swift刷新主线程DispatchQueue.main.asy

 workingQueue.async {
// 在 workingQueue 中异步进行
print("努力工作")
Thread.sleep(forTimeInterval: 2)  // 模拟两秒的执行时间

DispatchQueue.main.async {
   // 返回到主线程更新 UI
   print("结束工作，更新 UI")
   }
 }

typealias Task = (_ cancel : Bool) -> Void

 func delay(_ time: TimeInterval, task: @escaping ()->()) ->  Task? {

func dispatch_later(_ block: @escaping ()->()) {
   let t = DispatchTime.now() + time
   DispatchQueue.main.asyncAfter(deadline: t, execute: block)
}

var closure: (()->Void)? = task
var result: Task?

let delayedClosure: Task = {
   cancel in
   if let internalClosure = closure {
       if (cancel == false) {
           DispatchQueue.main.async(execute: internalClosure)
       }
   }
   closure = nil
   result = nil
}

result = delayedClosure

dispatch_later {
   if let delayedClosure = result {
       delayedClosure(false)
   }
}

return result;

 }

  func cancel(_ task: Task?) {
task?(true)
 }
 delay(2) { print("2 秒后输出") }
 
 let task = delay(5) { print("拨打 110") }

 // 仔细想一想..
 // 还是取消为妙..
 cancel(task)


// 创建目标队列
 let workingQueue = DispatchQueue(label: "my_queue")


// 派发到刚创建的队列中，GCD 会负责进行线程调度

 workingQueue.async {
// 在 workingQueue 中异步进行
print("努力工作")
Thread.sleep(forTimeInterval: 2)  // 模拟两秒的执行时间

DispatchQueue.main.async {
   // 返回到主线程更新 UI
   print("结束工作，更新 UI")
   }
 }