Returning a view with async keyword

Question

There are some code samples where I show some code like below.

 public async Task<IActionResult> AddUser(User user)
 {
      ///Logic to add user
      return View();
 }

Is this a good practice to return a view with async action result method as view result it self-does not support async.

I checked in normal scenarios it works perfectly fine but what are the scenarios where it might fail or create problems.

Answer 1

The use of async and await is a good practice to make your web application scalable, said MSDN (if I remember correctly :)). Basically, it helps utilizing your thread pool so that 1 thread does not necessarily to be allocated to handle only 1 request. Suppose that you have this action:

 public async Task<IActionResult> AddUser(User user)
 {
      ///Logic to add user
      return await Task.Run(() => View());
 }

it's being said that while waiting for the async method to be completed, the thread will be available to be allocated for another work item (e.g another action marked as async) in the .NET run-time thread-pool global queue. This makes the number of threads can be less than the number of requests need handling.

The async modifier is marked to tell .NET run-time that this is a work item that can be applied mechanism mentioned above. Without await something, it doesn't help much (if we don't want to say "nothing") in terms of performance or resource optimization.

For proof of concept, I played with following actions in my HomeController:

    public async Task<ActionResult> FineGrained()
    {
        return await Task.Run(() => {
            return Json(Thread.CurrentThread.ManagedThreadId, JsonRequestBehavior.AllowGet);
        });
    }

    public async Task<ActionResult> CoarseGrained()
    {
        return await Task.Run(async () => {
            await Task.Delay(TimeSpan.FromSeconds(5));
            return Json(Thread.CurrentThread.ManagedThreadId, JsonRequestBehavior.AllowGet);
        });
    }

and this is the jquery script to test the thread utilization:

        $.when(
            $.getJSON('/Home/FineGrained'),
            $.getJSON('/Home/CoarseGrained'),
            $.getJSON('/Home/FineGrained'),
            $.getJSON('/Home/FineGrained'),
            $.getJSON('/Home/FineGrained')
        ).done(function (v1, v2, v3, v4, v5) {
            console.log(v1[0]);
            console.log(v2[0]);
            console.log(v3[0]);
            console.log(v4[0]);
            console.log(v5[0]);
        });

One of many results I got: 30 25 30 30 25

I refreshed the page containing the test script several times and always got repeat thread id. It's fair enough to prove the theory.