code: func (q *DurableQueue) SetDest(dest string) string {
  	q.dmu.Lock()
  	defer q.dmu.Unlock()
  
  	q.dest = dest
  
  	return q.dest
  }
docs: // SetDest updates the destination where items are "pulled" to in a safe,
  // blocking manner. It does this by first obtaining a write-level lock on the
  // internal member variable wherein the destination is stored, updating, and
  // then relinquishing the lock.
  //
  // It returns the new destination that was just set.