title 2

this is some text in original format.

  • (id)sharedInstance {
    static SomeClass *sharedInstance = nil;
    static dispatch_once_t onceTocken; //必须保证有一个标记单次执行的token
    dispatch_once(&onceTocken, //需要传入tocken的指针
    ^{
    sharedInstance = [[self alloc] init];
    });
    return sharedInstance;
    }