Sony Arouje

a programmer's log

Posts Tagged ‘Asynchronous call

Using await in real world asynchronous programming–Part 2

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This is the continuation to my previous post related to new async ctp. In the previous post I explained the use of await using a webclient. This post I am going to explain how can we use await in real life scenario. In real life you may not only deal with webclient, you may wanted to do a time consuming database call or you wanted to do some time consuming process or whatever in asynchronous manner, at the same time our UI should be responsive.

I did a lot of search to find a scenario to deal expensive process other than calling a webclient but no use. So I thought it will be good to post some real life scenario as most of the blogs explain the async ctp with webclient or in some complex way that person like me cant understand.

Async CTP simplify the way we write asynchronous methods, with async ctp no BeginXXX and no EndXXX. So let’s go through the scenario with a small intro.

Currently am in the process of rewriting one of my app called iTraveller. My prime focus is a very responsive UI with less app loading time. The app requires to load categories and lot of thumbnails at startup. I am doing lot of these process at startup and if we do it synchronously it will affect the application startup speed. When async CTP launched, I jumped into to it, because I know that it’s very useful for me.

Below is a piece of code we normally write to load some data from a database.

public List<LocalCategory> GetAllCategories()
    IRepository repository = GenericRepository.GetRepositoryInstance();
    return repository.GetAll<LocalCategory>().ToList<LocalCategory>();


Here I used the Generic repository model I explained earlier in my blog. The above method is a synchronous call and the caller should wait till the db calls complete. Am going to rewrite the above method in async mode.

public async Task<List<LocalCategory>> GetAllCategoriesAsync()
    IRepository repository = GenericRepository.GetRepositoryInstance();
    return await TaskEx.Run(() => 
        //write the time consuming process here
        return repository.GetAll<LocalCategory>().ToList<LocalCategory>();
    }, System.Threading.CancellationToken.None);


Here I converted a synchronous method to an asynchronous one, It’s as simple as that. Let’s see how can we call the above method.

private async void LoadExistingCategory()
    CategoryService categoryService = new CategoryService();
    var categoriesTask=await categoryService.GetAllCategoriesAsync();
    this.ExistingCategories = categoriesTask.ToList<LocalCategory>();


You can call the async method in button event handler or where ever you want to call. But the caller should marked as async, the above method I added async just after the private.

LocalCategory is one of my entity class in the application.

I wrote a very expensive Euclidean distance algorithm using async mode and it worked very well. The same without async will keep the UI busy for two seconds and the user will be blocked from doing any action. 

Written by Sony Arouje

December 9, 2010 at 11:20 pm

Proxy less Silverlight – WCF Async communication

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In this post I am going to explain how a silverlight application can communicate with WCF service without any proxy. I wanted to establish this communication without any autogenerated code because am not a fan of proxies generated by VS. If you want VS to create good autogenerated code then probably invest some time in learning T4 templates. Anyway I haven’t done any research in T4 templates, so let’s do every thing by hand.

Here is my requirement, I have to show a list of customer in my Silverlight app. Keep in mind it just an experiment, so no db involved in this app. For simplicity I hosted my wcf service in IIS.

Let’s straight to the code.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.ServiceModel;
using DataModel;
namespace ServiceContracts
    public interface ICustomerService
        ICollection<Customer> GetCustomerList();


I only have one function in the service contract, a function return a collection of Customer class. Customer class is a just a C# class that has only two properties as shown below

using System.Runtime.Serialization;
namespace DataModel
    public class Customer
        public int CustomerId { get; set; }

        public string CustomerName { get; set; }
Let’s give some implementation to our Service Contract
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using ServiceContracts; //assembly consist service contracts
using DataModel; //assembly contains data contracts
namespace ServiceLayer
    public class CustomerService:ICustomerService
        public ICollection<Customer> GetCustomerList()
            List<Customer> customers = new List<Customer>();
            Customer cust = new Customer();
            cust.CustomerId = 1;
            cust.CustomerName = "sony";

            return customers;




Now our service is ready to host, here I use IIS to host it. But how does Silverlight can utilize the Function we implemented, because I haven’t implemented Async methods. You might know that Silverlight can only work in Async mode. There are several ways of calling the above implemented service in Silverlight. One way is adding Service reference and leave it to VS to create the proxy with Async code generation. Another approach is use Castle Windsor to host the service in Async mode. Some how I didn’t like both the approach so I was trying for a better approach. My search ended up in a blog to achieve the Async communication without much modification to my Service code.

Here is the approach I was looking at. Create a new Service contract with Async functions and make it an alias to my original ICustomerSerivce

[ServiceContract(Name = "ICustomerService")]
public interface ICustomerServiceAsync
    [OperationContract(AsyncPattern = true)]
    IAsyncResult BeginGetCustomerList(AsyncCallback callback, object state);

    ICollection<Customer> EndGetCustomerList(IAsyncResult result);


And use the above ICustomerServiceAsync to communicate to ICustomerService. This approach is pretty clean and we don’t want to add any Async methodology to our core service.

Below is my web.config of WCFService host.

<?xml version="1.0"?>

    <compilation debug="true" targetFramework="4.0" />
      <service name="CustomerService">
        <endpoint address="" contract="ServiceContracts.ICustomerService" binding="basicHttpBinding"></endpoint>
          <!-- To avoid disclosing metadata information, set the value below to false and remove the metadata endpoint above before deployment -->
          <serviceMetadata httpGetEnabled="true"/>
          <!-- To receive exception details in faults for debugging purposes, set the value below to true.  Set to false before deployment to avoid disclosing exception information -->
          <serviceDebug includeExceptionDetailInFaults="true"/>
    <serviceHostingEnvironment multipleSiteBindingsEnabled="true" />
    <modules runAllManagedModulesForAllRequests="true"/>


As you see my service end point configuration I have not mentioned ICustomerServiceAsync. Let’s go through the silverlight client how we can communicate to our service.

private void button1_Click(object sender, RoutedEventArgs e)
    EndpointAddress endPoint = new EndpointAddress("http://localhost:63301/CustomerService.svc");
    BasicHttpBinding binding = new BasicHttpBinding();
    ICustomerServiceAsync customerService = new ChannelFactory<ICustomerServiceAsync>(binding, endPoint).CreateChannel();

    customerService.BeginGetCustomerList(a => 
            ICollection<Customer> person = customerService.EndGetCustomerList(a);
        catch (Exception ex)
            throw ex;

    }, customerService);


In a button click am calling the service.  Here I used the ICustomerAsync to create the channel. Ayende’s blog will give you more details.

You might think how I could able to reference ICustomerServiceAsync and Customer classes in my Silverlight client. What I did here is I created a Silverlight class library and add ICustomerAsync and Customer class as a link. In VS we can do it by selecting add existing item and rather than clicking on the Add button, click on the arrow on the right side of the Add and select as link from the option.

In the above client code I used lambda expression to call the service. You can also use a anonymous delegate or Callback method to achieve the same.

One important thing you need to add to our WCFService host project is clientaccesspolicy.xml, other wise Silverlight client will not be able to communicate and throws Security exception. Below is the policy file

<?xml version="1.0" encoding="utf-8"?>
      <allow-from http-request-headers="*">
        <domain uri="*"/>
        <resource path="/" include-subpaths="true"/>


To test my connection and exceptions I used a Winform application. Silverlight wont give proper error details.

Download the code here



Written by Sony Arouje

October 1, 2010 at 7:14 pm

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