PHP 将session写入到memcached

<?php
class MemcacheSession
{
    // memcache对象
    private static $handler = null;
    // 过期时间 秒
    private static $lifetime = null;
    // 当前时间
    private static $time = null;
    // session名前缀
    private const NS = 'session_';

    // 初始化
    private static function init($handler)
    {
        self::$handler = $handler;
        self::$lifetime = 1440;
        self::$time = time();
    }

    // 外部调用初始化
    public static function start(Memcached $memcached)
    {
        self::init($memcached);

        // 自定义session存储介质
        session_set_save_handler(
            array(__CLASS__, 'open'),
            array(__CLASS__, 'close'),
            array(__CLASS__, 'read'),
            array(__CLASS__, 'write'),
            array(__CLASS__, 'destroy'),
            array(__CLASS__, 'gc')
        );
        if (!headers_sent() && session_id() == '') session_start();
    }

    public static function open($path, $name)
    {
        return true;
    }

    public static function close()
    {
        return true;
    }

    public static function read($PHPSESSID)
    {
        $out = self::$handler->get(self::session_key($PHPSESSID));

        if ($out === false || $out == null) return '';
        return $out;
    }

    public static function write($PHPSESSID, $data)
    {
        return self::$handler->set(self::session_key($PHPSESSID), $data, self::$lifetime);
    }

    public static function destroy($PHPSESSID)
    {
        return self::$handler->delete(self::session_key($PHPSESSID));
    }

    public static function gc($lifetime)
    {
        return true;
    }

    private static function session_key($PHPSESSID)
    {
        $session_key = self::NS . $PHPSESSID;
        return $session_key;
    }
}

$memcached = new Memcached();
$memcached->addServer('127.0.0.1', 11211);
MemcacheSession::start($memcached);

// 写
$_SESSION['aaa'] = '你好世界';
// 读
var_dump($_SESSION);