Calling WCF service asynchronously from ASP.NET
I was recently asked how to call WCF Service asynchronously from ASP.NET. Here's my sample code:
1) WCF Service Library Implementation
namespace WcfServiceLibrary1
{
[ServiceContract]
public interface ISampleService
{
[OperationContract]
string SayHelloWorld();
}
}
namespace WcfServiceLibrary1
{
public class Service1 : ISampleService
{
#region ISampleService Members
public string SayHelloWorld()
{
//Simulate it running longer than it usually takes for the page to handle request
System.Threading.Thread.Sleep(5000);
return "Hello World";
}
#endregion
}
} 2) ASP.NET side using the service
<%@ Page Async="true" Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:Button ID="Button1" runat="server" Text="Call the service"
onclick="Button1_Click" />
<asp:Label ID="Label1" runat="server" ></asp:Label>
</div>
</form>
</body>
</html>
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
public partial class _Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
}
ServiceReference1.SampleServiceClient client = null;
protected void Button1_Click(object sender, EventArgs e)
{
PageAsyncTask task = new PageAsyncTask(BeginGetAsyncData, EndGetAsyncData, null, null);
Page.RegisterAsyncTask(task);
}
IAsyncResult BeginGetAsyncData(object src, EventArgs args, AsyncCallback cb, object state)
{
client = new ServiceReference1.SampleServiceClient();
return client.BeginSayHelloWorld(cb, state);
}
void EndGetAsyncData(IAsyncResult ar)
{
string returnedValue = client.EndSayHelloWorld(ar);
Label1.Text = DateTime.Now.ToString() + ":" + returnedValue;
}
}
Points to get:
- Async="True" in @page directive
- Use of PageAsyncTask to register the task (steps when starting the async action, and steps to end it) , supports tasks running parallel
- Using Begin/End methods of the WCF service (Begin/EndSayHelloWorld instead of SayHelloWorldAsync e.g not using event based implementation because ASP.NET already provides hooks to the async pattern)
- these async tasks execute between PreRender and PreRenderComplete - they're done when PreRenderComplete executes (page waits for them to execute, releasing the worker thread to the pool, and then spins up another one to end the request when async tasks are done) - e.g from user perspective it might not seem so fancy although if you can run tasks parallel, user sees it as better performance since page responds faster
Resources about async pages/ calling WCF
http://weblogs.asp.net/despos/archive/2005/10/19/427861.aspx
http://msdn.microsoft.com/en-us/library/ms734701.aspx