GCD创建单例常用的两种方法

//GCD单例
+(instancetype)share
{
    //整个生命周期只创建一次
    static GCDSingleton *object = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken,^{
        object = [[GCDSingleton alloc] init];
    });
    return object;
}
//synchonized单例
+(instancetype)defaultManager
{
    static GCDSingleton *object = nil;
    
    @synchronized(self) {
        if (object == nil) {
            object = [[GCDSingleton alloc] init];
        }

    }
        return object;
}
@end