code: public static function getGlobalRequestId()
      {
          if (!self::$_requestId) {
              try {
                  if (isset($_GET[self::LOG_REQUEST_ID]) && $_GET[self::LOG_REQUEST_ID]) {
                      self::$_requestId = $_GET[self::LOG_REQUEST_ID];
                  } else if (isset($_POST[self::LOG_REQUEST_ID]) && $_POST[self::LOG_REQUEST_ID]) {
                      self::$_requestId = $_POST[self::LOG_REQUEST_ID];
                  } else {
                      self::$_requestId = uniqid();
                  }
              } catch (Exception $e) {
                  self::$_requestId = uniqid();
              }
          }
          return self::$_requestId;
      }
docs: 获取全局唯一请求id.
  如果未设置则从$_GET、$_POST参数中区搜索.
  如果还未找到则直接创建.
  
  @return string