This repo is the steps breaking down from this excellent tutorial and an update for swift3 + xcode8. I seperated each step into its own commit, you can check the commit history for details.

The major difference is on GCD part, for NSOperation part, the changes are minor.

Example from here

qos - new quality of service syntax

weak self - to disrupt retain cycles

async global background queue - for network query

async main queue - for touching the UI.

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

DispatchQueue.global(qos: .background).async { [weak self]
  () -> Void in
  self?.flickrPhoto.loadLargeImage {
      loadedFlickrPhoto, error in
      if error != nil {
          print("error:\(error)")
      } else {
      
          DispatchQueue.main.async {
              () -> Void in
              activityIndicator.removeFromSuperview()
              self?.imageView.image = self?.flickrPhoto.largeImage
          }
      }
  }
}

swift2 version:

dispatch_get_main_queue()

swift3 version:

DispatchQueue.main    

swift2 version:

let queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)

swift3 version:

let queue = DispatchQueue.global(qos: .default) 

swift2 version:

let queue = dispatch_queue_create("com.cyper.xxx", DISPATCH_QUEUE_SERIAL)

swift3 version:

let queue = DispatchQueue(label: "com.cyper.xxx")

DispatchQueue by default is serial queue, you don't have to specify it in the initializer.

swift2 version:

let queue = dispatch_queue_create("com.cyper.xxx", DISPATCH_QUEUE_CONCURRENT)

swift3 version:

let queue = DispatchQueue(label: "com.cyper.xxx", qos: .userInitiated, attributes: .concurrent)

1. Removed the NS prefix
2. Simplified the method name
3. You can use xcode auto-fix

http://www.appcoda.com/ios-concurrency/

https://medium.com/swift-and-ios-writing/a-quick-look-at-gcd-and-swift-3-732bef6e1838#.ueryj2b2h

https://www.logcg.com/archives/2040.html

http://stackoverflow.com/questions/37805885/how-to-create-dispatch-queue-in-swift-3

https://github.com/uniquejava/iOSConcurrencyDemo/blob/master/iOSConcurrencyDemo/ViewController.swift