title: TPL Dataflow block with an inner life
body: <p>I've been doing a bit of TPL dataflow coding and am quite happy with the basics. The question I have is, how would I go about doing a TPL block that, besides reacting to its queue, also has a life on its own?</p>
  <p>Like, a background task that runs on a permanent loop, polling the odd webservice or database every few seconds and emitting messages on its outputs when it sees fit?</p>
  <p>The interface would be a source- and target block, but with no apparent connection between source messages and target messages.</p>
  <p>Basically an &quot;active&quot; block.</p>