Improving CPU usage

One issue you may have noticed is that when no song is playing, the software will use 100% of the CPU. This is because of the infinite loop in the music engine thread. It will do nothing except loop when the song is paused or when there's no song to play. Let's now fix this issue.

Condition variable

What we want to do is to make the thread sleep when it has nothing to do. We also want to be able to wake the thread up from the main thread. This is exactly what condition variables are for. So, let's add one to our engine. We'll start by adding a condition_variable field to the EventLoop:

struct EventLoop {
    condition_variable: Arc<(Mutex<bool>, Condvar)>,
    queue: Arc<SegQueue<Action>>,
    playing: Arc<Mutex<bool>>,
}

A condition variable is usually used together with a Boolean value (wrapped in a Mutex). We need to rewrite the constructor of EventLoop to initialize this new field:

impl EventLoop {
    fn new() -> Self {
        EventLoop...