Timeout operation with .NET CancellationTokenSource

CancellationTokenSource.cs

async Task Main()
{
  var sw = new Stopwatch();
  sw.Start();
  var cts = new CancellationTokenSource(TimeSpan.FromSeconds(3));
  await Foo(cts.Token);
  sw.Stop();
  Console.WriteLine("Elapsed " + sw.ElapsedMilliseconds);
}

async Task Foo(CancellationToken ct)
{
  while (true)
  {
    if (ct.IsCancellationRequested)
    {
      return;
    }

    await Task.Delay(200);
  }
}