MSDN tells me that handles to windows (HWND) can be shared between 32- and 64-bit applications, in Interprocess Communication (MSDN). However, in Win32 a HWND is 32 bits, whereas in 64 bit Windows it is 64 bits. So how can the handles be shared?
I guess the same question applies to handles to named objects such as mutexes, semaphores and file handles.
Doesn't the fact that they can be shared imply that only the lower 32 bits are used in Win64 processes? Windows handles are indexes not pointers, at least as far as I can tell, so unless MS wanted to allow more than 2^32 window/file/mutex/etc. handles there's no reason to use the high 32 bits of a void* on Win64.