Are static class instances unique to a request or a server in ASP.NET?

Solution 1:

Your static classes and static instance fields are shared between all requests to the application, and has the same lifetime as the application domain. Therefore, you should be careful when using static instances, since you might have synchronization issues and the like. Also bear in mind, that static instances will not be GC'ed before the application pool is recycled, and therefore everything that is referenced by the static instance, will not be GC'ed. This can lead to memory usage problems.

If you need an instance with the same lifetime as a request, I would suggest to use the HttpContext.Current.Items collection. This is by design meant to be a place to store stuff that you need througout the request. For nicer design and readability, you can use the Singleton pattern to help you manage these items. Simply create a Singleton class that stores its instance in HttpContext.Current.Items. (In my common library for ASP.NET, I have a generic SingletonRequest class for this purpose).

Solution 2:

Static members have a scope of the current worker process only, so it has nothing to do with requests, because different requests may or may not be handled by the same worker process.

• In order to share data with a specific user and across requests, use HttpContext.Current.Session.
• In order to share data within a specific request, use HttpContext.Current.Items.
• In order to share data across the entire application, either write a mechanism for that, or configure IIS to work with a single process and write a singleton / use Application.

By the way, the default number of worker processes is 1, so this is why the web is full of people thinking that static members have a scope of the entire application.

Solution 3:

Since the types are contained in an app domain, I would expect static classes to be present as long as the app domain is not recycled, or if the request gets served by a different app domain.

I can think of several ways to make objects specific to a particular request depends on what you want to do, for e.g. you could instantiate the object in Application.BeginRequest and then store it in HttpRequest object so that it can be accessed by all objects in the request processing pipeline.

Solution 4:

If they are not unique to each request, is there a way to allow them to be?

Nope. Static members are owned by the ASP.NET process and shared by all users of the Web app. You'll need to turn to other session management techniques such as session variables.