Swift中GCD的使用

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)) {
　　doSomething() // 耗时操作
　　dispatch_async(dispatch_get_main_queue()) {
　　　　updateUI() // 更新主线程
　　}
}

let queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)
let group = dispatch_group_create()
for (id obj in array) {
    dispatch_group_async(group, queue) {
        self.doWork(obj)
    }
}
dispatch_group_notify(group, queue) {
    self.doneWork
}
// 如果是在OS X 10.8或iOS 6以及之后版本中使用，Dispatch Queue将会由ARC自动管理，如果是在此之前的版本，需要自己手动释放
// dispatch_release(group)

func delay(delay: Double, closure: () -> ()) {
    let delayTime = dispatch_time(DISPATCH_TIME_NOW, Int64(delayInSeconds * Double(NSEC_PER_SEC)))
    dispatch_after(delayTime, dispatch_get_main_queue(), closure)
}
delay(0.4) {
    // do stuff
}