code: private function _mCall(&$pCall) {
          if (!isset($pCall[self::_MIDDLEWARE]))
              return;
          $is_last = yield;
          foreach ($pCall[self::_MIDDLEWARE] as $callback) {
              if ($this->_delayed) {
                  $this->_delayed = false;
                  yield;
              }
              if (!($callback($is_last) ?? true))
                  break;
          }
          $this->_delayed = false;
      }
docs: 将中间件回调封装到生成器中待调用
  
  @param $pCall
  @return \Generator