pan class="identifier">sinks</span><span class="special">::</span><span class="identifier">unbounded_ordering_queue</span><span class="special">&lt;</span>                                             <a class="co" name="log.detailed.sink_frontends.async.c6" href="sink_frontends.html#log.detailed.sink_frontends.async.c7"><img src="../../../../../../doc/src/images/callouts/1.png" alt="1" border="0"></a>
        <span class="identifier">logging</span><span class="special">::</span><span class="identifier">attr