ver know if the task has been performed
      correctly, since there is no response from the worker.
      This is one of the reasons that the pipeline pattern 
      should usually not be used alone, but in the context of
      a balancer. (You usually want to push 
      a request to a worker through a balancer --
      one of the ideas behind pusher/woker is work balancing.)
      A balancer may request providers to send <em>heartbeats</em>
      and, this way, minimise the risk of failure.
      The wor