The idea of Asynchronous Pages is to free IIS so more users can be served, if you create a page that "never" finishes, you will eat up all your resources.
That been said... if you still want to do it...
We "know" (documentation), Asynchronous Pages work by splitting the execution of the page in 2... everything BEFORE the Background Tasks and everything AFTER the tasks, in that way IIS can process more requests while the background tasks finish their work. (there is more to it, but that is enough for now)
So... they "must" be creating some kind of Task Manager (like a root/main task) that executes all the registered tasks in sequence, in that way IIS starts processing the page, fires up the task manager, frees IIS, the task manager keeps processing the tasks and when it finishes, it returns control to IIS.
That would explain why the AsyncTimeout controls all the registered tasks instead of one-by-one (The timeout is actually applied to the Task Manager).
I tested a variation of your code with a timeout of 6000 seconds and it works:
C#:
protected void Page_Load(object sender, EventArgs e)
{
Page.RegisterAsyncTask(new PageAsyncTask(ProcessTask));
}
protected async Task ProcessTask()
{
await Task.Delay(1000);
Response.Write(DateTime.Now.ToLongTimeString() + "<br/>");
Response.Flush();
Page.RegisterAsyncTask(new PageAsyncTask(ProcessTask));
}
aspx:
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="Sample03.Default" Async="true" AsyncTimeout="6000" %>
Hope it helps.