How to: Call Operations Asynchronously Using a Channel Factory

Article
05/04/2023

This topic covers how a client can access a service operation asynchronously when using a ChannelFactory<TChannel>-based client application. (When using a System.ServiceModel.ClientBase<TChannel> object to invoke a service you can use the event-driven asynchronous calling model. For more information, see How to: Call Service Operations Asynchronously. For more information about the event-based asynchronous calling model, see Event-based Asynchronous Pattern (EAP).)

The service in this topic implements the ICalculator interface. The client can call the operations on this interface asynchronously, which means that operations like Add are split into two methods, BeginAdd and EndAdd, the former of which initiates the call and the latter of which retrieves the result when the operation completes. For an example showing how to implement an operation asynchronously in a service, see How to: Implement an Asynchronous Service Operation. For details about synchronous and asynchronous operations, see Synchronous and Asynchronous Operations.

Procedure

To call WCF service operations asynchronously

Run the ServiceModel Metadata Utility Tool (Svcutil.exe) tool with the /async option as shown in the following command.
```
svcutil /n:http://Microsoft.ServiceModel.Samples,Microsoft.ServiceModel.Samples http://localhost:8000/servicemodelsamples/service/mex /a
```
This generates an asynchronous client version of the service contract for the operation.

Create a callback function to be called when the asynchronous operation is complete, as shown in the following sample code.

static void AddCallback(IAsyncResult ar)
{
    double result = ((CalculatorClient)ar.AsyncState).EndAdd(ar);
    Console.WriteLine("Add Result: {0}", result);
}

Private Shared Sub AddCallback(ByVal ar As IAsyncResult)
    Dim result = (CType(ar.AsyncState, CalculatorClient)).EndAdd(ar)
    Console.WriteLine("Add Result: {0}", result)
End Sub

To access a service operation asynchronously, create the client and call the Begin[Operation] (for example, BeginAdd) and specify a callback function, as shown in the following sample code.

ChannelFactory<ICalculatorChannel> factory = new ChannelFactory<ICalculatorChannel>();
ICalculatorChannel channelClient = factory.CreateChannel();

// BeginAdd
double value1 = 100.00D;
double value2 = 15.99D;

IAsyncResult arAdd = channelClient.BeginAdd(value1, value2, AddCallback, channelClient);
Console.WriteLine("Add({0},{1})", value1, value2);

Dim factory As New ChannelFactory(Of ICalculatorChannel)()
Dim channelClient As ICalculatorChannel = factory.CreateChannel()

' BeginAdd
Dim value1 = 100.0R
Dim value2 = 15.99R

Dim arAdd As IAsyncResult = channelClient.BeginAdd(value1, value2, AddressOf AddCallback, channelClient)
Console.WriteLine("Add({0},{1})", value1, value2)

When the callback function executes, the client calls End<operation> (for example, EndAdd) to retrieve the result.

Example

The service that is used with the client code that is used in the preceding procedure implements the ICalculator interface as shown in the following code. On the service side, the Add and Subtract operations of the contract are invoked synchronously by the Windows Communication Foundation (WCF) run time, even though the preceding client steps are invoked asynchronously on the client. The Multiply and Divide operations are used to invoke the service asynchronously on the service side, even if the client invokes them synchronously. This example sets the AsyncPattern property to true. This property setting, in combination with the implementation of the .NET Framework asynchronous pattern, tells the runtime to invoke the operation asynchronously.

[ServiceContract(Namespace = "http://Microsoft.ServiceModel.Samples")]
public interface ICalculator
{
    [OperationContract]
    double Add(double n1, double n2);

    [OperationContract]
    double Subtract(double n1, double n2);

    //Multiply involves some file I/O so we'll make it Async.
    [OperationContract(AsyncPattern = true)]
    IAsyncResult BeginMultiply(double n1, double n2, AsyncCallback callback, object state);
    double EndMultiply(IAsyncResult ar);

    //Divide involves some file I/O so we'll make it Async.
    [OperationContract(AsyncPattern = true)]
    IAsyncResult BeginDivide(double n1, double n2, AsyncCallback callback, object state);
    double EndDivide(IAsyncResult ar);
}

<ServiceContract(Namespace:="http://Microsoft.ServiceModel.Samples")> _
Public Interface ICalculator
    <OperationContract> _
    Function Add(ByVal n1 As Double, ByVal n2 As Double) As Double

    <OperationContract> _
    Function Subtract(ByVal n1 As Double, ByVal n2 As Double) As Double

    'Multiply involves some file I/O so we'll make it Async.
    <OperationContract(AsyncPattern:=True)> _
    Function BeginMultiply(ByVal n1 As Double, ByVal n2 As Double, ByVal callback As AsyncCallback, ByVal state As Object) As IAsyncResult
    Function EndMultiply(ByVal ar As IAsyncResult) As Double

    'Divide involves some file I/O so we'll make it Async.
    <OperationContract(AsyncPattern:=True)> _
    Function BeginDivide(ByVal n1 As Double, ByVal n2 As Double, ByVal callback As AsyncCallback, ByVal state As Object) As IAsyncResult
    Function EndDivide(ByVal ar As IAsyncResult) As Double
End Interface

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How to: Call Operations Asynchronously Using a Channel Factory

Procedure

To call WCF service operations asynchronously

Example

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