log.debug("Removing expired " + links.map);
            }
            roots.remove(root);
            links = null;
        }

        if ( links == null ) {
            log.trace("Loadings roots");
            String refServerName = domain;
            dr = fetchRootReferral(tf, domain, root, refServerName);
            links = cacheRootReferral(tf, domain, root, roots, dr, links);
        }

      } finally {
        monitor.leave();
      }
      return builder.build();
    }

    ImmutableMap<Service, Long> startupTimes() {
      List<Entry<Service, Long>> loadTimes;
      monitor.enter();
      try {
        loadTimes = Lists.newArrayListWithCapacity(startupTimers.size());
        // N.B. There will only be an entry in the map if the service has started