question on nsIWeakReference

[jml]

I have some question on nsIWeakReference and nsISupportsWeakReference.

1. How error code should nsIWeakReference.queryReferent() return if the corresponding xpcom object is disposed?

2. For the whole design, why require the nsISupportsWeakReference interface? I don't see the necessary of the nsISupportsWeakReference interface, at least, if one can provide an nsIWeakReference, why care about nsISupportsWeakReference?

3. BTW, it is very easy to implement the nsIWeakReference in java, only need to use the java weakreference support. Can anyone explain how weakreference works in the C/C++ world? I noticed there are a lot of C/C++ macro for it, hard to understand for me :-)

Thanks

jml