Sprintf, эквивалентный в Java

Подробности

Xcode 9.2, Swift 4

Решение

class AsyncOperation {

    typealias NumberOfPendingActions = Int
    typealias DispatchQueueOfReturningValue = DispatchQueue
    typealias CompleteClosure = ()->()

    private let dispatchQueue: DispatchQueue
    private var semaphore: DispatchSemaphore

    private var numberOfPendingActionsQueue: DispatchQueue
    public private(set) var numberOfPendingActions = 0

    var whenCompleteAll: (()->())?

    init(numberOfSimultaneousActions: Int, dispatchQueueLabel: String) {
        dispatchQueue = DispatchQueue(label: dispatchQueueLabel)
        semaphore = DispatchSemaphore(value: numberOfSimultaneousActions)
        numberOfPendingActionsQueue = DispatchQueue(label: dispatchQueueLabel + "_numberOfPendingActionsQueue")
    }

    func run(closure: @escaping (@escaping CompleteClosure)->()) {

        self.numberOfPendingActionsQueue.sync {
            self.numberOfPendingActions += 1
        }

        dispatchQueue.async {
            self.semaphore.wait()
            closure {
                self.numberOfPendingActionsQueue.sync {
                    self.numberOfPendingActions -= 1
                    if self.numberOfPendingActions == 0 {
                        self.whenCompleteAll?()
                    }
                }
                self.semaphore.signal()
            }
        }
    }
}

Использование

let asyncOperation = AsyncOperation(numberOfSimultaneousActions: 1, dispatchQueueLabel: "AnyString")
asyncOperation.whenCompleteAll = {
    print("All Done")
}
for i in 0...5 {
    print("\(i)")
    asyncOperation.run{ completeClosure in
        // add any (sync/async) code
        //..

        // Make signal that this closure finished
        completeClosure()
    }
}

Полный образец

import UIKit

class ViewController: UIViewController {

    let asyncOperation = AsyncOperation(numberOfSimultaneousActions: 3, dispatchQueueLabel: "AnyString")
    let button = UIButton(frame: CGRect(x: 50, y: 80, width: 100, height: 40))
    let label = UILabel(frame: CGRect(x: 180, y: 50, width: 150, height: 100))

    var counter = 1
    var labelCounter = 0

    override func viewDidLoad() {
        super.viewDidLoad()

        button.setTitle("Button", for: .normal)
        button.setTitleColor(.blue, for: .normal)
        button.addTarget(self, action: #selector(buttonTapped), for: .touchUpInside)
        label.text = "\(labelCounter)"
        label.numberOfLines = 2
        label.textAlignment = .natural
        view.addSubview(button)
        view.addSubview(label)
    }

    @objc func buttonTapped() {
        //sample1()
        sample2()
    }

    func sample1() {
        print("Sample 1")
        labelCounter += 1
        label.text = "button tapped \(labelCounter) times"

        print("Button tapped at: \(Date())")
        asyncOperation.whenCompleteAll = {
            print("All Done")
        }
        asyncOperation.run{ completeClosure in
            let counter = self.counter
            print("     - Loading action \(counter) strat at \(Date())")
            self.counter += 1

            DispatchQueue.global(qos: .background).async {
                sleep(1)
                print("     - Loading action \(counter) end at \(Date())")
                completeClosure()
            }
        }
    }

    func sample2() {
        print("Sample 2")
        label.text = ""
        asyncOperation.whenCompleteAll = {
            print("All Done")
        }

        for i in 0...5 {
            asyncOperation.run{ completeClosure in
                let counter = self.counter
                print("     - Loading action \(counter) strat at \(Date())")
                self.counter += 1

                DispatchQueue.global(qos: .background).async {
                    sleep(UInt32(i+i))
                    print("     - Loading action \(counter) end at \(Date())")
                    completeClosure()
                }
            }
        }

    }
}

Результаты

Образец 1

Образец 2