Async Action Methods

Question

I was looking at ASP.NET MVC 5 templates and I have notice that many of the actions and marked as async:

public async Task<ActionResult> Login(LoginViewModel model, string returnUrl) { }

When should I do this on an MVC action? When it contains access to a database?

If I call a repository inside the action should I also use Task to make it async?

Answer 1

The core of your questions is: When should I make my MVC actions async? See http://blogs.msdn.com/b/rickandy/archive/2009/11/14/should-my-database-calls-be-asynchronous.aspx for a good discussion of the issue. He talks about the database only, but his points carry over.

Essentially, almost never call the database in an async way.

For database applications using async operations to reduce the number of blocked threads on the web server is almost always a complete waste of time.

Don't be detracted by people telling you to always use async IO if possible. Async is all the rage right now. Lot's of irrational advice is being spread.

Answer 2

Entity Framework 6 (used by default with MVC 5) now supports async database calls, so the action method signatures have been update to reflect async being used. The simple answer is that whenever you have a task that could potentially involve waiting, use async. Hopefully, your database queries won't take long enough to roundtrip to actually benefit much from async, but if your database falls down or is being hammered particularly hard, it'll at least help to not deadlock IIS in the process.