IR-Remote | Simple Android IR-Remote for my Samsung TV and Soundbar | Android library

I'm not going to rewrite your program to make it multi-threaded as that's behind the scope of answering a specific question. I can give you a description of what's required though as a starting point.

First of all, a simpler way to fix this without threads would be to use something like signals to stop the playing of the tune. This is what happens when you press Ctrl-C. Your program is reading input from your IR though, so as far as I can tell using threads looks necessary to both reading IR input and playing of sound happen at the same time.

I'm not familiar with Arduino but I'm assuming you have something like pthreads. You would need to get familiar with that. It is not a trivial change as using threads is very different paradigm and takes time to get your head around if you haven't used them before. The main thing to get your head around is that code is executing in more than one place.

Your main thread, the beginning process before any thread is created, would be running loop() so it can respond to any IR input. Having it in its own thread lets it respond to any user input. The problem with your code right is that it must wait for the playing of the tune in playSuperMario() to return before it can process any new input.

You would create a thread somewhere during initialization. This thread will be what plays the tune. It needs to be able to start the tune based on IR input. Also you'll need to define the behavior of things like what happens if the "ON" button is pressed while it's already playing? Does it start again, stop or is that ignored and it keeps playing?

You'll need one or more variables used by both threads. This will require mutex protection so only one thread can read/write it at a time. Let's say there's a global variable isPlaying initially set to true. When the off button is pressed this would be changed to false. Your playSuperMario() and buzz(), etc. functions would need to check if this value is false in its loops. If false then it will return immediately.

That's a general pointer to how to handle this hope it helps.