*/
    void onError(String phase, String error);

    /**
     * Returns a no-op callback implementation.
     *
     * @return a callback that does nothing
     */
    static ChatPhaseCallback noOp() {
        return new ChatPhaseCallback() {
            @Override
            public void onPhaseStart(final String phase, final String message) {
                // no-op
            }

            @Override

    @Override
    protected void doStart() {
      notifyStarted();
    }

    @Override
    protected void doStop() {
      notifyStopped();
    }
  }

  /*
   * A NoOp service that will delay the startup and shutdown notification for a configurable amount
   * of time.
   */
  private static class NoOpDelayedService extends NoOpService {
    private final long delay;

      from both the node defs and the function defs of the graph. Note that
      this currently only strips the `Assert` nodes from the graph and
      converts them into `NoOp`s instead.

*   `tf.data`

    * `tf.data` now has an `autotune_options.initial_parallelism` option to
      control the initial parallelism setting used by autotune before the data