How to create dispatch queue in Swift 3

Creating a concurrent queue

let concurrentQueue = DispatchQueue(label: "queuename", attributes: .concurrent)concurrentQueue.sync {}  

Create a serial queue

let serialQueue = DispatchQueue(label: "queuename")serialQueue.sync { }

Get main queue asynchronously

DispatchQueue.main.async {}

Get main queue synchronously

DispatchQueue.main.sync {}

To get one of the background thread

DispatchQueue.global(qos: .background).async {}

Xcode 8.2 beta 2:

To get one of the background thread

DispatchQueue.global(qos: .default).async {}DispatchQueue.global().async {    // qos' default value is ´DispatchQoS.QoSClass.default`}

If you want to learn about using these queues .See this answer

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            }        }    }}

Compiled in XCode 8, Swift 3https://github.com/rpthomas/Jedisware

 @IBAction func tap(_ sender: AnyObject) {    let thisEmail = "emailaddress.com"    let thisPassword = "myPassword"     DispatchQueue.global(qos: .background).async {        // Validate user input        let result = self.validate(thisEmail, password: thisPassword)        // Go back to the main thread to update the UI        DispatchQueue.main.async {            if !result            {                self.displayFailureAlert()            }        }    }}