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 CONCURRENT    But this doesn t compile in Swift 3     What is the preferred way to write this in Swift 3

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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     - gt  Void in      guard let strongSelf   self else   return        strongSelf flickrPhoto loadLargeImage   loadedFlickrPhoto  error in          if error    nil               print  error   error              else               DispatchQueue main async      - gt  Void in                 activityIndicator removeFromSuperview                   strongSelf imageView image   strongSelf flickrPhoto largeImage

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Update for swift 5  Serial Queue  let serialQueue   DispatchQueue init label   quot serialQueue quot   serialQueue async          code to execute     Concurrent Queue  let concurrentQueue   DispatchQueue init label   quot concurrentQueue quot   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

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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

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For Swift 3      DispatchQueue main async              Write your code here

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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

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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

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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

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let newQueue   DispatchQueue label   newname    newQueue sync         your code

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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

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DispatchQueue main async execute          code

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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

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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

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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

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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

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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

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