singleton difference

+ (BMHttpAudioStreamManager*) getInstance {
    if (singletonInstance == nil) {
        singletonInstance = [[super alloc] init];
    }
    return singletonInstance;
}


+ (instancetype)sharedGameData {
    static id sharedInstance = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        sharedInstance = [[self alloc] init];
    });
    return sharedInstance;
}