code: @Private
    @Override
    public void completed(final int pTaskletId, final TOutput result) {
      assert taskletId == pTaskletId;
      this.userResult = Optional.ofNullable(result);
      if (callbackHandler != null) {
        executor.execute(new Runnable() {
          @Override
          public void run() {
            callbackHandler.onSuccess(userResult.get());
          }
        });
      }
      this.countDownLatch.countDown();
    }
docs: Called by VortexMaster to let the user know that the Tasklet completed.