CODEWITHSUNDEEP
asp.net-mvcasp.net-mvc-5async-await
Miguel Moura
Miguel Moura

Reputation: 39354

Async Action Methods

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?

Upvotes: 17

Views: 16789

Answers (3)

user3285954
user3285954

Reputation: 4729

Here's an article what lists some uses cases when using tasks may have benefit and some uses cases when may have the opposite effect. The answer is not this simple every time, this is why the last point about testing.

Quote from http://www.asp.net/mvc/overview/performance/using-asynchronous-methods-in-aspnet-mvc-4

In general, use synchronous methods for the following conditions:

  • The operations are simple or short-running.
  • Simplicity is more important than efficiency.
  • The operations are primarily CPU operations instead of operations that involve extensive disk or network overhead. Using asynchronous action methods on CPU-bound operations provides no benefits and results in more overhead.

In general, use asynchronous methods for the following conditions:

  • You're calling services that can be consumed through asynchronous methods, and you're using .NET 4.5 or higher.
  • The operations are network-bound or I/O-bound instead of CPU-bound.
  • Parallelism is more important than simplicity of code.
  • You want to provide a mechanism that lets users cancel a long-running request.
  • When the benefit of switching threads out weights the cost of the context switch. In general, you should make a method asynchronous if the synchronous method waits on the ASP.NET request thread while doing no work. By making the call asynchronous, the ASP.NET request thread is not stalled doing no work while it waits for the web service request to complete.
  • Testing shows that the blocking operations are a bottleneck in site performance and that IIS can service more requests by using asynchronous methods for these blocking calls.

Upvotes: 5

usr
usr

Reputation: 171178

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.

Upvotes: 11

Chris Pratt
Chris Pratt

Reputation: 239220

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.

Upvotes: 9

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