But if you have both atomic primitives available, why would you ever do that? Keyword is atomic. Fetch-and-add returns you the previous value atomically. ----

But if you have both atomic primitives available, why would you ever do that? Keyword is atomic. Fetch-and-add returns you the previous value atomically. ------- Edit: This (below) is obviously a buggy reference counting algorithm. ------- In freeing (decrementing reference count) thread A, if it was 1 before (returned value) and A added -1, the object can be freed. Because the operation is atomic, only one of two things can happen: 1) Another reference adding thread B increments it before A decreases it. So A doesn't see 1, thus won't free the object. 2) B increments it after A decremented it. So B gets zero and knows the object is invalid. (Edit: Oops, a bug: after B increments refcount, when thread C tries to do same, it would get 1 and conclude the object is valid!) If B is allowed to allocate the object again (invalid state, refcount == 0), careful synchronization needs to be done remove any races with A's deallocation.