code: private Iterator<ConcurrentServiceReferenceElement<T>> elements() {
          Collection<ConcurrentServiceReferenceElement<T>> set;
          synchronized (elementMap) {
              if (elementSetUnsorted) {
                  elementSet = new ConcurrentSkipListSet<ConcurrentServiceReferenceElement<T>>(elementMap.values());
                  elementSetUnsorted = false;
              }
              set = elementSet;
          }
  
          return set.iterator();
      }
docs: Return an iterator for the elements in service ranking order.