(PHP 5 >= 5.4.0, PHP 7)
SessionHandlerInterface::gc — Cleanup old sessions
$maxlifetime
   ) : intCleans up expired sessions. Called by session_start(), based on session.gc_divisor, session.gc_probability and session.gc_maxlifetime settings.
maxlifetime
      Sessions that have not updated for the last maxlifetime seconds will be removed.
     
会话存储的返回值(通常成功返回 0,失败返回 1)。