CFRunLoopObserver監(jiān)聽者，runloop事件。

public struct CFRunLoopActivity : OptionSet, @unchecked Sendable {

    public init(rawValue: CFOptionFlags)

    public static var entry: CFRunLoopActivity { get }

    public static var beforeTimers: CFRunLoopActivity { get }

    public static var beforeSources: CFRunLoopActivity { get }

    public static var beforeWaiting: CFRunLoopActivity { get }

    public static var afterWaiting: CFRunLoopActivity { get }

    public static var exit: CFRunLoopActivity { get }

    public static var allActivities: CFRunLoopActivity { get }
}

entry：即將進(jìn)入運(yùn)行循環(huán)
beforeTimers:即將處理timers
beforeSources：即將處理sources
beforeWaiting：即將等待，即將進(jìn)入休眠
afterWaiting：休眠之后，剛從休眠喚醒
exit：退出runloop循環(huán)

觀察runloop的狀態(tài)變化

public func CFRunLoopObserverCreateWithHandler(
_ allocator: CFAllocator!,//分配的空間
_ activities: CFOptionFlags, //要監(jiān)聽的狀態(tài)
_ repeats: Bool, 
_ order: CFIndex, 
_ block: ((CFRunLoopObserver?, CFRunLoopActivity) -> Void)!) 
-> CFRunLoopObserver!

let actitities = CFRunLoopActivity.allActivities //actitities 傳入要監(jiān)聽的所有狀態(tài)
        let allocator =  CFAllocatorGetDefault().takeUnretainedValue()
        let observer =  CFRunLoopObserverCreateWithHandler(allocator, 
                                                           actitities.rawValue,
                                                           true,
                                                           0) { observer, activity in
            switch activity {
            case .entry :
                print("進(jìn)入runloop循環(huán)")
            case .beforeTimers:
                print("即將處理timers")
            case .beforeSources:
                print("即將處理Source")
            case .beforeWaiting:
                print("即將休眠")
            case .afterWaiting:
                print("剛從休眠喚醒")
            case .exit:
                print("runloop循環(huán)結(jié)束")
            default:
                break
            }
        }
        CFRunLoopAddObserver(runloop, observer, .defaultMode)