Question

I have a number of classes which have private member variables that implement IDisposable (timers, brushes, etc). Do I need to do anything to ensure these variables are cleaned up properly by the .NET Framework?

The literature I’ve come across is referring to “managed resources” vs. “unmanaged resources”. These terms are confusing to me because you can have a managed class which implements functionality using unmanaged resources. Is that considered an “unmanaged resource” or “managed resource” ?

My understanding is if you aren’t calling Dispose() on an object that implements IDisposable, then the resources aren’t being freed until the application exits. This situation could cause OutOfMemory exceptions when running the program for a long period of time.

How can I be sure my code is handling resource management correctly? It’s important for these objects because they are custom controls and there may be a lot of drawing which consumes IDisposable resources. I use the C# using statement whenever I can, but sometimes I need to make an object implementing IDisposable a member variable, and the using statement won’t help me there.

Answer 1

Three simple rules.

A managed resource is anything implementing IDisposable. An unmanaged resource is something like a HANDLE that you got via p/Invoke. A class like SafeHandle (or one derived from SafeHandle) owns an unmanaged resource, but it is considered a managed resource itself. So any class that owns unmanaged resource is itself a managed resource.

Since you have a class owning managed resources, follow Rule 2: implement IDisposable (but not a finalizer).

IDisposable allows for earlier cleanup. If you don’t call it, the resources will be cleaned up anyway (they won’t hang around until process exit); they’ll just be cleaned up later, and you don’t have a choice about when they get cleaned up.