void FlushAllListeners();

XlaActivityListenerList* GetXlaActivityListenerList() {
  static XlaActivityListenerList* listener_list = new XlaActivityListenerList;
  static int unused = std::atexit(FlushAllListeners);
  (void)unused;
  return listener_list;
}

template <typename FnTy>
Status ForEachListener(FnTy fn) {
  XlaActivityListenerList* listener_list = GetXlaActivityListenerList();