this.callback = callback;
    }

    @Override
    public void run() {
      if (future instanceof InternalFutureFailureAccess) {
        Throwable failure =
            InternalFutures.tryInternalFastPathGetFailure((InternalFutureFailureAccess) future);
        if (failure != null) {
          callback.onFailure(failure);
          return;
        }
      }
      V value;
      try {