GCD Timer事件的精度

@interface ViewController ()

@property (nonatomic, strong)   dispatch_source_t timer;
@property (atomic, assign)   NSInteger   count;
@property (nonatomic, strong)   NSDate *startDate;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    [self testTimer];
    [self dumpResult];
}

- (void)setupTimer
{
    _startDate = [NSDate date];
    
    _timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, dispatch_get_main_queue());
    
    dispatch_source_set_timer(_timer,
                              dispatch_time(DISPATCH_TIME_NOW, 1 * NSEC_PER_SEC),
                              10 * NSEC_PER_USEC,
                              0);
    
    dispatch_source_set_event_handler(_timer, ^{
        self->_count++;
    });
    dispatch_resume(_timer);
}

- (void)dumpResult
{
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        while (YES) {
            [NSThread sleepForTimeInterval:3];
            NSLog(@"%lf per second", self->_count * 1.0 / [[NSDate date] timeIntervalSinceDate:_startDate] );
            self->_count = 0;
            _startDate = [NSDate date];
        }
    });
}

- (void)testTimer
{
    [self setupTimer];
}


- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}


@end

2018-08-21 20:18:59.344851+0800 TestGCDTimer[17447:7933588] 664.509536 per second
2018-08-21 20:19:02.345519+0800 TestGCDTimer[17447:7933588] 998.187963 per second
2018-08-21 20:19:05.347805+0800 TestGCDTimer[17447:7933588] 999.964033 per second
2018-08-21 20:19:08.353024+0800 TestGCDTimer[17447:7933588] 999.657229 per second
2018-08-21 20:19:11.354784+0800 TestGCDTimer[17447:7933588] 999.810779 per second
2018-08-21 20:19:14.355783+0800 TestGCDTimer[17447:7933588] 999.763704 per second
2018-08-21 20:19:17.359697+0800 TestGCDTimer[17447:7933588] 1000.090226 per second
2018-08-21 20:19:20.364868+0800 TestGCDTimer[17447:7933588] 999.988378 per second
2018-08-21 20:19:23.370107+0800 TestGCDTimer[17447:7933588] 999.985720 per second
2018-08-21 20:19:26.374239+0800 TestGCDTimer[17447:7933588] 1000.022002 per second
2018-08-21 20:19:29.375823+0800 TestGCDTimer[17447:7933588] 999.875706 per second


2018-08-21 20:19:47.485125+0800 TestGCDTimer[17450:7934123] 6615.815753 per second
2018-08-21 20:19:50.486199+0800 TestGCDTimer[17450:7934123] 9991.399568 per second
2018-08-21 20:19:53.490001+0800 TestGCDTimer[17450:7934123] 9994.962862 per second
2018-08-21 20:19:56.490189+0800 TestGCDTimer[17450:7934123] 9996.189939 per second
2018-08-21 20:19:59.490784+0800 TestGCDTimer[17450:7934123] 9994.127387 per second
2018-08-21 20:20:02.492282+0800 TestGCDTimer[17450:7934123] 9988.322134 per second
2018-08-21 20:20:05.495670+0800 TestGCDTimer[17450:7934123] 9997.735664 per second
2018-08-21 20:20:08.495762+0800 TestGCDTimer[17450:7934123] 9993.233265 per second
2018-08-21 20:20:11.496856+0800 TestGCDTimer[17450:7934123] 9994.565064 per second
2018-08-21 20:20:14.498354+0800 TestGCDTimer[17450:7934123] 9997.541106 per second


2018-08-21 20:20:56.694542+0800 TestGCDTimer[17454:7934900] 23341.699400 per second
2018-08-21 20:20:59.696130+0800 TestGCDTimer[17454:7934900] 33664.868549 per second
2018-08-21 20:21:02.697670+0800 TestGCDTimer[17454:7934900] 31380.877279 per second
2018-08-21 20:21:05.699141+0800 TestGCDTimer[17454:7934900] 34535.414907 per second
2018-08-21 20:21:08.700716+0800 TestGCDTimer[17454:7934900] 34488.215922 per second
2018-08-21 20:21:11.702206+0800 TestGCDTimer[17454:7934900] 34440.995680 per second
2018-08-21 20:21:14.703723+0800 TestGCDTimer[17454:7934900] 34449.645662 per second