// If the content is not shared, or if it is shared and the reference
// count has dropped to zero, deallocate it.
if (!(u.lmsg.flags & msg_t::shared) ||
!u.lmsg.content->refcnt.sub (1)) {
// We used "placement new" operator to initialize the reference
// counter so we call the destructor explicitly now.
u.lmsg.content->refcnt.~atomic_counter_t ();