in C++, what do the underscore signs in the multi-inheritance classes mean?
<p>here is the code:</p>

<pre><code>PiGenerator::PiGenerator(PP_Instance instance)
: pp::Instance(instance),
  graphics_2d_context_(NULL),
  pixel_buffer_(NULL),
  flush_pending_(false),
  quit_(false),
  compute_pi_thread_(0),
  pi_(0.0) {
  pthread_mutex_init(&amp;pixel_buffer_mutex_, NULL);
}
</code></pre>

<p>Or is this even multi-inheritance? Can someone enlighten me?</p>
