maybe_like_this.erl

+wait_loop(Parent, Timeout, State) ->
    % State transitions
    % unset -> (updated | timeout | waiting)
    % updated -> (updated | unset)
    % timeout -> (unset | updated)
    % waiting -> unset
    receive
        db_updated when State == waiting ->
            Parent ! updated,
            wait_loop(Parent, Timeout, unset);
        db_updated when State == unset orelse State == updated ->
            wait_loop(Parent, Timeout, updated);
        get_state when State == unset ->
            wait_loop(Parent, Timeout, waiting);
        get_state ->
            Parent ! State,
            wait_loop(Parent, Timeout, unset);
        done ->
            ok
    after Timeout ->
        case State of
            waiting ->
                Parent ! timeout;
            unset ->
                wait_loop(Parent, Timeout, timeout)
        end
     end.

Agree about the timeout (typo there), not sure I agree about the drain but I'll defer to your judgement there. Let me push a PR so we can get more eyeballs on it

cloudant/fabric@cca4750