Async WCF web-Services

In the world of Scalable programming, it’s all about Event Driven or Asynchronous programming. Event driven, callback based programming like node.js have taken the programming world by storm and few .NET based open source Event driven servers like KayakHttp (OWIN) have it’s uses but when it comes to Asp.NET MVC or WCF, asynchronous programming can be achieved using Tasks based programming approach. Do remember that Asynchronous programming model requires a good data access/interaction system design. A good async design can provide better scalability and potentially high server throughput. NOTE: higher throughput is server handling more requests and not speedier execution (some cases, yes)

A WCF service having async operations can provide a higher server throughput since the server is not longer waiting for the operation to complete to serve the next request. Off-course an Async design pattern adds complexity to the system. Following is how to provide a async operation:

Step 1, in the service interface we need to let the OperationContract know it’s a async operation



Step 2 is make the function call Async by providing a Begin and End operation. Basically Begin method is called when operation starts and End Method is the callback function when the operation completes execution. Following is the same function as above but with Begin and End




Step 3, once the operations are modified with Begin and End methods in the Service Interface, we need to build out the functions in the actuall Service Class.




In BeginGetData function, a new async Task is spawned with a return value of “string” and once the method “GetData” is executed the callback function is called. Task.ContinueWith is trigged only once the value is returned or if there is any unhandled exception thrown. In EndGetData function, basically takes the result and returns back to the calling client.

An example of calling client:




To learn more about Tasks, MSDN should be a good starting point [http://msdn.microsoft.com/en-us/library/system.threading.tasks.task.aspx]