code: def _init_queue():
          
          LOG.info('Initialising Processing Block queue.')
          queue = ProcessingBlockQueue()
          active_pb_ids = ProcessingBlockList().active
          LOG.info('Initialising PC PB queue: %s', active_pb_ids)
          for pb_id in active_pb_ids:
              pb = ProcessingBlock(pb_id)
              queue.put(pb.id, pb.priority, pb.type)
          return queue
docs: Initialise the Processing Block queue from the database.
  
          This method should populate the queue from the current state of the
          Configuration Database.
  
          This needs to be based on the current set of Processing Blocks in
          the database and consider events on these processing blocks.