GCD를 이용한 thread-safe한 singleton 생성자

GCD를 이용한 thread-safe한 singleton 생성자 예제.

+ (instancetype)sharedManager
{
    static PhotoManager *sharedPhotoManager = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        sharedPhotoManager = [[PhotoManager alloc] init];
        sharedPhotoManager->_photosArray = [NSMutableArray array];
    });
    return sharedPhotoManager;
}

출처: http://www.raywenderlich.com/60749/grand-central-dispatch-in-depth-part-1