code: public void addListArgumentSlots(Slot initialSlot, List<Slot> slotList) {
      if (!initialSlot.isFilled()) {
        throw new IllegalArgumentException("initialSlot must be filled");
      }
      verifyStateBeforAdd(initialSlot);
      int groupSize = slotList.size() + 1;
      addSlotDescriptor(new SlotDescriptor(initialSlot, groupSize));
      for (Slot slot : slotList) {
        addSlotDescriptor(new SlotDescriptor(slot, groupSize));
      }
    }
docs: Adds multiple slots to this barrier's waiting-on list representing a single
  Job argument of type list.
  
  @param slotList A list of slots that will be added to the barrier and used
  as the elements of the list Job argument.
  @throws IllegalArgumentException if intialSlot is not filled.