How to use barrier

Example:
https://github.com/lingzt/BarrierPra
By using the barrier, I can make sure every time getter starting after the previous setter finished.

#import "ViewController.h"

NSString *_name;
@interface ViewController ()
@property (nonatomic, strong, readwrite) NSString *name;@property (nonnull, strong, nonatomic) dispatch_queue_t syncQueue;@end
@implementation ViewController- (void)viewDidLoad {

    [super viewDidLoad];    //并行队列   set up on global queue    _syncQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);    for(int i=0; i<1000; i++){
        NSString *tempName = [NSString stringWithFormat:@"%d",i];        [self name];        [self setName:tempName];
    }

}


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




//用同步  sync with global queue- (NSString *)name{
    __block NSString *localName;    dispatch_sync(_syncQueue, ^{
        localName =_name;        NSLog(@"getter");        NSLog(localName);    });    return localName;}
//利用异步栅栏块  async with global que, with barrier- (void)setName:(NSString *)name{
    dispatch_barrier_async(_syncQueue, ^{
        _name = name;        NSLog(@"settter");        NSLog(_name);    });}


@end