I have been trying to work with the image downloader code provided in the session to see if I could download two images at once and cache them in the actor.
For some reason, when I enter the download method on the actor with two consecutive async let calls, the app hangs at the deepest suspension point.
I am providing a very minimum code you can copy and paste into a new iOS Storyboard-based project, replacing the code in ViewController.swift:
enum ImageDownloadError: Error {
case badImage
}
actor ImageDownloader {
private var cache: [URL: UIImage] = [:]
func image(from url: URL) async throws -> UIImage {
if let image = cache[url] {
return image
}
print("Downloading image")
let image = try await downloadImage(url: url)
print("Downloaded image")
cache[url] = image
return image
}
private func downloadImage(url: URL) async throws -> UIImage {
let imageRequest = URLRequest(url: url)
let (data, imageResponse) = try await URLSession.shared.data(for: imageRequest)
guard let image = UIImage(data: data), (imageResponse as? HTTPURLResponse)?.statusCode == 200 else {
throw ImageDownloadError.badImage
}
return image
}
}
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
async {
await downloadImages()
}
}
func downloadImages() async {
let downloader = ImageDownloader()
let imageURL = URL(string: "https://www.andyibanez.com/fairesepages.github.io/tutorials/async-await/part3/3.png")!
async let downloadedImage = downloader.image(from: imageURL)
//async let sameDownloadedImage = downloader.image(from: imageURL) // Uncomment to see the bug
var images = [UIImage?]()
images += [try? await downloadedImage]
//images += [try? await sameDownloadedImage]
print("Finished everything")
}
}
If you uncomment the code marked as Uncomment to see the bug, you will see that the code will go through many different await calls, but it will hang on the ine in the URLSession.shared.data(for: imageRequest) call. The app just hangs there and doesn't continue executing. Commenting the same line will let it work fine.
Are there any known workarounds for this? I would love to get this to work.
I have opened a feedback on this, linking it just in case