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Using Dispatch Queues for Concurrency

Grand Central Dispatch (GCD) provides a powerful way to handle concurrency in your Swift applications, ensuring that long-running tasks don't block the main thread and thus keep the user interface responsive.

Key Concepts​

  • Serial Queues: Execute tasks one at a time in a FIFO order.
  • Concurrent Queues: Execute multiple tasks simultaneously as resources allow.

Implementation Example​

Here's how to use GCD to handle photo processing on a background thread while keeping the UI responsive:

let processingQueue = DispatchQueue(label: "Photo processing queue")

func generatePhotoBook(with photos: [UIImage]) {
    processingQueue.async { [weak self] in
        let resizer = PhotoResizer()
        let builder = PhotoBookBuilder()

        // Perform intensive tasks
        let photosForBook = resizer.scaleToSmallest(of: photos)
        let photobookURL = builder.buildPhotobook(with: photosForBook)

        // Update the UI on the main queue
        DispatchQueue.main.async {
            let previewController = UIDocumentInteractionController(url: photobookURL)
            previewController.delegate = self
            previewController.presentPreview(animated: true)
        }
    }
}

How It Works​

GCD allows you to offload heavy tasks to background threads, freeing the main thread for UI updates. This results in a smoother user experience even during intensive operations.

Learn More about Dispatch Queues→