Question

I’ve read up on the Async Page and it’s usage, looks simple:

[UPDATE] Taken from here:

protected override void OnInit(EventArgs e)
{
    base.OnInit(e);

    var task = new PageAsyncTask(BeginRequest, EndRequest, null, null);
    RegisterAsyncTask(task);
}

IAsyncResult BeginRequest(Object sender, EventArgs e, 
                          AsyncCallback cb, object state)
{ 
    return _service.BeginHelloWorld(cb);
}

void EndRequest(IAsyncResult asyncResult)
{
    var answer = _service.EndHelloWorld(asyncResult);
    // do something with answer
}

But I can’t get my head around the following problem:

What if I want to call an asynchronous operation/webservice from my business layer and not directly from my page’s code-behind? I can’t seem to find any info on that on the net.

The scenario in a nutshell:

Request –> Page handler –> Business layer service – || -> External webservice

One solution to the problem I can think of would be to call the business layer service asynchronously, utilizing a second thread from the thread pool only for the amount of time needed to call the external webservice:
Request –> Page handler – || -> Business layer service – || -> External webservice. [UPDATE ->] So basically I thought of extending the above approach to my business layer service using the exact same pattern. [<- END]
In this case, both threads would be released to the thread pool (or so I guess) and could process other incoming requests. When the answer from the webservice returns, at first a thread is bound for processing the business layer service and then another for finishing the Page rendering. But that sounds like a lot of overhead – both in coding and maybe even at runtime.

Another solution would be a modification of the first one – namely, returning an unfinished response to the client once we trigger the external webservice call and processing the result of it not in the context of a Request but simply inside the application. Then, of course, the client would have to poll the server for the result which should have been saved somewhere. This is basically the idea that @emfurry layed out in Async Web Service Calls.

Are there any other viable options I have not considered?

Answer 1

You could consider taking a look at messaging or the use of a service bus.

I have a FOSS ESB here: http://shuttle.codeplex.com/

This allows you to do asynchronous processing.