// append an incremental tag to the prefix: "gradients_1/", "gradients_2/", ...
// See TF_AddGradientsWithPrefix, which provides a means to specify a custom
// name prefix for operations added to a graph to compute the gradients.
//
// WARNING: This function does not yet support all the gradients that python
// supports. See
// https://www.tensorflow.org/code/tensorflow/cc/gradients/README.md

  /// operations.
  ///
  /// This operation must be provided. See "REQUIRED OPERATIONS" above.
  void (*cleanup)(TF_ReadOnlyMemoryRegion* region);

  /// Returns a pointer to the memory region.
  ///
  /// This operation must be provided. See "REQUIRED OPERATIONS" above.
  const void* (*data)(const TF_ReadOnlyMemoryRegion* region);