return outputs requested via
// TF_ImportGraphDefOptionsAddReturnOutput(). The number of fetched outputs is
// returned in `num_outputs`. The array of return outputs is returned in
// `outputs`. `*outputs` is owned by and has the lifetime of `results`.
TF_CAPI_EXPORT extern void TF_ImportGraphDefResultsReturnOutputs(
    TF_ImportGraphDefResults* results, int* num_outputs, TF_Output** outputs);

  // For LLVM style RTTI.
  static bool classof(const AbstractContext* ptr) {
    return ptr->getKind() == kTape;
  }
  ~TapeContext() override;

 private:
  AbstractContext* parent_ctx_;  // Not owned.
  Tape* tape_;
  const GradientRegistry& registry_;
};
}  // namespace gradients
}  // namespace tensorflow

// "fifo_queue_enqueue_<tensor_id>", to be executed by this API call. It reads
// from a placeholder node "arg_tensor_enqueue_<tensor_id>".
//
// `tensor` is still owned by the caller. This call will be blocked if the queue
// has reached its capacity, and will be unblocked when the queued tensors again
// drop below the capacity due to dequeuing.
//

      const std::vector<Gradient*>& in_grads, absl::Span<Gradient*> out_grads);

  // Maps from tensor IDs to corresponding JVPs.
  std::unordered_map<int64_t, Gradient*> accumulated_gradients_;
  // Not owned; provides operations on Tensors which are currently only
  // available in language bindings (e.g. Python).
  const VSpace<Gradient, BackwardFunction, TapeTensor>& vspace_;

  // Decides if tangents are vectorized or not

                 std::unique_ptr<tensorflow::Tensor>* out_tensor,
                 TF_Status* out_status) const;

 private:
  // Uses "v2_reader_" to build "var name -> shape" and "var name -> data type"
  // maps; both owned by caller.
  // REQUIRES: "v2_reader_ != nullptr && v2_reader_.status().ok()".
  std::pair<std::unique_ptr<TensorSliceReader::VarToShapeMap>,
            std::unique_ptr<TensorSliceReader::VarToDataTypeMap> >
  BuildV2VarMaps();

};

struct TF_ImportGraphDefOptions {
  tensorflow::ImportGraphDefOptions opts;

  // Backing memory for TensorId fields in opts.
  // TODO(skyewm): it'd be better if ImportGraphDefOptions owned this.
  std::vector<tensorflow::string> tensor_id_data;
};

struct TF_ImportGraphDefResults {
  std::vector<TF_Output> return_tensors;
  std::vector<TF_Operation*> return_nodes;

} TF_Filesystem_Option_Type;

typedef struct TF_Filesystem_Option {
  char* name;                         // null terminated, owned
  char* description;                  // null terminated, owned
  int per_file;                       // bool actually, but bool is not a C type
  TF_Filesystem_Option_Value* value;  // owned
} TF_Filesystem_Option;

/// SECTION 2. Function tables for functionality provided by plugins

      : owned_executor(new tensorflow::EagerExecutor(
            async, enable_streaming_enqueue, in_flight_nodes_limit)) {}

  explicit TFE_Executor(tensorflow::EagerExecutor* executor)
      : owned_executor(nullptr), unowned_executor(executor) {}

  tensorflow::EagerExecutor* executor() {
    return owned_executor == nullptr ? unowned_executor : owned_executor.get();
  }

  Status Name(StringPiece* result) const override;

 private:
  std::string filename_;
  std::unique_ptr<TF_RandomAccessFile> file_;
  const TF_RandomAccessFileOps* ops_;  // not owned
  ModularRandomAccessFile(const ModularRandomAccessFile&) = delete;
  void operator=(const ModularRandomAccessFile&) = delete;
};

class ModularWritableFile final : public WritableFile {
 public: