Questions regarding freeing resources reserved by MarshalInterface.FromManaged()

[mqudsi]

Hello team,

I'm making the transition from the old Framework-provided CCW marshalling to the new CsWinRt/WASDK-provided alternative and there's something I'm not clear about.

The old Marshal.GetComInterfaceForObject() approach was well-documented and made it clear that pinned memory and resources for the CCW are reserved until a paired call to Marshal.Release() was made to decrement the internal ref count and trigger the release of associated resources.

I can't for the life of me find any documentation on the new MarshalInterface<T> and co. but just going by the code, MarshalInterface<TInterface>.FromManaged(new T()) returns a bare pointer (well, IntPtr) but it seems that lifetime tracking is provided by the ObjectReference<TInterface> class; all of which would imply that a bare IntPtr returned from MarshalInterface.FromManaged() doesn't have any sort of reference counting, which leads to some questions:

I'm assuming the IntPtr returned from MarshalInterface.FromManaged() is obviously pinned, or else it would be unsafe to directly use/return as a CCW. How is that memory unpinned and the CCW destroyed? Is that the job of MarshalInterface.DisposeAbi() (which seems like it's the counterpart to MarshalInterface.FromAbi() and not MarshalInterface.FromManaged())?

The interop docs say the new replacement for Marshal.Release() is only via the ObjectInterface class - does that mean that we actually can't use the IntPtr returned by MI.FromManaged() without first using ObjectReference.Attach() and then using IObjectReference.GetRef() to get the CCW? I'm guessing no because it would've made more sense to have MI.FromManaged() return an IObjectReference directly instead of an IntPtr in that case?

Basically, what do I have to do after using MarshalInterface<TInterface>.FromManaged(new T()) in my IClassFactory/COM server to make sure nothing is leaked?

[manodasanW]

@mqudsi When you call FromManaged on a C# implemented object, a CCW is created for it (if none exists) for which the pointer is returned and the reference count on the CCW is incremented. This pointer which is returned is basically the ABI representation of the object and also owns the reference count. If you want to release the reference, you can make use of DisposeAbi as you mentioned or if you passed that pointer to the native side, the native side can call Release on the IUnknown interface just like any other COM object.