ASP.NET Life Cycle

The Two Step Process:

From 30,000 feet level ASP.NET request processing is a 2 step process as shown below.

Users Sends a requests to the IIS:-

 • ASP.NET creates an environment which can process the request. In other words it creates the application object, request, response and context objects to process the request.

 • Once the environment is created the request is processed through series of events which is processed by using modules, handlers and page objects. To keep it short lets name this step as MHPM (Module, handler, page and Module event), we will come to details later.

 

In the coming sections we will understand both these main steps in more details.

Creation of ASP.NET environment

Step 1:- The user sends a request to IIS. IIS first checks which ISAPI extension can serve this request. Depending on file extension the request is processed. For instance if the page is an ‘.ASPX page’ then it will be passed to ‘aspnet_isapi.dll’ for processing.

Step 2:- If this the first request to the website then a class called as ‘ApplicationManager’ creates an application domain where the website can run. As we all know application domain creates isolation between two web applications hosted on the same IIS. So in case there is issue in one app domain it does not affect the other app domain.

Step 3:- The newly created application domain creates hosting environment i.e. the ‘HttpRuntime’ object. Once the hosting environment is created necessary core  ASP.NET objects like ‘HttpContext’ , ‘HttpRequest’ and ‘HttpResponse’ objects are created.

Step 4:- Once all the core ASP.NET objects are created ‘HttpApplication’ object is created to serve the request. In case you have a ‘global.asax’ file in your system then object of the ‘global.asax’ file will be created.

Please note ‘global.asax’ file inherits from ‘HttpApplication’ class.

Note: The first time an ASP.NET page is attached to an application, a new instance of ‘HttpApplication’ is created. Said and done to maximize performance, ‘HttpApplication’ instances might be reused for multiple requests.

Step 5:- The ‘HttpApplication’ object is then assigned to the core ASP.NET objects to process the page.

Step 6:- ‘HttpApplication’ then starts processing the request by http module events , handlers and page events. It fires the MHPM event for request processing.

Note: - For more details http://msdn.microsoft.com/en-us/library/ms178473.aspx

Below image explains how the internal object model looks like for an ASP.NET request. At the top level is the ASP.NET runtime which has creates an ‘Appdomain’ which in turn has ‘HttpRuntime’ with ‘request’, ‘response’ and ‘context’ objects.

Process request using MHPM events fired :

Once ‘HttpApplication’ is created it starts processing request it goes through 3 different sections ‘HttpModule’ , ‘Page’ and ‘HttpHandler’. As it moves through these sections it invokes different events which the developer can extend and add customize logic to the same. Before we move ahead lets understand what are ‘HttpModule’ and ‘HttpHandlers’. They help us to inject custom logic before and after the ASP.NET page is processed.

The main differences between both of them are:-

• If you want to inject logic based in file extensions like ‘.ASPX’ , ‘.HTML’ then you use ‘HttpHandler’. In other words ‘HttpHandler’ is an extension based processor.

 

• If you want to inject logic in the events of ASP.NET pipleline then you use ‘HttpModule’. ASP.NET . In other word ‘HttpModule’ is an event based processor.

Below is the logical flow of how the request is processed. There are 4 important steps MHPM as explained below :-

 Step 1(M? Http Module):- Client request processing starts. Before the ASP.NET engine goes and creates the ASP.NET ‘HttpModule’ emits events which can be used to inject customized logic. There are 6 important events which you can utilize before your page object is created ‘BeginRequest’,’AuthenticateRequest’,’AuthorizeRequest’,’ResolveRequestCache’,’AcquireRequestState’ and ‘PreRequestHandlerExecute’.

Step 2 (H? ‘Http Handler’ ) :- Once the above 6 events are fired , ASP.NET engine will invoke ‘ProcessRequest’ event if you have implemented ‘HttpHandler’ in your project.

Step 3 (P – ASP.NET page):- Once the ‘HttpHandler’ logic executes the ASP.NET page object is created. While the ASP.NET page object is created many events are fired which can help us to write our custom logic inside those page events. There are 6 important events which provides us placeholder to write logic inside ASP.NET pages ‘Init’ , ‘Load’ , ‘validate’ , ‘event’ , ‘render’ and ‘unload’. You can remember the word ‘SILVER’ to remember the events S – Start ( does not signify anything as such just forms the word ) , I – (Init) , L ( Load) , V ( Validate) , E ( Event) and R ( Render).

Step4 (M? HttpModule):- Once the page object is executed and unloaded from memory ‘HttpModule’ provides post page execution events which can be used to inject custom post-processing logic. There are 4 important post-processing events ‘PostRequestHandlerExecute’, ‘ReleaserequestState’, ‘UpdateRequestCache’ and ‘EndRequest’.                   

Below figure shows the same in a pictorial format.