iOS Concurrency with GCD & Operations, Episode 19: Challenge: Download Images in OperationQueue | Kodeco

🎓 Courses & Articles
1
This is a companion discussion topic for the original entry at https://www.kodeco.com/38462287-ios-concurrency-with-gcd-operations/lessons/19
2

Hi! Regarding your solution of the challenge, I am wondering why you are not appending the downloaded images using a serial queue so only one operation at a time can modify the array.
shouldn’t be like that since the operation queue for downloading is concurrent?

Your code is:

op.completionBlock = {
  if let image = op.image { images.append(image) }
}

and I suppose ideally it should be:

op.completionBlock = {
        if let image = op.image {
            imagesQueue.addOperation {
                images.append(image)
            }
        }
    }
3

hi Jorge! sorry for the delay. You’re quite right, you should use a serial queue in an app. I should have mentioned it. In a playground, which runs on the main thread, it works without the serial queue.

4

Thank you for your reply! :smiley: