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Asynchronous Execution in ASP.NET



Asynchronous Execution:
Two ways either implement IHTTPAsyncHandler interface or in ASP.NET 2.0 set
<%@ Page Async=”true” %>.

The second option implements IHTTPAsyncHandler interface automatically for the page when parsed or compiled.

AddOnPreRenderCompleteAsync (
new BeginEventHandler(BeginTask),
new EndEventHandler(EndTask));

AddOnPreRenderCompleteAsync() shoud be called in Page_load. The BeginEventHandler and EndEventHandler are delegates defined as follows:

IAsyncResult BeginEventHandler(
object sender,
EventArgs e,
AsyncCallback cb,
object state)

void EndEventHandler(
IAsyncResult ar)

AsyncProcess starts and completes between PreRender and PreRenderComplete.

Other way to perform Async Task is using AsyncPageTask structure. It also allows multiple tasks to execute simultaneously.

void Page_Load (object sender, EventArgs e)
{
PageAsyncTask task = new PageAsyncTask(

new BeginEventHandler(BeginTask),
new EndEventHandler(EndTask),

null,    //Time out event handler (optional)
null,    //State – e.g Name “Thread 1” or any data
0);      // Run Simultaneously Boolean

RegisterAsyncTask(task);
}

By default timeout is 45 Seconds and can be modified in Web Config:
<system.web>
<pages asyncTimeout=”30” />
</system.web>

Or

<%@ Page AsyncTimeout=”30” %> directive.

To even improve performance and take out the advantage one can start PageAsyncTasks at any time after registering by Calling Page.ExecuteRegisteredAsyncTasks().

Page LifeCycle:
PreInit(2.0)            Posted Data is available
Init                        (ViewState No Available, Personalization info is setup)

àViewState Tracked Here

InitComplete(2.0)   Complete View State Available

à Override protected virtual LoadViewState on user custom controls to load your view state persisted previously.

PreLoad(2.0)          Only for Pages
Load                      Safe to work here

à Dynamically Created controls in load are given a try to match the posted data and update their information after Load event.

LoadComplete(2.0) Page preparation and initialization phase completed. It’s just a signal. After this Page will enter into rendering phase.

PreRender
PreRenderComplete (2.0) Only for Page.

SaveStateComplete (2.0) Saves controls state into __ViewState hidden field.

          SavePageStateFromStorageMedium and LoadPageStateFromStorageMedium can be used to store info in any other medium.
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