CF RunLoop VS GCD

Access the Main Thread like a Boss! 😎

The demo app you can play with and see the difference between using GCD dispatch_async approach versus CF RunLoop block execution on the Main Thread.

Two very different APIs, but the trick is that the Core Foundation approach with CFRunLoopPerformBlock allows us to choose a specific RunLoop mode we want to use for our block. Especially in the case of scrolling TableView, it makes a big difference since all scrolling happens with UITrackingRunLoopMode.

            switch self.cellImageAssignMode {
                
            case .GCD:
                DispatchQueue.main.async(execute: { () -> Void in
                    
                    let image = UIImage(data: data!)
                    cell.thumbnailImage.image = image
                })
                
            case .RunLoop:
                CFRunLoopPerformBlock(CFRunLoopGetMain(), RunLoop.Mode.tracking as CFTypeRef) {
                    
                    let image = UIImage(data: data!)
                    cell.thumbnailImage.image = image
                }
            }

Quickly scroll down to 2-4XXX cells, stop the scroll at once - and see how "GCD" tab cells are loading with noticeable delay versus "RunLoop" tab cells are assigned faster with minimal visible UI lags.

TableViews are loading identical data from a network in both tabs.

However, the left tab manually uses UITrackingRunLoopMode to update image data with Core Foundation CFRunLoopPerformBlock.

The right tab uses GCD API to access the Main Thread, essentially delegating RunLoop mode selection to Grand Central Dispatch.

It's advisable to run the app on a real device!

Copyright © 2019 Nikolay Gutorov. All rights reserved.