public static function flush() {
    if (isset(self::$app_log_group)) {
      $req = new FlushRequest();
      $req->setLogs(self::$app_log_group->serializeToString());
      $resp = new VoidProto();
      ApiProxy::makeSyncCall('logservice', 'Flush', $req, $resp);
      self::$app_log_group->clear();
      self::$last_flush_time = microtime(true);
    }
  }