Asynchronous programming using IAsyncResult in ASP.NET

Here is the sample code for achieving asynchronous calls in ASP.NET using IAsyncResult

Asynchronous Provider:

public delegate List<Test> AsyncMethodCaller();
    public class AsyncProvider
    {
       
        public List<Test> GetTests()
        {
            System.Threading.Thread.Sleep(2000);
            return TestServices.provider.GetAllTests();
        }

    }

Using BeginInvoke and EndInvoke along with IAsyncResult in .aspx page:

public partial class TestAsync : System.Web.UI.Page
    {
        IAsyncResult result = default(IAsyncResult);
        AsyncProvider _provider = new AsyncProvider();
        AsyncMethodCaller caller = default(AsyncMethodCaller);
        List<Test> res = default(List<Test>);


        protected void Page_Load(object sender, EventArgs e)
        {
            txtFirstLoad.Text = "loaded first";           
        }
        protected override void OnInit(EventArgs e)
        {
            base.OnInit(e);
            caller = new AsyncMethodCaller(_provider.GetTests);
        }
        protected override void CreateChildControls()
        {
            base.CreateChildControls();
            result = caller.BeginInvoke(null, null);
        }
        protected override void OnPreRender(EventArgs e)
        {
            base.OnPreRender(e);
            res = caller.EndInvoke(result);
        }
        protected override void Render(HtmlTextWriter writer)
        {
            base.Render(writer);  
          
            grid.DataSource = res;
            grid.DataBind();
            grid.RenderControl(writer); 
        }
        public override void VerifyRenderingInServerForm(Control control)
        {
            return;
        }

    }