How to process long running requests with an HTTP handler under IIS?

Question

I need to process long running requests inside IIS, handling the request itself is very lightweight but takes a lot of time mostly due to IO. Basically I need to query another server, which sometimes queries a third server. So I want to process as many requests as I can simultaneously. For that I need to process the requests asynchronously how do I do that correctly?

Using the Socket class I could easily write something like :

// ..listening code
// ..Accepting code

void CalledOnRecive(Request request)
{
    //process the request  a little
    Context context = new Context()
    context.Socket  = request.Socket;
    remoteServer.Begin_LongRunningDemonicMethod(request.someParameter, DoneCallBack, context);
}

void DoneCallBack( )
{
    IAsyncresult result = remoteServer.Begin_CallSomeVeryLongRunningDemonicMethod( request.someParameter, DoneCallBack, context);

    Socket socket = result.Context.Socket;
    socket.Send(result.Result);
}

In the example above the thread is released as soon as I call the "Begin..." method, and the response is sent on another thread, so you can easily achieve very high concurrency . How do you do the same in an HTTP handler inside IIS?

Answer 1

You can implement an HttpHandler with IHttpAsyncHandler. MSDN has a nice walkthrough with examples on how to do that here.

Answer 2

Start with something like this:

public class Handler : IHttpAsyncHandler {
    public void ProcessRequest(HttpContext context)
    {
    }

    public IAsyncResult BeginProcessRequest(HttpContext context,
            AsyncCallback cb, object extraData)
    {
        IAsyncResult ar = BeginYourLongAsyncProcessHere(cb);
        return ar;
    }

    public void EndProcessRequest(IAsyncResult ar)
    {
        Object result = EndYourLongAsyncProcessHere(ar);
    }

    public bool IsReusable { get { return false; } }
}

If you need to chain multiple requests together, you can do so in an async HttpHandler, but it's easier if you use an async Page.