present UIAlertController while a presentation is in progress - swift

Question

I'm trying to display two different alerts immediately after each other. The first one is a loading indicator. The second one is an alert that tell the user if what they were doing has succeeded or not following a UDP message. I have simplified the code for presentation purposes.
My problem is that although I'm dismissing the loadingAlert before I call my second alert I still get an error:
Warning: Attempt to present UIAlertController on ViewController while a presentation is in progress!
My second alert is never shown.
Here is my Swift 4 code:
func getUpdate()
{
let loading = alert(title: "Performing Task...")
DispatchQueue.global(qos: .userInitiated).async {
let server:UDPServer=UDPServer(address:"0.0.0.0", port:5006)
let (data,_,_) = server.recv(1024)
DispatchQueue.main.async
{
loading.dismiss(animated: false, completion: nil)
OperationQueue.main.addOperation
{
alert(title: "How can I show this alert?")
}
}
}
}
func alert(title:String) -> UIAlertController
{
let alertController = UIAlertController(title: title, message: "", preferredStyle: UIAlertControllerStyle.alert)
...
rootViewController?.present(alertController, animated: true, completion: nil)
return alertController
}
What would be the best way of doing this?

Answer 1

Make use of the completion parameter in the call to dismiss:
DispatchQueue.main.async{
loading.dismiss(animated: false) {
OperationQueue.main.addOperation {
alert(title: "How can I show this alert?")
}
}
}