Question

I have a C function(a callback function in Audio Queue Services) and I want to send message to self. How to do that?
If I type in [self message], there is an error:

Use of undeclared identifier 'self'

Answer 1

You don’t perform objc messages in realtime callbacks, such as audio. The reason for this is that objc messaging is not constant time, and may lock, resulting in missed deadlines, resulting in audio dropouts. Static or dynamic (virtual) C++ calls and C function calls are of course constant time, and suitable for realtime contexts.

If it were not an realtime/audio callback, then one option would be to pass self as the user info or context parameter:

void SomeCallback(t_stuff* const stuff, void* userInfo) {
  MONClass * Self = (MONClass*)userInfo;
  [Self doSomething];
}