Asynchronous web service call in ASP.NET/C#

Yes, what you're describing is async processing.

The best solution depends to some degree on the nature of the web services call and how you want to handle the results. A few tips that might help:

1. One approach is to send a request from the initial web request to a background thread. This works best if your users don't need to see the results of the call as soon as it completes.
2. Another approach is to have your server-side code make an async web services call. This is the way to go if your users do need to see the results. The advantage of an async call on the server side is that it doesn't tie up an ASP.NET worker thread waiting for results (which can seriously impair scalability)
3. Your server-side code can be structured either as a web page (*.aspx) or a WCF service, depending on what you want to have it return. Both forms support async.
4. From the client, you can use an async XMLHTTP request (Ajax). That way, you will receive a notification event when the call completes.
5. Another approach for long-running tasks is to write them to a persistent queue using Service Broker. This works best for things that you'd like users to be able to start and then walk away from and see the results later, with an assurance that the task will be completed.

In case it helps, I cover each of these techniques in detail in my book, along with code examples: Ultra-Fast ASP.NET.

If you're not blocking for a method return you're doing asychronous processing. Have a look at Dino Esposito's article on using AJAX for server task checking.

You can perform asynchronous web service calls using both Web Service Enhancements (WSE) and Windows Communication Foundation (WCF) in your C# code. WSE is discontinued, so its use is not recommended. Generically speaking, if you were to terminate program execution in the middle of an asynchronous call before the response returned, nothing bad would happen; the client would simply not process the result, but the web service would still be able to perform its processing to completion.

If your client web application is responsible for updating the DB, then without anything else in your client code, quitting in the middle of an asynchronous operation would mean that the DB was not updated. However, you could add some code to your client application that prevented the browser from quitting entirely while it is waiting for an asynchronous response while preventing new web service calls from being run after Close is called (using Javascript).

You have 2 distinct communications here: (1) from web browser to web application and (2) from web application to web service.

diagram http://img697.imageshack.us/img697/6713/diagramo.png

There is no point of making (2) asynchronous: you still would have to wait for web service to finish processing request. If you end HTTP request from browser to web application the client would have no clue what the result of request was.

It is much better to make asynchronous request from web browser to your web application. Ajax is ideal for that. In fact, that's what it was created for. Here's couple of links to get you started:

• jQuery Ajax
• ASP.NET AJAX