avoid sharedIndexInformer run more than once, avoid more cache and me…

[kitianFresh]

What type of PR is this?

/kind feature

What this PR does / why we need it:

avoid the informer to be run more than once by return explict error or by some check

Which issue(s) this PR fixes:

following code has some bug, because the nodeInformer will start more than once, then there will be two reflectors, two DeltaFIFOs, and two goroutines to list watch nodes data, and it can run normally but it will consume more resources.

we should avoid the informer to be run more than once by return explict error or by some check

	podInformer := NewPodInformer(kubeClient, 0)
	informerFactory := informers.NewSharedInformerFactory(kubeClient, 0)
	nodeInformer := informerFactory.Core().V1().Nodes()
	....
	rc.ScheduledPodsHasSynced = podInformer.Informer().HasSynced
	// scheduled pod cache
	podInformer.Informer().AddEventHandler(
		cache.FilteringResourceEventHandler{
			FilterFunc: func(obj interface{}) bool {
				switch t := obj.(type) {
				case *v1.Pod:
					return assignedNonTerminatedPod(t)
				case cache.DeletedFinalStateUnknown:
					if pod, ok := t.Obj.(*v1.Pod); ok {
						return assignedNonTerminatedPod(pod)
					}
					runtime.HandleError(fmt.Errorf("unable to convert object %T to *v1.Pod in %T", obj, rc))
					return false
				default:
					runtime.HandleError(fmt.Errorf("unable to handle object in %T: %T", rc, obj))
					return false
				}
			},
			Handler: cache.ResourceEventHandlerFuncs{
				AddFunc:    rc.addPodToCache,
				UpdateFunc: rc.updatePodInCache,
				DeleteFunc: rc.deletePodFromCache,
			},
		},
	)

	nodeInformer.Informer().AddEventHandler(
		cache.ResourceEventHandlerFuncs{
			AddFunc:    rc.addNodeToCache,
			UpdateFunc: rc.updateNodeInCache,
			DeleteFunc: rc.deleteNodeFromCache,
		},
	)

	rc.NodeLister = nodeInformer.Lister()
	rc.PodLister = podInformer.Lister()
	go podInformer.Informer().Run(stopCh)
	go nodeInformer.Informer().Run(stopCh)
	rc.InformerFactory.Start(stopCh)
	...

Does this PR introduce a user-facing change?

NO

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[k8s-ci-robot]

Hi @kitianFresh. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[kitianFresh]

/ok-to-test

[k8s-ci-robot]

@kitianFresh: Cannot trigger testing until a trusted user reviews the PR and leaves an /ok-to-test message.

In response to this:

/ok-to-test

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[coderanger]

/sig api-machinery
/ok-to-test

[aojea]

is not the intention of the user to run 2 informers on your example?

/assign @wojtek-t @deads2k

[kitianFresh]

is not the intention of the user to run 2 informers on your example?

I think we should avoid the user to run the informer more than once because some times the user maybe use the informer by wrong way, we should avoid this condition. if we do not, the informer may run many times but the program is ok, but the resource consume and program is not ok, you can not found the reason.

[fedebongio]

/triage accepted

[wojtek-t]

/release-note-none

/lgtm
/approve

Thanks!

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: kitianFresh, wojtek-t

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/retest

[kitianFresh]

/release-note-none

/lgtm
/approve

Thanks!

Thanks for reviewing.