How to Delete Entries In Static Dictionary When Not Used

Question

I have a static class that holds a dictionary of objects. I have multiple threads that access this dictionary and create objects on it that are specific to that thread. How and when can I remove entries from the dictionary when a thread is "done"?

Basically this is a static class for an ASP.NET application that all requests can have "isolated objects" (that are related to the current thread) created in the dictionary. But, I don't really want to be tied to ASP.NET.

Does this make sense?

Answer 1

You can decorate a static field with a [ThreadStatic] attribute and each thread will see its own value. If you are using .NET 4.0, you can use ThreadLocal<T> to do that too. Basically, you'd have a separate dictionary for each thread holding its own objects rather than saving all objects in a single dictionary.

Answer 2

Assuming that you store the id of the thread (or some other unique identifier) with the objects you could fire an event from the thread closing code - with this unique id - to let the dictionary know that the thread has finished with it's objects.

Your static class could subscribe to this event and then loop through the dictionary removing all objects that have this id.

I think.

Answer 3

It sounds like your dictionary is being used as a cache.

Have you considered using an existing caching solution instead of rolling your own? The Enterprise Library has a nice caching block that allows you an enormous amount of flexibility in how you manage the lifecycle of the objects you cache, including timing them out after a period of inactivity. (i.e. thread has disappeared)