code: public function regenerateID($deleteOldSession = false)
      {
          if ($this->getIsActive()) {
              // add @ to inhibit possible warning due to race condition
              // https://github.com/yiisoft/yii2/pull/1812
              if (YII_DEBUG && !headers_sent()) {
                  session_regenerate_id($deleteOldSession);
              } else {
                  @session_regenerate_id($deleteOldSession);
              }
          }
      }
docs: Updates the current session ID with a newly generated one.
  
  Please refer to <https://secure.php.net/session_regenerate_id> for more details.
  
  This method has no effect when session is not [[getIsActive()|active]].
  Make sure to call [[open()]] before calling it.
  
  @param bool $deleteOldSession Whether to delete the old associated session file or not.
  @see open()
  @see isActive