func queuing() {
    var concurrentQueue = DispatchQueue(label: "test",attributes: .concurrent)
    var myGroup = DispatchGroup()
    var mySecondGroup = DispatchGroup()

    myGroup.enter()
    mySecondGroup.enter()

    concurrentQueue.async {
        for i in 0...5 {
            print(i)
            if (i==5) {
                myGroup.leave()
            }
        }
    }

    myGroup.notify(queue: DispatchQueue.main) {
        print("Initial Json request with List of URLs completed")
        concurrentQueue.async {
            for i in 10...15 {
                print(i)
                if (i==15){
                    mySecondGroup.leave()
                }
            }
        }
    }

    mySecondGroup.notify(queue: DispatchQueue.main) {
        print("All Images download complete")
    }
}

queuing()