How to create dispatch queue in Swift 3

Question

In Swift 2, I was able to create queue with the following code:

let concurrentQueue = dispatch_queue_create(\"com.swift3.imageQueue\", DISPATCH_QUEUE_CONCURR         


        

Answer 1

Compiles under >=Swift 3. This example contains most of the syntax that we need.

QoS - new quality of service syntax

weak self - to disrupt retain cycles

if self is not available, do nothing

async global utility queue - for network query, does not wait for the result, it is a concurrent queue, the block (usually) does not wait when started. Exception for a concurrent queue could be, when its task limit has been previously reached, then the queue temporarily turns into a serial queue and waits until some previous task in that queue completes.

async main queue - for touching the UI, the block does not wait for the result, but waits for its slot at the start. The main queue is a serial queue.

Of course, you need to add some error checking to this...

DispatchQueue.global(qos: .utility).async { [weak self] () -> Void in

    guard let strongSelf = self else { return }

    strongSelf.flickrPhoto.loadLargeImage { loadedFlickrPhoto, error in

        if error != nil {
            print("error:\(error)")
        } else {
            DispatchQueue.main.async { () -> Void in
                activityIndicator.removeFromSuperview()
                strongSelf.imageView.image = strongSelf.flickrPhoto.largeImage
            }
        }
    }
}