code: private synchronized VortexFutureDelegate fetchDelegate(final List<Integer> taskletIds) {
      VortexFutureDelegate delegate = null;
      for (final int taskletId : taskletIds) {
        final VortexFutureDelegate currDelegate = taskletFutureMap.remove(taskletId);
        if (currDelegate == null) {
          // TODO[JIRA REEF-500]: Consider duplicate tasklets.
          throw new RuntimeException("Tasklet should only be removed once.");
        }
  
        if (delegate == null) {
          delegate = currDelegate;
        } else {
          assert delegate == currDelegate;
        }
      }
  
      return delegate;
    }
docs: Fetches a delegate that maps to the list of Tasklets.