e B holds a borrowed handle X (to an A-allocated object). Now A dtor runs; its <code>.session_shm()</code> arena &ndash; its constitutent SHM-pools! &ndash; is destroyed. That in itself shouldn't be a problem; again B presumably holds a SHM-pool handle, so it won't just disappear from RAM under it. I (ygoldfel) am somewhat fuzzy on what exactly happens (not being the direct author of SHM-jemalloc), but basically as I understand it, in destroying the arena, a bunch of jemalloc deinit steps execute; perhaps h