code: @Private
    @Override
    public void threwException(final int pTaskletId, final Exception exception) {
      assert taskletId == pTaskletId;
  
      this.userException = exception;
      if (callbackHandler != null) {
        executor.execute(new Runnable() {
          @Override
          public void run() {
            callbackHandler.onFailure(exception);
          }
        });
      }
      this.countDownLatch.countDown();
    }
docs: Called by VortexMaster to let the user know that the Tasklet threw an exception.