class="identifier">clear_queue</span><span class="special">()</span></code> is called, <code class="computeroutput"><span class="identifier">buf_id_check</span></code>
                  increments the buffer id. When an iterator is dereferenced, this
                  policy checks that the buffer id of the iterator matches the shared
                  buffer id. This policy is most effective when used together with
                  the <code class="computeroutput"><span class="identifier">split_std_deque<