创建单利的类:

#import "YQConfig.h"

@implementation YQConfig

+(instancetype)config{
    static YQConfig*instance;
    static dispatch_once_t onceToken;
    
    dispatch_once(&onceToken, ^{
        instance=[[YQConfig alloc]init];
    });
    
    return instance;
}


+(instancetype)configSync{
    
    static YQConfig*instance;
    @synchronized (self) {
        if (instance==nil) {
            instance=[[YQConfig alloc]init];
            
        }
    }
    
    
    return instance;
}

@end

ViewController.m中使用demo来测试两种方法性能的差别:

-(void)demo{

//disptach_once
double time1=CFAbsoluteTimeGetCurrent();

    for (int i=0; i<999*99; i++) {
        dispatch_async(dispatch_get_global_queue(0, 0), ^{
            
            YQConfig*config5=[YQConfig config];
           
        });
    }

double time2=CFAbsoluteTimeGetCurrent();

NSLog(@"dispatch: %f ",time2-time1 );






//同步锁
double time3=CFAbsoluteTimeGetCurrent();

for (int i=0; i<999*999; i++) {
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        
        YQConfig*config5=[YQConfig configSync];
        
    });
}

double time4=CFAbsoluteTimeGetCurrent();

NSLog(@"同步锁:%f ",time4-time3 );

}

运行结果:
2016-07-19 13:34:39.363 单例模式[1058:311069] dispatch: 0.186492 
2016-07-19 13:34:43.112 单例模式[1058:311069] 同步锁:3.745988 

从运行结果就可以看出,单利中使用dispatch 的方法时间比 同步锁@synchronized 性能多出数倍之多

开发中单利使用的平率很大

static dispatch_once_t onceToken;
dispatch_once(&onceToken,^{

});