it uses to communicate with the borrower process: the arena is told there's nothing out there pointing into it: locally the user has to have dropped all constructed-object handles; and the borrower process it no longer has a way of contacting it; so it assumes tgat guy's done/gone, as are all the borrowed handles in it. That clarification doesn't change the situation though: Whether it's the SHM-jemalloc-session, or the SHM-jemalloc-session-used-channel, or the SHM-jemalloc-arena going away that makes borro