DispatchGroup Example, you can copy and paste this code to your swift playground to see it working.

DispatchGroupExample.swift

import Foundation

func doMultipleWork() {
    var items: [Int] = []
    let group = DispatchGroup()
    
    group.enter()
    doSomeWork(position: 1) {
        items.append(1)
        group.leave()
    }
    
    group.enter()
    doSomeWork(position: 2) {
        items.append(2)
        group.leave()
    }
    
    // When all work is done this gest called
    group.notify(queue: .main) {
        print(String(describing: items))
    }
}

func doSomeWork(position: Int, completion: () -> Void) {
    completion()
}

doMultipleWork()