API requires coupling of different modules

[mikebenfield]

Suppose my program has one video module and one audio module. They each use SDL. I don't want the two modules to know about each other, or whether any other part of the program is also using SDL. Maybe the two modules even come from different crates.

With the SDL C API, this is fine. There's a function SDL_WasInit, so each component of my program can check that and initialize if necessary.

With rust-sdl2, as far as I can tell there's no way to hide away SDL in multiple modules like this. Each module has to get access to the Sdl struct, and the only wait to do that is to call init. Once one module has called init, the other module will receive an error from init and can't proceed.

[sagebind]

This should be easily fixable, just allow creating multiple Sdl instances. SDL2 already refcounts its lifecycle, so this should be fine if it is coded correctly.

Actually, I wonder if we could have an alternate design for subsystems. Something like this:

fn do_video_stuff() {
    // Call SDL_InitSubSystem(SDL_INIT_VIDEO)...
    let video = sdl2::VideoSubsystem::init();

    loop {
        // ...
    }

    // Call SDL_QuitSubSystem(SDL_INIT_VIDEO) on drop...
}

This code is re-entrant, since SDL already refcounts calls to SDL_InitSubSystem() and SDL_QuitSubSystem() for us. The only problem is when to call SDL_Quit().SDL_Init() is useless, it is not required to be called. I bet we could refcount the need to call that too.

I think the current design is to be pretty strict about keeping subsystems on the main thread that are not thread safe.

[aperrot42]

Maybe related to that, but I have a hard time finding VideoSubsystem type definition (and so does my IDE).