safe __attribute__((constructor)) function classes

Question

Is it safe to use classes defined in you own project within __attribute__((constructor)) functions? Has the objective-C runtime had a chance to do what it needs to do with your classes when __attribute__((constructor)) functions are called? Or am I misunderstanding how the runtime loads classes and there is no difference between library class and your own in this context?

Answer 1

I'll suggest you use + initialize or + load rather than the attribute, but that is my preference.

The + load method of a class is called when the class is loaded by the runtime.

The + initialize method of a class is called before any other method in the class.

From the docs for load:

On Mac OS X v10.5, the order of initialization is as follows:

1. All initializers in any framework you link to.
2. All +load methods in your image.
3. All C++ static initializers and C/C++ attribute(constructor) functions in your image.
4. All initializers in frameworks that link to you.

In addition:

• A class’s +load method is called after all of its superclasses' +load methods.
• A category +load method is called after the class's own +load method.

In a +load method, you can therefore safely message other unrelated classes from the same image, but any +load methods on those classes may not have run yet.

Which makes it clear any attributed or + load methods will run after the runtime is initialized. And as + load is a method on your class and is run before any attributed methods then before either the runtime must have set up your class.