Question

I have an unmanged class and a ref class which ar logically connected:

public ref class RefBlah
{
   ~RefBlah();
   !RefBlah();

   internal:

   UnManagedBlah* m_unmanaged;
}

public class UnManagedBlah
{
    public:
    gcroot<RefBlah^> refBlah;
}

The RefBlah class always creates an instance of UnManagedBlah which holds a reference to the object that created it.

Now, when I create an instance of RefBlah in a C# application, it just doesn’t get freed when it get out of scope. (I’ve waited and seen all the other objects get freed, but it refuses to remove itself).

As far as I know, if they were both regular .Net objects, they would both be collected when the class gets out of scope because although the reference count does not reach 0. And that’s because there’s no refernce root to the objects from the main stack.

Does .NET GC treat references from unmanaged classes differently ?

How can I change the design so that RefBlah will be destroyed ?

Answer 1

I think you have a circular reference problem. RefBlah won’t get GC’d until the reference in UnManagedBlah is GC’d which will only happen when you delete the pointer in RefBlah etc..

If you need to have a reference inside the unmanaged class then perhaps it should be a weak reference? Have a look at the GCHandle struct:

The GCHandle class is used with the
GCHandleType enumeration to create a
handle corresponding to any managed
object. This handle can be one of four
types: Weak, WeakTrackResurrection,
Normal, or Pinned. When the handle has
been allocated, you can use it to
prevent the managed object from being
collected by the garbage collector
when an unmanaged client holds the
only reference. Without such a handle,
the object can be collected by the
garbage collector before completing
its work on behalf of the unmanaged
client.