.Net Core execution flow - ProcessRequestNotification & FinishPipelineRequest getting called Four times per request.

Hi ,

This topic is in depth regarding architectural functionality of ASP.NET . 

I am having a small ASP.NET web application that displays a chart when it is loaded. I do helper function call injection in all the .Net functions that are coming to JITCompilation, So that all the .NET functions will call my helper functions when it is being called. Inside the helper function i log the function names. 

I am getting some strange observations when looking into the log file. 

For each request that is getting triggered , I am getting four "Hosting.PipelineRuntime:ProcessRequestNotification" and "HttpRuntime:FinishPipelineRequest" . When getting the URL inside those functions i am getting as follows. 

http://localhost:999/SaveToImage.aspx , http://localhost:999/ , http://localhost:999/ , http://localhost:999/ChartImg.axd?i=charts_0/chart_0_0.png&g=d8389079da824024a9ed19217e124715

And i also found that those four function calls have different HttpContext.Current object .  And the thread ID is same for 1st three function Calls and different for last function alone. 

Can any one explain me why this works like this.? This goes to the interior of .NET stuff. I am very much blank on this topic. 

Thanks,

./Selva