ifo_scheduler&lt;&gt;</code> can only host
  <code>event_processor&lt;&gt;</code> subtype objects;
  <code>asynchronous_state_machine&lt;&gt;</code> is just one way to
  implement such a processor). Moreover,
  <code>create_processor&lt;&gt;()</code> only returns a
  <code>processor_handle</code> object. This must henceforth be used to
  initiate, queue events for, terminate and destroy the state machine through
  the scheduler.</p>

  <h3>Customization</h3>

  <p>If a user needs to customize the scheduler 