如何设置IHttpAsyncHandler

我正在尝试设置一个异步HttpHandler，但我不知道我是否走在了正确的轨道上。似乎没有太多的文档。我只想得到启动DoWork（）方法async的请求。

有几件事我不确定：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.IO;
using System.Text;

public class WebServiceHandlerAsync : IHttpAsyncHandler
{
    /// <summary>
    /// BeingProcessRequest
    /// </summary>
    public IAsyncResult BeginProcessRequest(HttpContext context, AsyncCallback cb, object extraData)
    {
        context.Response.Output.WriteLine("Starting");
        context.Response.Flush();
        // Invokes the BeginProcessRequest method on the asynchronous HTTP handler
        RequestResult result = new RequestResult(context, null, extraData);
        result.DoWork();
        return result;
    }
    /// <summary>
    /// Do on end of request (blocking)
    /// </summary>
    public void EndProcessRequest(IAsyncResult result)
    {
    }

    public bool IsReusable
    {
        get { return true; }
    }

    public void ProcessRequest(HttpContext context)
    {
        throw new NotImplementedException();
    }
}


/// <summary>
/// Async object
/// </summary>
public class RequestResult : IAsyncResult
{
    public HttpContext Context { get; private set; }
    private bool _completed;
    private object _extraData;
    public object AsyncState
    {
        get { return _extraData; }
    }
    public System.Threading.WaitHandle AsyncWaitHandle
    {
        get { throw new NotImplementedException(); }
    }
    public bool CompletedSynchronously
    {
        get { return false; }
    }
    public bool IsCompleted
    {
        get { return _completed; }
    }

    /// <summary>
    /// Constructor
    /// </summary>
    public RequestResult(HttpContext context, AsyncCallback callback, object extraData)
    {
        Context = context;
        _extraData = extraData; 
    }

    /// <summary>
    /// Handle request
    /// </summary>
    public void DoWork()
    {    
        // do some work
        Context.Response.Output.WriteLine("Working...");
        _completed = true;
    }
}