Adding items to Swift array across multiple threads causing issues (because arrays aren't thread safe) - how do I get around that?

Question

I want to add given blocks to an array, and then run all the blocks contained in the array, when requested. I have code similar to this:

class MyArrayBlockCl         


        

Answer 1

Details

• Xcode 10.1 (10B61)
• Swift 4.2

Solution

import Foundation

class AtomicArray {

    private lazy var semaphore = DispatchSemaphore(value: 1)
    private var array: [T]

    init (array: [T]) { self.array = array }

    func append(newElement: T) {
        wait(); defer { signal() }
        array.append(newElement)
    }

    subscript(index: Int) -> T {
        get {
            wait(); defer { signal() }
            return array[index]
        }
        set(newValue) {
            wait(); defer { signal() }
            array[index] = newValue
        }
    }

    var count: Int {
        wait(); defer { signal() }
        return array.count
    }

    private func wait() { semaphore.wait() }
    private func signal() { semaphore.signal() }

    func set(closure: (_ curentArray: [T])->([T]) ) {
        wait(); defer { signal() }
        array = closure(array)
    }

    func get(closure: (_ curentArray: [T])->()) {
        wait(); defer { signal() }
        closure(array)
    }

    func get() -> [T] {
        wait(); defer { signal() }
        return array
    }
}

extension AtomicArray: CustomStringConvertible {
    var description: String { return "\(get())"}
}

Usage

The basic idea is to use the syntax of a regular array

let atomicArray = AtomicArray(array: [3,2,1])

 print(atomicArray)
 atomicArray.append(newElement: 1)

 let arr = atomicArray.get()
 print(arr)
 atomicArray[2] = 0

 atomicArray.get { currentArray in
      print(currentArray)
 }

 atomicArray.set { currentArray -> [Int] in
      return currentArray.map{ item -> Int in
           return item*item
      }
 }
 print(atomicArray)

Usage result

Full sample

import UIKit

class ViewController: UIViewController {

    var atomicArray = AtomicArray(array: [Int](repeating: 0, count: 100))

    let dispatchGroup = DispatchGroup()

    override func viewDidLoad() {
        super.viewDidLoad()

        arrayInfo()

        sample { index, dispatch in
            self.atomicArray[index] += 1
        }

        dispatchGroup.notify(queue: .main) {
            self.arrayInfo()
            self.atomicArray.set { currentArray -> ([Int]) in
                return currentArray.map{ (item) -> Int in
                    return item + 100
                }
            }
           self.arrayInfo()
        }

    }

    private func arrayInfo() {
        print("Count: \(self.atomicArray.count)\nData: \(self.atomicArray)")
    }

    func sample(closure: @escaping (Int,DispatchQueue)->()) {

        print("----------------------------------------------\n")

        async(dispatch: .main, closure: closure)
        async(dispatch: .global(qos: .userInitiated), closure: closure)
        async(dispatch: .global(qos: .utility), closure: closure)
        async(dispatch: .global(qos: .default), closure: closure)
        async(dispatch: .global(qos: .userInteractive), closure: closure)
    }

    private func async(dispatch: DispatchQueue, closure: @escaping (Int,DispatchQueue)->()) {

        for index in 0..

Full sample result