apollo-client/src/main/java/com/ctrip/framework/apollo/internals/ConfigServiceLocator.java/ConfigServiceLocator/schedulePeriodicRefresh
class ConfigServiceLocator:  private void schedulePeriodicRefresh() {
    this.m_executorService.scheduleAtFixedRate(
        new Runnable() {
          @Override
          public void run() {
            logger.debug("refresh config services");
            Tracer.logEvent("Apollo.MetaService", "periodicRefresh");
            tryUpdateConfigServices();
          }
        }, m_configUtil.getRefreshInterval(), m_configUtil.getRefreshInterval(),
        m_configUtil.getRefreshIntervalTimeUnit());
  }