semaphore-swift

semaphore.swift

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

import UIKit



class ViewController: UIViewController {
// Create 4 iamge views in the storyboard and connect them to this object.
  @IBOutlet var imgs: [UIImageView]!
  override func viewDidLoad() {
    super.viewDidLoad()
    
//    imgs.forEach { i in
//      i.removeFromSuperview()
//    }
    
    for index in 0...1000 {
      queue.async {
          semaphore.wait()
          
//          defer {
//              semaphore.signal()
//          }
          
        let t = "https://dummyimage.com/5120x1000/000000/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...3)]
              i.image = image
              
            }
            
          }
        }.resume()
        
        
      }
    }
  }
}


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

let queue = DispatchQueue.global(qos: .background)
let semaphore = DispatchSemaphore(value: 1)