php——数据库连接的伪单例模式代码

各位redis群的同学，帮忙查看指正一下代码，多谢了，希望看到各位的改进意见

<?phpclass Singleton{// MYSQL数据库连接信息const MYSQLHOSTNAME = "127.0.0.1";const MYSQLCHARSET = "utf8";private static $instances = array(); //伪类单例private $db; //数据库连接句柄/** * Description:私有化构造函数，防止外界实例化对象 */private function __construct($dbname, $username, $password){//连接数据库$this->db = new mysqli(self::MYSQLHOSTNAME, $username, $password, $dbname);$this->db->set_charset(self::MYSQLCHARSET);if (mysqli_connect_errno()){throw new CircleMysqlException("error", 1000);}}/** * Description:私有化克隆函数，防止外界克隆对象 */private function __clone(){}/** * Description:静态方法，单例访问统一入口 * @return Singleton：返回应用中的唯一对象实例 */public static function GetInstance($dbname, $username, $password){$hash = (string) $dbname;if (!isset(self::$instances[$hash])){self::$instances[$hash] = new self($dbname, $username, $password);}return self::$instances[$hash];}/** * Description:获取数据库的私有方法的连接句柄 */public function GetDbConnect(){return $this->db;}/** * Description:关闭数据库链接的方法 */public function CloseDbConnect($dbname){$hash = (string) $dbname;self::$instances[$hash]->db->close();unset(self::$instances[$hash]);}}