Performing an async operation before every action in a controller

Question

Consider the following:

public class FooController : Controller
{
    public async Task<ActionResult> Foo()
    {
        await DoSomethingAsync();

        ...

        return View();
    }

    public async Task<ActionResult> Bar()
    {
        await DoSomethingAsync();

        ...

        return View();
    }

    ...
}

This line, await DoSomethingAsync(); is repeated for each action in the controller. It'd be much nicer to do something like:

public override void OnActionExecuting(ActionExecutingContext filterContext)
{
    await DoSomethingAsync();
}

But, obviously, you can't run an async op in a synchronous method. I could simply force the async op to run sync, but then you end up with the thread being blocked unnecessarily. Short of running this sync, what options do I have?

Have you seen this: aspnetwebstack.codeplex.com/discussions/478983 — David Tansey
– David Tansey, Commented Jul 31, 2014 at 20:03

Stephen Cleary · Accepted Answer · 2014-07-31 20:06:33Z

1

Unfortunately, ASP.NET MVC does not have asynchronous filters today. ASP.NET WebAPI does have them, and ASP.NET vNext (combining MVC and WebAPI) does have them.

So, for today I'd say you're best off repeating the code, but in the future (near future, hopefully) that could be cleaned up.

answered Jul 31, 2014 at 20:06

Stephen Cleary

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2 Comments

Chris Pratt Over a year ago

I'm accepting this as it's technically correct, but the link @DavidTansey posted in the comments below my question gave me a workaround.

Stephen Cleary Over a year ago

I completely disagree with both of those workarounds. The entire point of async on ASP.NET is to free up a thread, and the workaround on codeplex uses an extra thread instead. If you absolutely must do it, then OK, but I'd prefer to just use synchronous methods instead.

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