At today's .NET user group meeting someone asked about doing async tasks in an ASP.NET page and not blocking. Here is one option in all it's g(l)ory:

The ASPX @page directive gains a AsyncTimeOut="3" which will make it wait up to 3 seconds for the async task to complete. Since the operation itself does not actually use an external resource, a fake out of the AsyncResult is done using a delegate and a BeginInvoke on it which yields the IAsyncResult that BeginEventHandler is expected to return and EndEventHandler requires. If the work was actually a http web request or something, it would have a BeginInvoke provided by the proxy.

The code in front:

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<%@ Page Language="C#" 
AutoEventWireup="true"  
CodeFile="Default.aspx.cs" 
Inherits="_Default" 
Async="true"
AsyncTimeOut="3"
%>

<!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>Async processing</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
    <asp:Literal runat="server" ID="Output"></asp:Literal>
    </div>
    </form>
</body>
</html>

==============================

and the code behind:

==============================

 

using System;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class _Default : System.Web.UI.Page 
{
    protected delegate void DoTheWorkDelegate();
    private DoTheWorkDelegate _doTheWorkDelegate;
    private TimeSpan _workTime = TimeSpan.FromSeconds(2);

    private string _report = ">";

    public string Report
    {
        get { return _report; }
        set { _report += value + "... "; }
    }


    protected void Page_Load(object sender, EventArgs e)
    {
        if (! String.IsNullOrEmpty( Request.QueryString["t"]))
        {
            _workTime = TimeSpan.FromSeconds(double.Parse(Request.QueryString["t"]));
        }

        PageAsyncTask task = new PageAsyncTask(
            new BeginEventHandler(BeginAsyncOp),
            new EndEventHandler(EndAsyncOp),
            new EndEventHandler(TimedOutOp),
            null);

        RegisterAsyncTask(task);
        Report = "page load completed";
    }

    protected override void Render(HtmlTextWriter wr)
    {
        Output.Text = Report;
        base.Render(wr);
    }

    IAsyncResult BeginAsyncOp(object sender, EventArgs e, AsyncCallback cb, object state)
    {
        this.Report = "Begin Async";
        _doTheWorkDelegate = new DoTheWorkDelegate(doTheWork);
        return _doTheWorkDelegate.BeginInvoke(cb,state);
    }

    void EndAsyncOp(IAsyncResult ar)
    {
       Report = "End Async";
    }

    void TimedOutOp(IAsyncResult ar)
    {
        Report = "Timed Out";
    }

    void doTheWork()
    {
        System.Threading.Thread.Sleep(_workTime);
    }
}