// be an empty string if no device was explicitly requested, but will
  // otherwise be the name of this custom device. Ops are placed onto a custom
  // device if any of their inputs are on that custom device, but custom devices
  // are free to set a bad status in order to require explicit placement.
  void (*execute)(const TFE_Op* op, int* num_outputs,

  virtual ImmediateExecutionContext* GetContext() const = 0;

  // Following two methods are used to support custom device.
  // Return true if the inputs contain custom device tensor handle. It means
  // that the argument need to be handled by a custom device.
  virtual bool HasCustomDeviceInput() const = 0;

  virtual const tensorflow::OpDef* OpDef() const = 0;

// Creates a new operation - see `TF_NewOperation` for more details.
//
// The lock for `graph` must be held when calling this function.
//
// Unless implementing advanced behavior, like custom gradient functions, you
// most likely need to call `TF_NewOperation` instead.
TF_CAPI_EXPORT extern TF_OperationDescription* TF_NewOperationLocked(
    TF_Graph* graph, const char* op_type, const char* oper_name);

  // Experimental Custom Device.
  //===--------------------------------------------------------------------===//
  virtual CustomDeviceOpHandler& GetCustomDeviceOpHandler() = 0;

  // Returns whether `device_name` is registered as a custom device.
  virtual bool IsCustomDevice(const string& device_name) = 0;

  // Register a custom device. It will return error is the device name is