if (g == nullptr) return;
  g->mu.lock();
  g->delete_requested = true;
  const bool del = g->sessions.empty();
  g->mu.unlock();
  if (del) delete g;
}

TF_Operation* TF_GraphOperationByName(TF_Graph* graph, const char* oper_name) {
  mutex_lock l(graph->mu);
  auto iter = graph->name_map.find(oper_name);
  if (iter == graph->name_map.end()) {
    return nullptr;
  } else {