The Most Common GCD (Greate Central Dispatch)

gcd_demo.swift

override func viewDidLoad() {
      let workingQueue = dispatch_queue_create("myqueue", nil)
        
        dispatch_async(workingQueue) {
            print("working hard...")
            NSThread.sleepForTimeInterval(2)
            
            dispatch_async(dispatch_get_main_queue()){
                print("Work Done, updateUI")
            }
        }
  
}