PHP单例模式

class siagle{
	public $hash = '';
	static protected $ins = NULL;
	final protected function __construct(){
		$this->hash = mt_rand(1,9999);
	}
	static public function getInstence(){
		if (self::$ins instanceof self){
			return self::$ins;
		}
		self::$ins = new self();
		return self::$ins;
	}
}

$s1 = siagle::getInstence();
$s2 = siagle::getInstence();
echo $s1 == $s2 ? '相等':'不相等';