code: public static synchronized LoadBalancerRegistry getDefaultRegistry() {
      if (instance == null) {
        List<LoadBalancerProvider> providerList = ServiceProviders.loadAll(
            LoadBalancerProvider.class,
            HARDCODED_CLASSES,
            LoadBalancerProvider.class.getClassLoader(),
            new LoadBalancerPriorityAccessor());
        instance = new LoadBalancerRegistry();
        for (LoadBalancerProvider provider : providerList) {
          logger.fine("Service loader found " + provider);
          if (provider.isAvailable()) {
            instance.addProvider(provider);
          }
        }
        instance.refreshProviderMap();
      }
      return instance;
    }
docs: Returns the default registry that loads providers via the Java service loader mechanism.