How do I continue working on the server after returning a response with ASP.NET? (WebForms and MVC)

Question

I have an application where I need the user to upload a photo. After the photo is uploaded to the server, which shouldn't take very long, the user should get back a response that's a regular HTML page saying "thanks...bla bla bla..."
Now, after the the response is sent back to the client and he goes on his merry way, I want the server to continue to work on this photo. It needs to do something that's heavy and would take a long time. But this is okay because the user isn't waiting for anything. He's probably in a different page.
So my question is, how do I do this with ASP.NET. The application I'm writing is in ASP.NET MVC so I'm imagining something like

//save the photo on the server
//and send viewdata saying "thanks..."
return View();
//keep doing heavy processing on the photo

But I guess this isn't really how it's done. Also, since sometimes I work with ASP.NET WebForms, how is this done with WebForms as well.
Thank you!

Answer 1

We do this for a lightweight logging situation:

Action<object> d = delegate(object val)
{
    // in this anonymous delegate, write code that you want to run
    ProcessDataAndLog();
};

d.BeginInvoke(null, null, null); // this spins off the method asynchronously.

It's by no means robust. If you need a guarantee of being processed you should consider a message queue. That way you can also offload processing to a separate machine and not bog down your web server.

EDIT:

The following also works, and is perhaps a little more obvious to your fellow coder. It's essentially the same, but apparently faster and you don't need to worry about calling EndInvoke().

System.Threading.ThreadPool.QueueUserWorkItem(
    delegate(object state)
    {
        // in this anonymous delegate, write code that you want to run
        ProcessDataAndLog();
    });

Further Reading: The Thread Pool and Asynchronous Methods and Asynchronous delegate vs thread pool & thread and Does not calling EndInvoke really cause a memory leak ?

Answer 2

It seems to me like you need to spin off another process to do what you need to do. You might even want to build a windows service to handle the processing of the image. It could be an app that sits around waiting for a file to appear somewhere, and when it does it can go to work leaving the asp.net thread to go about its business.