apollo-core/src/main/java/com/ctrip/framework/apollo/core/MetaDomainConsts.java/MetaDomainConsts/selectMetaServerAddress
class MetaDomainConsts:  private static String selectMetaServerAddress(String metaServerAddresses) {
    String metaAddressSelected = selectedMetaServerAddressCache.get(metaServerAddresses);
    if (metaAddressSelected == null) {
      // initialize
      if (periodicRefreshStarted.compareAndSet(false, true)) {
        schedulePeriodicRefresh();
      }
      updateMetaServerAddresses(metaServerAddresses);
      metaAddressSelected = selectedMetaServerAddressCache.get(metaServerAddresses);
    }

    return metaAddressSelected;
  }