[LUA] Can you unsubscribe from register_frame, register_start etc?

[Jakobud]

For older versions of MAME that still rely on register_frame, register_start, etc notifiers, is there some sort of "unsubscribe" functionality for them?

[cuavas]

register_start, register_frame, etc. are deprecated and will be removed at some point. You should use add_machine_reset_notifier, add_machine_frame_notifier, etc. (see the Emulator Interface documentation). These functions return notifier subscriptions which allow unsubscribing.

You can’t manage subscriptions created with the register_X functions. The closest you can do is to subscribe using an anonymous trampoline function that calls the real function by name, and then reassign the name with a function that does nothing (or does something else) when you no longer need it.

For example:

function on_frame()
    -- do something here
end

emu.register_frame(function () on_frame() end)

-- replace frame function with one that does nothing
on_frame = function () end

Note that all the callbacks will still be called, so it’s not a great idea to try and subscribe and unsubscribe numerous times like this.

[Jakobud]

Okay I tried the trampoline function approach and it seemed to work, however, it looks like emu.register_frame_done will continue running even when I exit a game and pick a different game. Then both event handlers will be running and writing to the screen. Is there not an unsubscribe option for register_frame_done? What option do I have here? I guess declaring register_frame_done only once outside of add_machine_reset_notifier is the only option I can see at the moment.

[cuavas]

You don’t want to keep registering additional handlers, and you want to clean up anything tied to the machine when it exits.

The way you have that code, you'd register an additional handler each time the user does an F3 reset even if they never start another machine.

[Jakobud]

Yes I have finally realized that thank you.

Just to verify, there is no way to unsubscribe from the emu.register_frame_done function correct?

[cuavas]

Just to verify, there is no way to unsubscribe from the emu.register_frame_done function correct?

Correct, one of the major limitations of those emu.register_xxx functions is that you can’t unsubscribe.

[Jakobud]

When you use emu.register_start when you load up a game then exit and load another game, etc.. are you just creating more and more event handlers that are running in the background?

I'm just writing a plugin that it would be nice if it was a little bit backwards compatible so I'm curious.