C# Silverlight WCF: Thread Safe Multiple Async Call Strategy With Final Operation To Join Data.

This article describes one way to handle asynchronous or async calls in .Net 3.5 or .Net 4.0 when using WCF in Silverlight in C#. The goal is to have a final operation wait for all the calls to finish so to combine all the data gathered, all in a thread safe way. A secondary goal is to minimize the consumer code required to perform this operation from what is currently available in straight WCF async calls.

This article has a short shelf life because after .Net 4 (see What’s Next in C#? Get Ready for Async!) one will use the built in Asynchrony methodology developed. Until that time if one is using any version of Silverlight and WCF then this article describes how to handle those multiple async calls and join the data in a final method call.

Final Result Example

Before delving into the solution, here is how the consumer will use the methodology. Below a user is getting account information of user requests, departments and accounts to join all the data on the view model in the final method for display on a Silverlight page. Thesee operations as shown are setup when the view model class (MyViewModel) is created and no blocking occurs keeping UI thread clear.

public MyViewModel()

{

    DataContext = new MyServiceClient();

 

    FinalAsync(CombineDataAndDisplay); // When all the data is retrieved, do this method to combine the data From the 3 async callls below

 

    // Provide the operation as a lambda (could be a method call) to assign data to our target backing store property

    // and if all has gone well (no errors in other async calls) and it is the final completing operation. Do the final

    // Processing call automatically.

    DataContext.GetUserRequestsCompleted   += (s, e) => { AssignResultCheckforAllAsyncsDone(e, e.Result, ref _UserRequests, "Acquisition failure for User Requests");};

    DataContext.GetAccountsCompleted       += (s, e) => { AssignResultCheckforAllAsyncsDone(e, e.Result, ref _Accounts, "Acquisition Failure for Accounts"); };

    DataContext.GetDepartments             += (s, e) => { AssignResultCheckforAllAsyncsDone(e, e.Result, ref _Departments, "Failed to get Department Info."); };   

 

    // Start the Async processes

    MultipleAsyncRun(DataContext.GetUserRequestsAsync);

    MultipleAsyncRun(DataContext.GetAccountsAsync);

    MultipleAsyncRun(DataContext.GetDepartmentsAsync);

 

    // Exit out and return the UI thread to the user operations.

}

 

// Once all the data is done, combine and assign into our

// PagedCollectionView property for display on the screen.

public void CombineDataAndDisplay()

{

    // Combine missing data on the calls

   _UserRequests.ToList()

                .ForEach(ur =>

                {

                ur.BillingName     = _Accounts.First(ac => ur.AccountID == ac.AccountID).Name;

                ur.DepartmentName  = _Departments.First(dp => dp.DepartmentID == ur.DepartmentID).Name;

                });

 

    UserRequests = new PagedCollectionView( _UserRequests);

    UserRequests.GroupDescriptions.Add(new PropertyGroupDescription("DepartmentName"));

 

}

Read more: OmegaMan's Musings Technology blog written by a Microsoft C# MVP

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