// The keys of this map are all the active sessions using this graph. Each
  // value records whether the graph has been mutated since the corresponding
  // session has been run (this is detected in RecordMutation function). If the
  // string is empty, no mutation has occurred. Otherwise the string is a
  // description of the mutation suitable for returning to the user.
  //

  mutex_lock l(graph->mu);
  op->node.AddAttr(attr_name, attr_val);
  RecordMutation(graph, *op, "setting attribute");
}

void TF_ClearAttr(TF_Graph* graph, TF_Operation* op, const char* attr_name,
                  TF_Status* status) {
  using tensorflow::RecordMutation;
  mutex_lock l(graph->mu);
  op->node.ClearAttr(attr_name);
  RecordMutation(graph, *op, "clearing attribute");
}