If your ok with stopping the world every once in a while I don't think recounting needs to be globally synchronized. You just stop the world, do the recount fro

If your ok with stopping the world every once in a while I don't think recounting needs to be globally synchronized. You just stop the world, do the recount from an append only thread safe log, and start the world again. No synchronization needed. What you (arguably) save is a scan of all pointers to see if they point to your object.