code: @Override
      @SuppressWarnings({ "unchecked", "SuspiciousToArrayCall" })
      public void close() {
          final AddressResolver<T>[] rArray;
          synchronized (resolvers) {
              rArray = (AddressResolver<T>[]) resolvers.values().toArray(new AddressResolver[0]);
              resolvers.clear();
          }
  
          for (AddressResolver<T> r: rArray) {
              try {
                  r.close();
              } catch (Throwable t) {
                  logger.warn("Failed to close a resolver:", t);
              }
          }
      }
docs: Closes all {@link NameResolver}s created by this group.