code: func (q *TransferQueue) Watch() chan *Transfer {
  	c := make(chan *Transfer, q.batchSize)
  	q.watchers = append(q.watchers, c)
  	return c
  }
docs: // Watch returns a channel where the queue will write the value of each transfer
  // as it completes. If multiple transfers exist with the same OID, they will all
  // be recorded here, even though only one actual transfer took place. The
  // channel will be closed when the queue finishes processing.