Are static class members pinned?

Question

I have a C# class, having a static ImageList object. This image list will be shared with various ListView headers (via SendMessage... HDM_SETIMAGELIST) on several forms in my application.

Though I understand that static objects are not eligible for garbage collection, it is not clear to me if they are also ineligible for relocation (compaction) by the garbage collector. Do I also need to pin this object since it is shared with unmanaged code, say, using GCHandle.Alloc?

Environment is VS 2008, Compact Framework 3.5.

Answer 1

The instance itself is not static. The reference is. If you null the reference the instance becomes eligible for GC. Internally, all static instances are references through a pinned handle to an array of statics. I.e. the instance is implicitly pinned by the runtime.

If you look at the GCroot of an instance declared as a static member, you'll see something like this:

HandleTable:
    008113ec (pinned handle)
    -> 032434c8 System.Object[]
    -> 022427b0 System.Collections.Generic.List`1[[System.String, mscorlib]]

If you null the static reference the corresponding entry in the pinned array is nulled as well.

Now, these are obviously implementation details so they could potentially change.