self in dispatch queue doesn't cause retain cycle

DispatchQueueAsyncTaskRetainCycle.swift

import UIKit

class ListViewController: UIViewController {
    let label = UILabel(frame: CGRect(x: 100, y: 200, width: 300, height: 50))

    override func viewDidLoad() {
        super.viewDidLoad()

        view.backgroundColor = .white

        label.text = "Animating"
        view.addSubview(label)
        let controller = DetailViewController()
        controller.definesPresentationContext = true

        let navControll = UINavigationController(rootViewController: controller)
        self.navigationController?.present(navControll, animated: true, completion: nil)
    }
    
    deinit {
        print("List controller Deinit")
    }
}

class DetailViewController: UIViewController {
    var listTitle: (() -> String)?

    override func viewDidLoad() {
        super.viewDidLoad()
        
        performAsyncTaskIntoConcurrentQueue(with: {
            print("\n############")
            print("###### All images are downloaded")
        })
    }
    
    func performAsyncTaskIntoConcurrentQueue(with completion: @escaping () -> ()) {
        let queue = DispatchQueue(label: "com.queue.Concurrent", attributes: .concurrent)
        let group = DispatchGroup()
        for i in 1...5 {
            group.enter()
            queue.async {
                let imageURL = URL(string: "https://upload.wikimedia.org/wikipedia/commons/0/07/Huge_ball_at_Vilnius_center.jpg")!
                let _ = try! Data(contentsOf: imageURL)
                print(self.view.description)
                print("###### Image \(i) Downloaded ######")
                group.leave()
            }
        }
        group.notify(queue: DispatchQueue.main) {
            completion()
        }
    }
    
    deinit {
        print("Detail controller got deallocated")
    }
}