比Timer更加精准的计时器 GCD

- (void)viewDidLoad {
    [super viewDidLoad];
    NSLog(@"begin");
   //队列
   // dispatch_queue_t queue = dispatch_queue_create(0, 0);//子线程
    dispatch_queue_t queue = dispatch_get_main_queue();//主线程
    //创建定时器
    dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
    //设置时间
    uint64_t star = 2.0;//2秒后开始执行
    uint64_t intervale = 1.0;//每隔1秒执行
    
    dispatch_source_set_timer(timer,dispatch_time(DISPATCH_TIME_NOW, star * NSEC_PER_SEC) ,intervale * NSEC_PER_SEC ,0);
    //    //设置回调。方法一
    //    dispatch_source_set_event_handler(timer, ^{
    //        NSLog(@"1111======%@",[NSThread currentThre
    dispatch_source_set_event_handler_f(timer, timerFire);
    
    dispatch_resume(timer);
    
    self.timer = timer;
}
//
void  timerFire(void *parma){
     NSLog(@"1111======%@",[NSThread currentThread]);//打印看看在什么线程上执行
    
}