How to create dispatch queue in Swift 3 - ios

Question

In Swift 2, I was able to create queue with the following code:
let concurrentQueue = dispatch_queue_create("com.swift3.imageQueue", DISPATCH_QUEUE_CONCURRENT)
But this doesn't compile in Swift 3.
What is the preferred way to write this in Swift 3?

Answer 1

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

Answer 2

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
}
}
}
}

Answer 3

Compiled in XCode 8, Swift 3
https://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()
}
}
}
}

Answer 4

Since the OP question has already been answered above I just want to add some speed considerations:
It makes a lot of difference what priority class you assign to your async function in DispatchQueue.global.
I don't recommend running tasks with the .background thread priority especially on the iPhone X where the task seems to be allocated on the low power cores.
Here is some real data from a computationally intensive function that reads from an XML file (with buffering) and performs data interpolation:
Device name / .background / .utility / .default / .userInitiated / .userInteractive
iPhone X: 18.7s / 6.3s / 1.8s / 1.8s / 1.8s
iPhone 7: 4.6s / 3.1s / 3.0s / 2.8s / 2.6s
iPhone 5s: 7.3s / 6.1s / 4.0s / 4.0s / 3.8s
Note that the data set is not the same for all devices. It's the biggest on the iPhone X and the smallest on the iPhone 5s.

Answer 5

Update for swift 5
Serial Queue
let serialQueue = DispatchQueue.init(label: "serialQueue")
serialQueue.async {
// code to execute
}
Concurrent Queue
let concurrentQueue = DispatchQueue.init(label: "concurrentQueue", qos: .background, attributes: .concurrent, autoreleaseFrequency: .inherit, target: nil)
concurrentQueue.async {
// code to execute
}
From Apple documentation:
Parameters
label
A string label to attach to the queue to uniquely identify it in debugging tools such as Instruments, sample, stackshots, and crash reports. Because applications, libraries, and frameworks can all create their own dispatch queues, a reverse-DNS naming style (com.example.myqueue) is recommended. This parameter is optional and can be NULL.
qos
The quality-of-service level to associate with the queue. This value determines the priority at which the system schedules tasks for execution. For a list of possible values, see DispatchQoS.QoSClass.
attributes
The attributes to associate with the queue. Include the concurrent attribute to create a dispatch queue that executes tasks concurrently. If you omit that attribute, the dispatch queue executes tasks serially.
autoreleaseFrequency
The frequency with which to autorelease objects created by the blocks that the queue schedules. For a list of possible values, see DispatchQueue.AutoreleaseFrequency.
target
The target queue on which to execute blocks. Specify DISPATCH_TARGET_QUEUE_DEFAULT if you want the system to provide a queue that is appropriate for the current object.

Answer 6

I did this and this is especially important if you want to refresh your UI to show new data without user noticing like in UITableView or UIPickerView.
DispatchQueue.main.async
{
/*Write your thread code here*/
}

Answer 7

DispatchQueue.main.async {
self.collectionView?.reloadData() // Depends if you were populating a collection view or table view
}
OperationQueue.main.addOperation {
self.lblGenre.text = self.movGenre
}
//use Operation Queue if you need to populate the objects(labels, imageview, textview) on your viewcontroller

Answer 8

let concurrentQueue = dispatch_queue_create("com.swift3.imageQueue", DISPATCH_QUEUE_CONCURRENT) //Swift 2 version
let concurrentQueue = DispatchQueue(label:"com.swift3.imageQueue", attributes: .concurrent) //Swift 3 version
I re-worked your code in Xcode 8, Swift 3 and the changes are marked in contrast to your Swift 2 version.

Answer 9

Swift 3
you want call some closure in swift code then you want to change in storyboard ya any type off change belong to view your application will crash
but you want to use dispatch method your application will not crash
async method
DispatchQueue.main.async
{
//Write code here
}
sync method
DispatchQueue.main.sync
{
//Write code here
}

Answer 10

DispatchQueue.main.async(execute: {
// write code
})
Serial Queue :
let serial = DispatchQueue(label: "Queuename")
serial.sync {
//Code Here
}
Concurrent queue :
let concurrent = DispatchQueue(label: "Queuename", attributes: .concurrent)
concurrent.sync {
//Code Here
}

Answer 11

For Swift 3
DispatchQueue.main.async {
// Write your code here
}

Answer 12

let newQueue = DispatchQueue(label: "newname")
newQueue.sync {
// your code
}

Answer 13

it is now simply:
let serialQueue = DispatchQueue(label: "my serial queue")
the default is serial, to get concurrent, you use the optional attributes argument .concurrent

Answer 14

DispatchQueue.main.async(execute: {
// code
})

Answer 15

You can create dispatch queue using this code in swift 3.0
DispatchQueue.main.async
{
/*Write your code here*/
}
/* or */
let delayTime = DispatchTime.now() + Double(Int64(0.5 * Double(NSEC_PER_SEC))) / Double(NSEC_PER_SEC)
DispatchQueue.main.asyncAfter(deadline: delayTime)
{
/*Write your code here*/
}