/// A list iterator pointing to the entry's position in the LRU list.
    std::list<std::string>::iterator lru_iterator;
  };

  bool LookupLocked(const std::string& key, T* value)
      ABSL_EXCLUSIVE_LOCKS_REQUIRED(mu_) {
    auto it = cache_.find(key);
    if (it == cache_.end()) {
      return false;
    }
    lru_list_.erase(it->second.lru_iterator);
    if (timer_seconds_() - it->second.timestamp > max_age_) {

                                      int64_t file_signature)
      ABSL_LOCKS_EXCLUDED(mu_);

  /// Remove all cached blocks for `filename`.
  void RemoveFile(const std::string& filename) ABSL_LOCKS_EXCLUDED(mu_);

  /// Remove all cached data.
  void Flush() ABSL_LOCKS_EXCLUDED(mu_);

  /// Accessors for cache parameters.
  size_t block_size() const { return block_size_; }

void RecordMutation(TF_Graph* graph, const TF_Operation& op,
                    const char* mutation_type)
    TF_EXCLUSIVE_LOCKS_REQUIRED(graph->mu);

bool ExtendSessionGraphHelper(TF_Session* session, TF_Status* status)
    TF_LOCKS_EXCLUDED(session->graph->mu, session->mu);

std::string getTF_OutputDebugString(TF_Output node);