Question

I’m running into a weird issue with XCode 4.5, the one supporting the new iOS6.

In most of my apps, I make a State class as a singleton accessible from everywhere for convenience, but with latest XCode, it seems like after I set any non-static pointer member to some object, right after the assignment the value is back to NULL.

Even weirder is I only see the issue if I start a new project from scratch, not if I load an older project created with an earlier version of XCode. I looked at compiler settings, and everything looks the same. The issue only appears if I test on the actual device (iPhone4 running iOS6). The simulator does not show this problem.

Here’s the relevent code :

State.h

class State
{
public:

    State();
    ~State();

     static State& Get();

private:
    static State * s_state;

State.mm

State* State::s_state = nil;

State& State::Get()
{
    if(s_state==nil)
        s_state = new State();
    return *(s_state);
}

Example usage assuming State has a non-static member Object * m_object :

void SomeClass::DoSomething()
{
    State::Get().SetObject( new Object() );

    // this will return null with newly created XCode 4.5 projects
    State::Get().GetObject();

** EDIT **
Regarding thread safety-ness, I’d like to know if the 2 cases below are considered “multi-threaded” scenarios.

I have one timer using display link for my opengl loop

[displayLink addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];

And I have one timer responsible for updating the game logic that I init this way

timer = [NSTimer scheduledTimerWithTimeInterval:1.f/60.f target:self selector:@selector(timerUpdate) userInfo:nil repeats:YES];
[[NSRunLoop mainRunLoop] addTimer:m_timer forMode:NSRunLoopCommonModes];

So if I call State::Get() from both these loops, is this considered a threaded scenario?

Thank you for your help.
– Marc

Answer 1

Ok I found out what my issue was and thought I’d share with you all. Although it doesn’t have anything to do with single/static classes, this kind of issue can be hard to debug.

In my State class, I had a member available only to a specific config :

#ifdef SOME_CONFIG
    int m_someValue;
#endif

The problem in this case was that at compile time, SOME_CONFIG was actually defined, but undefined elsewhere according to target conditionals etc, causing the variable to exist on the stack but never inited/used etc. Just having the variable in the header was causing the issue (even if I didn’t make any call using it.)

Hope this can help someone out there.

Thanks.