typedef CF_OPTIONS(CFOptionFlags, CFRunLoopActivity) {
    kCFRunLoopEntry = (1UL << 0),   //即将进入Runloop
    kCFRunLoopBeforeTimers = (1UL << 1),    //即将处理NSTimer
    kCFRunLoopBeforeSources = (1UL << 2),   //即将处理Sources
    kCFRunLoopBeforeWaiting = (1UL << 5),   //即将进入休眠
    kCFRunLoopAfterWaiting = (1UL << 6),    //刚从休眠中唤醒
    kCFRunLoopExit = (1UL << 7),            //即将退出runloop
    kCFRunLoopAllActivities = 0x0FFFFFFFU   //所有状态改变
};