title: Celery tasks pending while workers are available
body: <p>I have the following scenario:<br>
  I'm launching a first task (let's call it the parent task). This parent task then uses <code>group</code> to queue some children tasks. I need the return values of those children tasks and I would rather treat them as they come instead of waiting for all the children tasks to end, so I'm using a <code>join</code> on the result set returned by <code>group</code>, with the <code>callback</code> argument.  </p>
  
  <p>However, what happens is that, most of the time, a part of the children tasks stays in a pending state - while there are workers doing nothing - and the parent tasks runs forever. This seems to happen regardless of the number of workers.</p>
  
  <p>Am I misunderstanding something about Celery? I would think that this should not happen and available workers should start treating those tasks.<br>
  Or is it that the children tasks not run are queued to be run by the same worker running the parent task? In that case, what could I do?</p>