Swift3.0-DisPatch

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        clorse { (json) in
            print(json)
        }
    }

    func clorse(completion:@escaping (_ json: [String])->()) {

        let workingQueue = DispatchQueue(label: "workingQueue")

        workingQueue.async {

            // 延迟操作
            print("努力工作")

            Thread.sleep(forTimeInterval: 2.0)

            let json = ["ac","mym"]

            DispatchQueue.main.async {

                print("结束工作")

                // 主线程更新 回调
                completion(json)
            }

        }

    }

}