I'm working on an update to threads::shared right now. There will be only minor changes: An update to ppport.h and improvements in the docs (notably information regarding the use of bless with shared variables). I'll add an exported function called 'is_shared' that will be an alias to '_id'. That should make it formal enough.

I, too, used '_id' to test for sharing in the Object::InsideOut module, so I see this as a good addition to the module.

Update: Uploaded to CPAN on 2006-02-27.