I have a problem with the `sleep` function in Swift code. I'm using `import Darwin` and `usleep(400000)`. Some actions before reaching the sleep are blocked and I dont know why. Here a short example from my code:

```
@IBAction func Antwort4Button(_ sender: Any) {
    if (richtigeAntwort == "4"){
        Antwort4.backgroundColor = UIColor.green
        Ende.text = "Richtig!"

        NaechsteFrage()
    }
    else {
        Ende.text = "Falsch!"

        //NaechsteFrage()
    }
}

func NaechsteFrage() {
    usleep(400000)

    Antwort1.backgroundColor = UIColor.red
    Antwort2.backgroundColor = UIColor.red
    Antwort3.backgroundColor = UIColor.red
    Antwort4.backgroundColor = UIColor.red

    Ende.text = ""

    FragenSammlung()
}

```

This lines will be not executed:

```
Antwort4.backgroundColor = UIColor.green

Ende.text = "Richtig!"

```

Why is calling sleep blocking these actions? If I delete the `import Darwin` and the `sleep`, my code works fine. Has anyone an idea? Sorry for my bad english :P