Function omnisensor::threshold::get_prop_value

fn get_prop_value<F, R>(
    ctx: PropContext,
    sensor: &Arc<Mutex<Sensor>>,
    sev: ThresholdSeverity,
    getter: F
) -> impl Future<Output = PhantomData<R>>where
    F: Fn(&Threshold) -> R,
    R: Arg + RefArg + Append + 'static,

Retrieve a threshold property value from the given sensor for the given severity sev via getter, sending it back over dbus via ctx.