What is the difference between managed and native resources when disposing? (.NET)

Question

I was reading the MSDN article about how to implement IDisposable and I am uncertain about the difference between managed and native resources cited in the article.

Answer 1

The short answer would be anything that you go behind the CLR's back (to the OS) to obtain can be termed as 'native'.

• unmanaged memory allocation. If you 'new' up a chunk of memory in a managed class CantStayManaged, then CantStayManaged is responsible for freeing this memory (resource).
• handles to files, pipes, events, synchronization constructs, etc. - as a thumb rule if you call WinAPIs to obtain pointers/handles to a resource, then those are 'native resources'

So now CantStayManaged has 2 things it needs to cleanup before it bids adieu.

1. Managed: Member fields and any resources the CLR allocated. This usually equates to calling Dispose on your 'Disposable' member objects.
2. Unmanaged: all the sneaky low-level stuff we pull behind its back.

There are 2 ways the object cleanup can be triggered now.

1. Dispose(true) case: You called Dispose explicitly on your type. Good programmer.
2. Dispose(false) case: You forgot to call Dispose, in which case the finalizer should kick in and still ensure proper cleanup.

In both cases, the unmanaged resources should be freed up else 'LEAKS!', 'CRASHES!' et.all surface. But you should only attempt to cleanup managed resources only in Dispose() former case. In the latter/finalizer case - the CLR might have already finalized and collected some of your members, so you shouldn't access them (CLR doesn't guarantee an order in which an object graph is finalized.) Hence you avoid issues by guarding your managed cleanup with an if (AmIBeingCalledFromDispose) guard check

HTH