1 .h文件:

sharedMyOperationBySynchronized是互斥锁方式创建单例的类方法

sharedMyOperationByDispatchOnce是GCD一次性执行方式创建单例的类方法:

@interface MyOperation : NSOperation
+ (instancetype)sharedMyOperationBySynchronized;
+ (instancetype)sharedMyOperationByDispatchOnce;
@end

2 .m文件:

@implementation MyOperation
+ (instancetype)sharedMyOperationBySynchronized{
    
    static id _instanceType = nil;
    @synchronized (_instanceType) {
        
        _instanceType = [[MyOperation alloc]init];
        
    }
    return _instanceType;
}
+ (instancetype)sharedMyOperationByDispatchOnce{
    
    static id _instanceType = nil;
    
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        
        _instanceType = [[MyOperation alloc]init];
    });
    
    return _instanceType;
}
@end

3 演示代码:

#import "ViewController.h"
#import "MyOperation.h"
#define ENOUGH_LARGE_NUMBER 10000
@interface ViewController ()
@end
@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
}
- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

/*
      将两种获取单例对象分别放在For循环中,获取For循环前的精确时间,再获取For循环执行完毕后的精确时间,对比两种方式的效率
*/
- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{
    
    CFAbsoluteTime startTimeSync = CFAbsoluteTimeGetCurrent();
    for (int i = 0; i < ENOUGH_LARGE_NUMBER; i ++) {
        
        MyOperation *operationBySynchronized = [MyOperation sharedMyOperationBySynchronized];
        
    }
    CFAbsoluteTime endTimeSync = CFAbsoluteTimeGetCurrent();
    CFAbsoluteTime startTimeGCD = CFAbsoluteTimeGetCurrent();
    for (int i = 0; i < ENOUGH_LARGE_NUMBER; i ++) {
        
        MyOperation *operationByDispatchOnce = [MyOperation sharedMyOperationByDispatchOnce];
        
    }
    CFAbsoluteTime endTimeGCD = CFAbsoluteTimeGetCurrent();
    
    NSLog(@"sharedMyOperationBySynchronized:%f",endTimeSync - startTimeSync);
    NSLog(@"sharedMyOperationByDispatchOnce:%f",endTimeGCD - startTimeGCD);

}
@end

4 输出结果:

2016-06-09 20:23:22.712 07-单例效率比较[2166:395895] sharedMyOperationBySynchronized:0.012765
2016-06-09 20:23:22.712 07-单例效率比较[2166:395895] sharedMyOperationByDispatchOnce:0.000792

For循环的次数越大,体现越明显

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