Calling WCF Services asynchronously using async and await

 

In my previous post, I covered how to use async and await keywords in C# 5 to create asynchronous methods. This post is a continuation of asynchronous programming, in which I will cover how to call WCF services from a client program using async and await.

Response of an application will be slower when it includes heavy weight operations like running complex queries against database, reading a piece of data from a file, calling a service to get some data or any remote operation. When such operations are performed synchronously, the application will be halted till the operation gets over. If we assign the slower operation to a separate task, the thread will be free to perform some other operation till the operation responds.

When a WCF service is called synchronously, the thread associated with the operation is idle till the response is obtained from the server. To avoid this in earlier versions of .NET framework (4.0 or earlier), we had an option to create asynchronous methods with an associated event. Using .NET 4.5, we can create task-based proxies while adding service reference to an application. This can be done using by clicking on the Advanced button in the Add Service Reference dialog.

To call a WCF service synchronously, you can simply use the proxy method created by the Visual Studio, similar to calling a local method.

To call a WCF service asynchronously, you will need to first create an "AsyncCallback" "delegate" and pass this delegate to the asynchronous proxy method generated by the Visual Studio. Since the "AsyncCallback" "delegate" is executed in a worker thread different from the UI thread, any access to the "UI elements" needs to be "Dispatched".

From the application point of view, either way has its advantages and disadvantages. For most applications, after the calling of a WCF service, the application will be in an intermediate state until the response from the service is received. During this time, it may be ideal to block the UI thread to prevent user actions to get into any un-predictable results. In this case, a synchronous call may be appropriate. In some other scenarios, particularly when we work on some "SOA" applications, we may need to make multiple service calls at the same time and let the services to work in parallel. In this case, asynchronous WCF calls will be the ideal.

One thing just came to my mind. To make an asynchronous call, you probably do not need to have the asynchronous proxies. You can well fork a worker thread by yourself and let the thread to do a synchronous call. You will achieve the same effect as using the asynchronous proxies.

If you are not familiar with WCF services, this link is a good place to get you started.