threading.swift

import UIKit

class ViewController: UIViewController {
    
    
    @IBOutlet weak var counterLabel: UILabel!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        DispatchQueue.global(qos: .userInteractive).async {
            let result = self.countTo(number: 1000)
            DispatchQueue.main.async {
                self.counterLabel.text = "\(result)"
            }
        
        }
        
    }
    
    func countTo(number: Int) -> Int {
        var counter = 0
        
        while counter < number {
            counter += 1
            print(counter)
        }
        
        return counter
    }
    
}