Delayed actions doubling up after 10 loops. Why Is this happening and how do I make it stop?

Question

I have a for loop running to print out a number from an array. I am using a delay function to spread the printing of the numbers by a half second each time. For the first 10 loops it works perfectly and there is a half second between each printed number.

After 10 loops of it functioning perfect it will start printing 2 numbers at a time, after 20 loops it will print 3 at a time. This is not what I am intending and I am not sure why it is doing this.

Here is the loop and the delay function. timer is set to 0.5 prior to the loop running.

for i in 1...30 {         
    delay(timer) {    
        print("Button \(self.newLevel[i-1].areaNumber) was lit up")
    }

    timer += 0.5
}

func delay(_ delay:Double, closure:@escaping ()->()) {
    DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + Double(Int64(delay * Double(NSEC_PER_SEC))) / Double(NSEC_PER_SEC), execute: closure)
}

Thank you for your time/help.

Answer 1

Not sure on the actual resolution to the question about why it behaves like this but I used a timer with a counter to trigger invalidate as suggested and it works perfectly as a solution.

Thanks again.