A, and is later done with it &ndash; the <code>shared_ptr</code> local ref-count reached 0 &ndash; SHM-jemalloc-arranged <code>shared_ptr</code> deleter will send an internal message over a special channel to A. A will deallocate X once that has occurred, <em>and</em> any A-held <code>shared_ptr</code> group for X has also reached ref-count 0 (which may have happened before, or it may happen later). Exactly the same is true of A borrowing from B, conversely/symmetrically.</p>
<p >The problem is this: Suppos