semaphore+dispatchGroup+swift

semaphore-dispatchgroup.swift

//
//  ViewController.swift
//  semap
//
//  Created by Glenn Posadas on 5/10/22.
//

import UIKit

class ViewController: UIViewController {
  
  @IBOutlet var imgs: [UIImageView]!
  
  override func viewDidLoad() {
    super.viewDidLoad()
    
    print("Batch one")
    
    // BATCH ONE - first two imageviews
    
    queue1.async(group: g) {
      for index in 0...100 {
        semaphore.wait()

        let t = "https://dummyimage.com/500x600/000000/fff&text=" + "\(index)"
        let url = URL(string: t)!
        
        URLSession.shared.dataTask(with: url) { [weak self] data, resp, err in
          guard let self = self else { return }
          if let data = data,
             let image = UIImage(data: data) {
            
            DispatchQueue.main.async {
              semaphore.signal()
              
              
              let i = self.imgs[Int.random(in: 0...1)]
              i.image = image
              
            }
            
          }
        }.resume()
      }
    }


    
    /// ----
    
    g.notify(queue: .main) {
      
      print("GROUP 1 is done ----- ✅")
      
      self.startSecondBatch()
    }
    
  }
  
  func startSecondBatch() {
    
    queue2.async(group: g2) {
      print("START BATCH 222222")
      for index in 0...50 {
        semaphore.wait()
        let t = "https://dummyimage.com/500x600/232ca6/fff&text=" + "\(index)"
        let url = URL(string: t)!
        
        URLSession.shared.dataTask(with: url) { [weak self] data, resp, err in
          guard let self = self else { return }
          if let data = data,
             let image = UIImage(data: data) {
            
            DispatchQueue.main.async {
              semaphore.signal()
              
              
              let i = self.imgs[Int.random(in: 2...3)]
              i.image = image
              
            }
            
          }
        }.resume()

      }
    }
    
    /// ----
    
    g2.notify(queue: .main) {
      
      print("GROUP 222222 is done ----- ✅")
      
      self.startSecondBatch()
    }
  }
}


let url = URL(string: "https://source.unsplash.com/random/5120x1000")!

let queue1 = DispatchQueue.global(qos: .background)
let queue2 = DispatchQueue.global(qos: .background)
let semaphore = DispatchSemaphore(value: 4)
let g = DispatchGroup()
let g2 = DispatchGroup()