mputeroutput">last_value</code>
      combiner used by default in the original Boost.Signals library.
      This is because <code class="computeroutput">last_value</code> requires that at least 1 slot be
      connected to the signal when it is invoked (except for the <code class="computeroutput">last_value&lt;void&gt;</code> specialization).
      In a multi-threaded environment where signal invocations and slot connections
      and disconnections may be happening concurrently, it is difficult
      to fu