Parallel Work in Async MVC Actions

public async Task<ActionResult> Index(string city)
{
    var newsService = new NewsService();
    var sportsService = new SportsService();

    return View("Common",
        new PortalViewModel
        {                    
            NewsHeadlines = await newsService.GetHeadlinesAsync(),
            SportsScores = await sportsService.GetScoresAsync()                    
        });
}    

public async Task<ActionResult> Index(string city)
{
    return View("Common",
        new PortalViewModel
        {                    
            NewsHeadlines = await GetHeadlinesAsync(),
            SportsScores = await GetScoresAsync()      
        });
}
async Task<IEnumerable<Score>> GetScoresAsync()
{
    await Task.Delay(3000);
    // return some scores ...
}
async Task<IEnumerable<Headline>> GetHeadlinesAsync()
{
    await Task.Delay(3000);
    // return some news
}

In the methods I’ve introduced a delay using Task.Delay (which returns a Task you can await and thereby free the calling thread, unlike Thread.Sleep which will block). The total time to render the view will be at least 6,000 milliseconds, because the Index action awaits the result of GetHeadlinesAsync. Awating will suspend execution before GetScoresAsync has a chance to start.

If you want the headlines and scores to work in parallel, you can kick off both async calls before awaiting the first result.

public async Task<ActionResult> Index(string city)
{
    var newsService = new NewsService();
    var sportsService = new SportsService();

    var newsTask = newsService.GetHeadlinesAsync();
    var sportsTask = sportsService.GetScoresAsync();

    return View("Common",
        new PortalViewModel
        {

            NewsHeadlines = await newsTask,
            SportsScores = await sportsTask
        });
}