GCD创建单例常用的两种方法

 1 //GCD单例
 2 +(instancetype)share
 3 {
 4     //整个生命周期只创建一次
 5     static GCDSingleton *object = nil;
 6     static dispatch_once_t onceToken;
 7     dispatch_once(&onceToken,^{
 8         object = [[GCDSingleton alloc] init];
 9     });
10     return object;
11 }
12 //synchonized单例
13 +(instancetype)defaultManager
14 {
15     static GCDSingleton *object = nil;
16     
17     @synchronized(self) {
18         if (object == nil) {
19             object = [[GCDSingleton alloc] init];
20         }
21 
22     }
23         return object;
24 }
25 @end