Question about the use and scope of global.asax (for file cleanup after application ends)

Question

Hey guys, I apologize for this basic question, but for the life of me I can't seem to find an answer.

I previously asked a question here about how to dynamically store temporary images and handle their cleanup on a web server's file system. (using C# in .NET 3.5)

It was suggested that I use a global.asax file to handle this.

I just can't figure out how this thing works.

I have two separate applications... So far, I have figured out that the global.asax is supposed to be in the root directory of the website.

Questions:

1) How to I get the global.asax to fire for only these two specific applications.

2) both applications need to create a list of strings (the file locations) then delete them on the application termination. Do I instantiate this array in the app, or in the global.asax?

my code will look like this

List<string> fileLocations = new List<string>();  //I don't know where to put this.

//The next line of code will be in both applications (this could be called many times in one application session.  The names of the files are generated from the clock (milliseconds and seconds combined, I might change this to use the actual random class combined with sessionID)
fileLocations.Add(file);

void Application_End(object sender, EventArgs e) 
{
    //  Code that runs on application shutdown
    foreach(string file in fileLocations)
    {
        if(File.Exists(file))
            File.Delete(file);
    }    
}

I am confused about how the global.asax actually works. Is it used like an interface?

Answer 1

MSDN Link and Wikipedia Link are places to start.

It isn't used like an interface, more like a filter that has a bunch of different hooks for things like starting the Application object or a Session or a Request. The Wikipedia link has a list of calls that the Global.asax can make though I would suggest stepping back for a moment to understand how a web application ends compared to a desktop application. IIS can recycle an AppPool as one way to end the application though there are others so setting a cleanup on application end may not be the best idea if that event never fires.

Answer 2

A good place to look at how to use Global.asax is to read the ASP.NET Quickstart on it's usage. You have one per web application / site. It's kind of like Global level events.

Be aware, the Application_End event will not fire often, on most servers. It will only fire if the IIS app pool is unloaded/recyclyed, web.config modified , assemblies changed in /Bin,or someother situation where the webserver stops. On a popular site it could be weeks, months before your event ever fires.