Question

I have one doubt. I implemented my wcf 4.0 service method as shown below.

    IAsyncResult BeginGetData(string userid, AsyncCallback cb, object asyncState)
    {
       // Here i want to call 2 different methods simultaneously of another class

       // string result1 = classA.Method1(userid);
       // string result2 = classA.Method2(userid);        

    }

How I can call 2 methods simultaneously and both result values send back to client in the same return method ? Can we do it using TPL ? In TPL, if we use Task.ContinueWith, it will run sequentially. Is there any way that run those 2 methods parallely and return the 2 results through the EndGetData method ? If Method1 is completing first, then it should wait for Method2 to complete. Or another way is to fireback each method result as and when they completed. Is this possible ? Please help and guide me.

Answer 1

I am not sure about the intracacies of using WCF to do all of this for you. However, here you can just use Task Parallel Library’s (TPL) ContinueWhenAll keyword:

An example of its usage is

Task task1 = Task.Factory.StartNew(() => Console.WriteLine("X"));
Task task2 = Task.Factory.StartNew(() => Console.WriteLine("Y"));

this fires the two task off concurrently on two seperate background thread-pool threads. You can then wait for both to finish using

var continuation = Task.Factory.ContinueWhenAll(
    new[] { task1, task2 }, tasks => Console.WriteLine("Done!"));

Or here, you could also use the WhenAll task combinator and write

var continuation = Task.WhenAll(task1, task2)
    .ContinueWith(ant => Console.Writeline("Done!"));

Example in your case of returning data from the tasks:

Task<int> task1 = Task.Factory.StartNew<int>(() => 
    { 
        return SomeSerialMethodReturningInt32A(); 
    });
Task<int> task2 = Task.Factory.StartNew<int>(() => 
    { 
        return SomeSerialMethodReturningInt32B(); 
    });

then in the continuation (what ever method of continuation you choose), you can query the results (and remember to observe your AggregateExceptions) as follows

var continuation = Task.Factory.ContinueWhenAll(
    new[] { task1, task2 }, tasks => 
        { 
            int i = task1.Result;
            int j = task2.Result;
            // Neglecting exception handling.
        });

See this CodeProject article for a great introduction to TPL.

I hope this helps.