dataTask() in a loop

Using Swift
2

It's much easier if you use Swift Concurrency to achieve what you want:

/// This function runs on the main thread
@MainActor func downloadAndShowError() async {
    do {
        // Try to download files from the urls
        // The function is suspended here, but the main thread is Not blocked.
        try await download(urls: [])
    } catch {
        // Show error if occurred, this will run on the main thread
        print("error occurred: \(error.localizedDescription)")
    }
}

/// This function asynchronously downloads data for all passed URLs.
func download(urls: [URL]) async throws {
    let session = URLSession(configuration: .default)
    for url in urls {
        // If an error occurs, then it will throw, loop will break and function throws, 
        // caller must deal with the error.
        let (data, response) = try await session.data(from: url)
        // Do something with data, response
        // You can even throw from here if you don't like the response...
    }
}
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