behavior she can do so by
  instantiating <code>fifo_scheduler&lt;&gt;</code> with her own class
  modeling the <code>FifoWorker</code> concept. I considered a much more
  generic design where locking and waiting is implemented in a policy but I
  have so far failed to come up with a clean and simple interface for it.
  Especially the waiting is a bit difficult to model as some platforms have
  condition variables, others have events and yet others don't have any
  notion of waiting whatsoever (they instead