Dispose question

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

Very comprehensive IDisposable guidelines are here.

Do transitively dispose of any disposable fields defined in your type from your Dispose method.

You should call Dispose() on any fields whose lifecycle your object controls. For example, consider a case where your object owns a private TextReader field. In your type's Dispose, you should call the TextReader object's Dispose, which will in turn dispose of its disposable fields (Stream and Encoding, for example), and so on. If implemented inside a Dispose(bool disposing) method, this should only occur if the disposing parameter is true—touching other managed objects is not allowed during finalization. Additionally, if your object doesn’t own a given disposable object, it should not attempt to dispose of it, as other code could still rely on it being active. Both of these could lead to subtle-to-detect bugs.

Do implement the dispose pattern when your type is unsealed and contains resources that explicitly need to be or can be freed, for example raw handles, or other unmanaged resources.

This pattern provides a standardized means for developers to deterministically destroy or free resources owned by an object. It also aids subclasses to correctly release base class resources.

'Unmanaged resource' usually refers to cases where your code refernces native handles directly (file handles, connections, sockets etc). In this case you would also have to implement finalizer or use SafeHandle. Most of the time you reference native handles indirectly, through .NET classes like TextReader. In this case you can simply use 'using' or, if you are writing library, implement IDisposable transitively.