void ConcurrentG1RefineThread::sample_young_list_rs_lengths() {

  {- -------------------------------------------
  (1) 
      ---------------------------------------- -}

      G1CollectedHeap* g1h = G1CollectedHeap::heap();
      G1CollectorPolicy* g1p = g1h->g1_policy();

  {- -------------------------------------------
  (1) 
      ---------------------------------------- -}

      if (g1p->adaptive_young_list_length()) {
        int regions_visited = 0;
        g1h->young_list()->rs_length_sampling_init();
        while (g1h->young_list()->rs_length_sampling_more()) {
          g1h->young_list()->rs_length_sampling_next();
          ++regions_visited;

          // we try to yield every time we visit 10 regions
          if (regions_visited == 10) {
            if (_sts.should_yield()) {
              _sts.yield("G1 refine");
              // we just abandon the iteration
              break;
            }
            regions_visited = 0;
          }
        }

        g1p->check_prediction_validity();
      }
    }