IOS GCD执行并发编程

 1 var label = UILabel()
 2 override func viewDidLoad() {
 3 super.viewDidLoad()
 4 // Do any additional setup after loading the view,
 typically from a nib.
 5
 6 label.frame = CGRect(x：0, y：0, width：320, height：
 
7 label.text = “Loading……”
 8 label.font = UIFont(name：“Arial”, size：24)
 9 label.backgroundColor = UIColor.orange
 10 label.numberOfLines = 0
 11 label.lineBreakMode =
 NSLineBreakMode.byWordWrapping
 12 self.view.addSubview(label)
 13
 14 let apiURL =
 URL(string：“http：//ip.taobao.com/service/getIpInfo.php？
 ip=27.156.152.57”)
 15
 16 let globalQueue = DispatchQueue.global()
 17 globalQueue.async{
 18 let result = try？Data(contentsOf：apiURL！)
 19 let message = String(data：result！, encoding：
 String.Encoding.utf8)
 20 DispatchQueue.main.async
 21 {
 22 self.label.text = message
 23 }
 24 }
 25 }
//
 1 override func viewDidLoad() {
 2 super.viewDidLoad()
 3 // Do any additional setup after loading the view,
 typically from a nib.
 4 print(“开始任务，并显示Loading动画。”)
 5
 6 let group = DispatchGroup()
 7 let globalQueue = DispatchQueue.global()
 8
 9 globalQueue.async(group：group, execute： {_ in
 10 print(“从远程服务器加载用户头像。”)
 11 })
 12
 13 globalQueue.async(group：group, execute： {_ in
 14 print(“根据用户id获得年度所有的交易额纪录。”)
 15 })
 16
 17 globalQueue.async(group：group, execute： {_ in
 18 print(“根据用户id获得所有被用户收藏的商品名称。”)
 19 })
 20
 21 group.notify(queue：globalQueue, execute：{_ in
 22 print(“完成所有任务，隐藏Loading动画。”)
 23 })
 24 }