code: void cancelTasklet(final int taskletId) {
      final TaskletCancellationRequest cancellationRequest = new TaskletCancellationRequest(taskletId);
      vortexRequestor.sendAsync(reefTask, cancellationRequest);
    }
docs: Sends a request to cancel a Tasklet on a {@link org.apache.reef.vortex.evaluator.VortexWorker}.