gistfile1.m

/// .h
@interface mySingleton : NSObject
@property (nonatomic, strong) id someData;
+ (id)sharedInstance;
+ (void)probablySuperfluousStartup;
+ (void)probablyUnnecessaryShutdown;
@end 

/// .m
static mySingleton *sharedInstance;

@implemenation mySingleton

+ (void)startup
{
    [self sharedInstance];
}

+ (void)shutdown
{
    self.someData = nil;
}

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

- (instanceType)init
{
    self = [super init];
    if (self)
    {
        _someData = [NSObject new];
    }
    return self;
}

@end