代码耗时统计：单例实现的dispatch_once与@synchronized方式对比

#import "ViewController.h"
#import

static dispatch_once_t once;

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.

//获取@synchronized执行时间
     CGFloat  t_s = BNRTimeBlock(^{
        @synchronized(self) {
            [NSThread sleepForTimeInterval:1];
        }
     });
    

//获取dispatch_once执行时间
    CGFloat t_d = BNRTimeBlock(^{
        dispatch_once(&once, ^{
            [NSThread sleepForTimeInterval:1];
        });
    });

}

//获取block执行时间

CGFloat BNRTimeBlock (void (^block)(void)) {
    mach_timebase_info_data_t info;
    if (mach_timebase_info(&info) != KERN_SUCCESS) return -1.0;
    
    uint64_t start = mach_absolute_time ();
    block ();
    uint64_t end = mach_absolute_time ();
    uint64_t elapsed = end - start;
    
    uint64_t nanos = elapsed * info.numer / info.denom;
    return (CGFloat)nanos / NSEC_PER_SEC;
}

@end