code: @FFDCIgnore(IndexOutOfBoundsException.class)
      private boolean ensureElement(int index) {
          try {
              get(index);
              return true;
          } catch (IndexOutOfBoundsException e) {
              return false;
          }
      }
docs: Blocking call to ensure an element is available
  
  @return false if the element is unavailable and the list has timed out