Basics of QoS - Swift - GCD

QoSGCD.swift

import Foundation
import PlaygroundSupport
PlaygroundPage.current.needsIndefiniteExecution = true

extension Date {
    var currentTimeStamp: Int64 {
        Int64(self.timeIntervalSince1970 * 1000)
    }
}
func concurrency() {
    print("background start Time: \(Date().currentTimeStamp) ")
    DispatchQueue.global(qos: .background).async {
        for i in 1...3{
            sleep(3)
            print("background Counter:\(i), time \(Date().currentTimeStamp) ")
        }
    } 
    print("UserInitiated start Time: \(Date().currentTimeStamp) ")
    DispatchQueue.global(qos: .userInitiated).async {
        for i in 1...3{
            sleep(3)
            print("UserInitiated Counter:\(i), time \(Date().currentTimeStamp) ")
        }
    } 
    print("Utility start Time: \(Date().currentTimeStamp) ")
    DispatchQueue.global(qos: .utility).async {
        for i in 1...3{
            sleep(3)
            print("Utility Counter:\(i), time \(Date().currentTimeStamp) ")
        }
    } 
    
    print("UserInteractive start Time: \(Date().currentTimeStamp) ")
    DispatchQueue.global(qos: .userInteractive).async {
        for i in 1...3{
            sleep(3)
            print("UserInteractive Counter:\(i), time \(Date().currentTimeStamp) ")
        }
    } 
    print("Default start Time: \(Date().currentTimeStamp) ")
    DispatchQueue.global(qos: .default).async {
        for i in 1...3{
            sleep(3)
            print("Default Counter:\(i), time \(Date().currentTimeStamp) ")
        }
    } 
}
concurrency()