Using async await inside the timer_elapsed event handler within a windows service

Question

I have a timer in a Windows Service, and there is a call made to an async method inside the timer_Elapsed event handler:

protected override void OnStart(string[] args)
{
     timer.Start();    
}  

private async void timer_Elapsed(object sender, ElapsedEventArgs e)
{
    _timer.Stop();
    await DoSomething();          
    _timer.Start();
}

Is the above code ok? Firstly, I have read that async void is not a good idea. Secondly, why would I need the timer_Elapsed method to be async in the first place? It's not like the elapsed event handler us going to get called in parallel by multiple callers. However, if I don't make the method async, then my logic will break because timer will start before DoSomething completes.

So, is making timer_Elapsed async the correct approach?

Answer 1

Async void should be avoided; it should only be used for event handlers. Timer.Elapsed is an event handler. So, it's not necessarily wrong here.

The timer_Elapsed method has to be async because it contains an await. This is the way the keywords work: async rewrites the method as an asynchronous state machine, which enables the await keyword.