apollo-core/src/main/java/com/ctrip/framework/foundation/Foundation.java/Foundation/getManager
class Foundation:  private static ProviderManager getManager() {
    try {
      if (s_manager == null) {
        // Double locking to make sure only one thread initializes ProviderManager.
        synchronized (lock) {
          if (s_manager == null) {
            s_manager = ServiceBootstrap.loadFirst(ProviderManager.class);
          }
        }
      }

      return s_manager;
    } catch (Throwable ex) {
      s_manager = new NullProviderManager();
      logger.error("Initialize ProviderManager failed.", ex);
      return s_manager;
    }
  }