TF_Buffer* value_buf,
                                                 TF_Status* status);

// Delete configuration key-value. If `key` is a directory, recursively clean up
// all key-values under the path specified by `key`.
TF_CAPI_EXPORT extern void TFE_DeleteConfigKeyValue(TFE_Context* ctx,
                                                    const char* key,

                     TF_Status* status);

  /// Creates the directory specified by `path` and all needed ancestors.
  ///
  /// Plugins:
  ///   * Must set `status` to `TF_OK` if directory was created.
  ///   * Must set `status` to `TF_FAILED_PRECONDITION` if `path` is invalid or
  ///     if it exists but is not a directory.
  ///   * Might use any other error value for `status` to signal other errors.
  ///

  // Release any underlying resources, including the interface object.
  //
  // WARNING: The destructor of this class is marked as protected to disallow
  // clients from directly destroying this object since it may manage its own
  // lifetime through ref counting. Thus clients MUST call Release() in order to
  // destroy an instance of this class.
  virtual void Release() = 0;

// returned TF_WhileParams is not valid, and the caller should not call
// TF_FinishWhile() or TF_AbortWhile().
//
// Missing functionality (TODO):
// - Gradients
// - Reference-type inputs
// - Directly referencing external tensors from the cond/body graphs (this is
//   possible in the Python API)
TF_CAPI_EXPORT extern TF_WhileParams TF_NewWhile(TF_Graph* g, TF_Output* inputs,

  std::function<void(BackwardFunction*)> backward_function_deleter;
};

// Map from tensor_id to internally-defined operation-id of the operation which
// produced this tensor. A value of -1 means that the tensor was directly
// watched and not the result of any operation in the tape.
using TensorTape = std::unordered_map<int64_t, int64_t>;

// Map from operation-id to tape entry.
template <typename BackwardFunction, typename TapeTensor>

  // Release any underlying resources, including the interface object.
  //
  // WARNING: The destructor of this class is marked as protected to disallow
  // clients from directly destroying this object since it may manage it's own
  // lifetime through ref counting. Thus this must be allocated on the heap and
  // clients MUST call Release() in order to destroy an instance of this class.

  // Register a custom device. It will return error is the device name is
  // already registered.
  // TODO(tfrt-devs): Remove this method. Let caller register it directly into
  // CustomDeviceOpHandler.
  virtual Status RegisterCustomDevice(const string& name,
                                      std::unique_ptr<CustomDevice> device) = 0;

  Status CreateDir(const std::string& dirname,
                   TransactionToken* token) override;
  Status Stat(const std::string& fname, TransactionToken* token,
              FileStatistics* stat) override;
  Status IsDirectory(const std::string& fname,
                     TransactionToken* token) override;
  Status GetFileSize(const std::string& fname, TransactionToken* token,
                     uint64* file_size) override;