std::unique_ptr<ReadOnlyMemoryRegion>* result) override;
  Status FileExists(const std::string& fname, TransactionToken* token) override;
  bool FilesExist(const std::vector<std::string>& files,
                  TransactionToken* token,
                  std::vector<Status>* status) override;
  Status GetChildren(const std::string& dir, TransactionToken* token,

  ///
  /// On successful deletion, `status` must be `TF_OK` and `*undeleted_files`
  /// and `*undeleted_dirs` must be 0. On unsuccessful deletion, `status` must
  /// be set to the reason why one entry couldn't be removed and the proper
  /// count must be updated. If the deletion is unsuccessful because the
  /// traversal couldn't start, `*undeleted_files` must be set to 0 and
  /// `*undeleted_dirs` must be set to 1.
  ///

//
// A TensorHandle is management class around a Tensor which may track additional
// metadata and synchronization.
//
// This allows us to hide concrete implementations of TensorHandle from header
// files. The interface lists the common functionality that must be provided by
// any concrete implementation. However, in cases where the true concrete class
// is needed a static_cast can be applied.