code: func (p *PriorityQueue) AddIfNotPresent(pod *v1.Pod) error {
  	p.lock.Lock()
  	defer p.lock.Unlock()
  	if p.unschedulableQ.get(pod) != nil {
  		return nil
  	}
  
  	pInfo := p.newPodInfo(pod)
  	if _, exists, _ := p.activeQ.Get(pInfo); exists {
  		return nil
  	}
  	if _, exists, _ := p.podBackoffQ.Get(pInfo); exists {
  		return nil
  	}
  	err := p.activeQ.Add(pInfo)
  	if err != nil {
  		klog.Errorf("Error adding pod %v/%v to the scheduling queue: %v", pod.Namespace, pod.Name, err)
  	} else {
  		p.nominatedPods.add(pod, "")
  		p.cond.Broadcast()
  	}
  	return err
  }
docs: // AddIfNotPresent adds a pod to the active queue if it is not present in any of
  // the queues. If it is present in any, it doesn't do any thing.