dispatch_once weird behavior

Are you sure that the debugger isn’t lying to do? To check this, add an NSLog to -[OGAKeyManager init] and see starting your app logs twice.

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Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

Unfortunately @eskimo it is not. I printed the memory addresses of the static instance iVar, and I get 2 different addresses, one for each time I enter the dispatch_once (called from framework #1 then #2). After that, I never enter the dispatch_once again :-/

FYI, here are the imported framework. You can see that they are imported as local frameworks inside the workspace

@eskimo I just made a small sample project (1 objC framework with dispatch_once, 1 swift framework calling the #1 and an app including both and calling both) : it behaves as expected (dispatch_once is only called once). So it musts come from our project. We use, through a bridging header, some internal objC classes (non public) to do some work. Do you think that using some non public objects can lead to such a behavior (since Xcode would not find the Classes inside the framework, it loads a copy of the development local files, hence loading 2 copies of the framework in memory ? Thanks

I just made a small sample project … it behaves as expected

Right. That was gonna be my next question (-:

Given that, the most likely cause of this problem in your main app is that you have two different onceToken variables, protecting two difference singletons. It’s hard to say for sure how that came about, and it certainly is weird because the Objective-C runtime normally kvetches if you try to register two different copies of a class with the same name.

What I’d do next is tweak your code to look something like this:

+ (instancetype)shared {
    static dispatch_once_t onceToken;
    static OGAKeyManager *instance = nil;
 
    dispatch_once(&onceToken, ^{
        NSLog(@"%p", &onceToken);
        instance = [[self alloc] init];
    });
 
    return instance;
}

Then set a breakpoint on the log line, step over it, and see what gets logged. I have to presume it’s two different addresses. You can then look up what Mach-O images contain those addresses.

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Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

Ok, so as expected @eskimo, I have 2 dispatch_once_t, though I cannot figure out why. The first memory graph (the one from inside the app itself) seems very small IMO, at least compared to the other which have a lot of objects in memory. Maybe it's a lead ?

First call (shared inside the app):

Second call (shared inside the framework2):

What do you mean by “You can then look up what Mach-O images contain those addresses.”?

Consider this:

@implementation SomeSingleton
 
+ (SomeSingleton *)shared {
    static dispatch_once_t sOnceToken;
    static SomeSingleton * sShared;
    dispatch_once(&sOnceToken, ^{
        NSLog(@"%p", &sOnceToken);
        sShared = [[SomeSingleton alloc] init];
    });
    return sShared;
}
 
…
 
@end

If I set a breakpoint on the line after the NSLog, I see this printed:

2023-09-08 09:15:44.923100+0100 Test736851[4985:12779017] sOnceToken: 0x109f8dda8

Then I do this:

(lldb) p/a 0x100a13da8
(long) $0 = 0x0000000100a13da8 Test736851`shared.sOnceToken

See the Test736851 before the backquote (`)? That tells me the name of the Mach-O image containing the shared.sOnceToken static variable. In this case it the name of my test app, but I suspect that in your case you’ll see different values for the each ‘singleton’ that gets created.

If you see different addresses but the same Mach-O image value, you can use a link map to investigate. See Using a Link Map to Track Down a Symbol’s Origin.

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Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"