✨return a bool from AddFinalizer and RemoveFinalizer

[hatfieldbrian]

When a finalizer is added or removed to an object, typically a client requests the object be updated on the server. Instead of making an update request unconditionally, it may be desirable to do so only when the object is modified, as an optimization. Since the add and remove finalizer routines do not return an indication whether a finalizer was add or removed respectively, a caller needs to determine this information some other way.

One way is to call ContainsFinalizer before calling AddFinalizer or RemoveFinalizer. But the time complexity of each of those routines is linear, resulting in two linear time functions when a finalizer is added or removed.

Another solution is to save the length of a the finalizer slice before calling add or remove finalizer and checking if the length is different upon return. This improves over the previous solution presuming len() of a slice is a constant time complexity operation.

This solution provided in this pull request simplifies further by not requiring the add or remove finalizer caller save slice length prior to call. Instead, the caller can simply call add or remove finalizer and if it returns true, then make the object update request.

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[varshaprasad96]

This addition does seem useful. But the other way which I could think of it is this:

1. Case 1: Finalizer is present and user wants it to be or finalizer is not present and user wants it removed - In this case, we can just use ConatinsFinalizer(), which is a linear operation of complexity O(n).
2. Case 2: When the finalizer is present and user wants it removed or vice versa: Here there needs to be an update to the object which needs to happen. As you have explained, we would have to use ContainsFinalizer + Add/RemoveFinalizer where there would be linear iteration twice. The complexity still remains linear. I am not sure if there would be much performance improvement by saving on one iteration, since updating the object is anyway a necessity.

We could still return a signal in Add or Remove Finalizer saying it has been updated or not, but I think boolean may not be apt. Returning false in AddFinalizer can also be interpreted by users that it has not been added to the object at all (though with proper docs we could explain that its just adding element to a list). We can instead maybe return an indication that it is already present.

type FinalizerStatus string

const (
	FinalizerUpdated    FinalizerStatus = "updated"
	FinalizerNotUpdated FinalizerStatus = "notupdated"
)

// AddFinalizer accepts an Object and adds the provided finalizer if not present.
func AddFinalizer(o client.Object, finalizer string) FinalizerStatus {
	f := o.GetFinalizers()
	for _, e := range f {
		if e == finalizer {
			return FinalizerUpdated
		}
	}
	o.SetFinalizers(append(f, finalizer))
	return FinalizerNotUpdated
}

However, this would be a breaking change. Also, I think the finalizer library already implements this in a better way. Would the library helpers satisfy your use case?

[hatfieldbrian]

Thanks for the fast response!

The finalizer library contains the primary issue I intend to solve: two linear iterations. For example, on lines 57 and 58 when a finalizer is added:

controller-runtime/pkg/finalizer/finalizer.go

Lines 57 to 58 in 4e7f0c9

	if dt := obj.GetDeletionTimestamp(); dt.IsZero() && !controllerutil.ContainsFinalizer(obj, key) {
	controllerutil.AddFinalizer(obj, key)

and lines 60 and 72 when one is removed. It does provide a bool res.Updated indicating whether the object was updated, but the reason I propose it be added is to avoid the two linear iterations issue it contains.

The functions are called AddFinalizer and RemoveFinalizer so I think it is intuitive and logical to interpret a boolean return code as an indication of whether each did, in this invocation, what its name indicates it should.

I would be ok with wrapping the boolean in a struct just to give it a name that the programmer must type. The library's struct has more than one field, making a structure more reasonable.

A string takes more work to match.

I propose naming the bool return value finalizersUpdated in the function signature to avoid misinterpretation. I updated the pull request with that solution. Thoughts?

[dmvolod]

It would be nice to keep old test "as is" without return validation to check for backward compatibility and create an additional tests for the new functionality validation

[hatfieldbrian]

A change was force-pushed that leaves the old tests unchanged and adds the new ones

[alvaroaleman]

/ok-to-test

[alvaroaleman]

I think you need to change the name, otherwise Ginko de-duplicates, the junit shows two instances of AddFinalizer and not four: https://prow.k8s.io/view/gs/kubernetes-jenkins/pr-logs/pull/kubernetes-sigs_controller-runtime/1636/pull-controller-runtime-test-master/1512120552670629888

[hatfieldbrian]

The new tests' descriptions have been changed to be different than the originals

[hatfieldbrian]

The apidiff job failed:

verifying api diff
invoking: 'hack/tools/bin/go-apidiff 954449d15797527d32eb9071c4b95b3e44c[26](https://prow.k8s.io/view/gs/kubernetes-jenkins/pr-logs/pull/kubernetes-sigs_controller-runtime/1636/pull-controller-runtime-apidiff-master/1514882772970246144#1:build-log.txt%3A26)115 --print-compatible'
sigs.k8s.io/controller-runtime/pkg/controller/controllerutil
  Incompatible changes:
  - AddFinalizer: changed from func(sigs.k8s.io/controller-runtime/pkg/client.Object, string) to func(sigs.k8s.io/controller-runtime/pkg/client.Object, string) bool
  - RemoveFinalizer: changed from func(sigs.k8s.io/controller-runtime/pkg/client.Object, string) to func(sigs.k8s.io/controller-runtime/pkg/client.Object, string) bool

It seems an API function may not be changed to return something, so new versions of the routines were defined named AddFinalizerV2 and RemoveFinalizerV2.

[alvaroaleman]

The apidiff job failed:

Yes, but it is not mandatory, it is only intending to inform us about compatibility breaks.

I don't think an added non-error return to a func that didn't return anything before can actually break anyone, because nothing can not be assigned to a variable nor returned and linters won't care either.

[alvaroaleman]

I meant to say: Please revert that and keep only one version of the funcs with the old name.

[k8s-ci-robot]

@hatfieldbrian: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-controller-runtime-apidiff-master	b8bc54a	link	false	/test pull-controller-runtime-apidiff-master

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[alvaroaleman]

thanks!

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: alvaroaleman, hatfieldbrian

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