grand-central-dispatch

I have a UITableView that displays images associated with contacts in each row. In some cases these images are read on first display from the address book contact image, and where there isn't one they are an avatar rendered based on stored data. I presently have these images being updated on a background thread using GCD. However, this loads the images in the order they were requested, which means during rapid scrolling the queue becomes lengthy and when the user stops scrolling the current cells are the last to get updated. On the iPhone 4, the problem isn't really noticeable, but I am keen

I have a method that accepts a block and a completion block. The first block should run in the background, while the completion block should run in whatever queue the method was called. For the latter I always used dispatch_get_current_queue() , but it seems like it's deprecated in iOS 6 or higher. What should I use instead? Catfish_Man The pattern of "run on whatever queue the caller was on" is appealing, but ultimately not a great idea. That queue could be a low priority queue, the main queue, or some other queue with odd properties. My favorite approach to this is to say "the completion

I have a scenario in my app, where I want to do some time consuming task which consists of some data processing as well as UI update, in a method. My method looks like this, - (void)doCalculationsAndUpdateUIs { // DATA PROCESSING 1 // UI UPDATE 1 // DATA PROCESSING 2 // UI UPDATE 2 // DATA PROCESSING 3 // UI UPDATE 3 } As it is time consuming I wanted to do the data processing on the background thread, using, dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, NULL), ^{ But as both data processing and UI updates are in the same method, I wanted to move only the UI updates

In my app I have a function that makes an NSRURLSession and sends out an NSURLRequest using sesh.dataTaskWithRequest(req, completionHandler: {(data, response, error) In the completion block for this task, I need to do some computation that adds a UIImage to the calling viewcontroller. I have a func called func displayQRCode(receiveAddr, withAmountInBTC:amountBTC) that does the UIImage-adding computation. If I try to run the view-adding code inside of the completion block, Xcode throws an error saying that I can't use the layout engine while in a background process. So I found some code on SO

I'm just playing around with GCD and I've written a toy CoinFlipper app. Here's the method that flips the coins: - (void)flipCoins:(NSUInteger)nFlips{ // Create the queues for work dispatch_queue_t mainQueue = dispatch_get_main_queue(); dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, NULL); // Split the number of flips into whole chunks of kChunkSize and the remainder. NSUInteger numberOfWholeChunks = nFlips / kChunkSize; NSUInteger numberOfRemainingFlips = nFlips - numberOfWholeChunks * kChunkSize; if (numberOfWholeChunks > 0) { for (NSUInteger index = 0;

I ran into a scenario where I had a delegate callback which could occur on either the main thread or another thread, and I wouldn't know which until runtime (using StoreKit.framework ). I also had UI code that I needed to update in that callback which needed to happen before the function executed, so my initial thought was to have a function like this: -(void) someDelegateCallback:(id) sender { dispatch_sync(dispatch_get_main_queue(), ^{ // ui update code here }); // code here that depends upon the UI getting updated } That works great, when it is executed on the background thread. However,