Synchronous UI operation

Synchronous UI operation

I am creating custom alertview in which I wish to integrate synchronous
operation. that is before dismissing first alert second one should not
show. To create this i am customizing this downloaded control. Here
UIViewController used as subclass to show an alert, we need to present to
above view controller to show alert.
Code
[alert show];
[alert show];
[alert show];
In show method I present to alert view subclass. When I consecutively call
the show method, the operation should perform synchronously. The second
alert should not pop up until the first one is dismissed.
Can you please provide the best approach to achieve this.