// ignore nestedpendingoperations.IsAlreadyExists and exponentialbackoff.IsExponentialBackoff errors, they are expected.
func isExpectedError(err error) bool {
	return nestedpendingoperations.IsAlreadyExists(err) || exponentialbackoff.IsExponentialBackoff(err)
}

// MountVolume Func
// Avoid executing mount/map from multiple pods referencing the
// same volume in parallel
podName := nestedpendingoperations.EmptyUniquePodName

// TODO: remove this -- not necessary
if !volumeToMount.PluginIsAttachable && !volumeToMount.PluginIsDeviceMountable {
	// volume plugins which are Non-attachable and Non-deviceMountable can execute mount for multiple pods
	// referencing the same volume in parallel
	podName = util.GetUniquePodName(volumeToMount.Pod)
}

// TODO mount_device
return oe.pendingOperations.Run(
		volumeToMount.VolumeName, podName, "" /* nodeName */, generatedOperations)

// UnmountVolume Func
// All volume plugins can execute unmount/unmap for multiple pods referencing the
	// same volume in parallel
	podName := volumetypes.UniquePodName(volumeToUnmount.PodUID)

	return oe.pendingOperations.Run(
		volumeToUnmount.VolumeName, podName, "" /* nodeName */, generatedOperations)

// This is an internal function and caller should acquire and release the lock
func (grm *nestedPendingOperations) isOperationExists(key operationKey) (bool, int) {

	// If volumeName is empty, operation can be executed concurrently
	if key.volumeName == EmptyUniqueVolumeName {
		return false, -1
	}

	for previousOpIndex, previousOp := range grm.operations {
		volumeNameMatch := previousOp.key.volumeName == key.volumeName

		podNameMatch := previousOp.key.podName == EmptyUniquePodName ||
			key.podName == EmptyUniquePodName ||
			previousOp.key.podName == key.podName

		nodeNameMatch := previousOp.key.nodeName == EmptyNodeName ||
			key.nodeName == EmptyNodeName ||
			previousOp.key.nodeName == key.nodeName

		if volumeNameMatch && podNameMatch && nodeNameMatch {
			return true, previousOpIndex
		}
	}

	return false, -1
}

func (grm *nestedPendingOperations) Run(
	volumeName v1.UniqueVolumeName,
	podName volumetypes.UniquePodName,
	nodeName types.NodeName,
	generatedOperations volumetypes.GeneratedOperations) error {
	grm.lock.Lock()
	defer grm.lock.Unlock()

	opKey := operationKey{volumeName, podName, nodeName}

	opExists, previousOpIndex := grm.isOperationExists(opKey)
	if opExists {
		previousOp := grm.operations[previousOpIndex]
		// Operation already exists
		if previousOp.operationPending {
			// Operation is pending
			return NewAlreadyExistsError(opKey)
		}

		backOffErr := previousOp.expBackoff.SafeToRetry(fmt.Sprintf("%+v", opKey))
		if backOffErr != nil {
			if previousOp.operationName == generatedOperations.OperationName {
				return backOffErr
			}
			// previous operation and new operation are different. reset op. name and exp. backoff
			grm.operations[previousOpIndex].operationName = generatedOperations.OperationName
			grm.operations[previousOpIndex].expBackoff = exponentialbackoff.ExponentialBackoff{}
		}

		// Update existing operation to mark as pending.
		grm.operations[previousOpIndex].operationPending = true
		grm.operations[previousOpIndex].key = opKey
	} else {
		// Create a new operation
		grm.operations = append(grm.operations,
			operation{
				key:              opKey,
				operationPending: true,
				operationName:    generatedOperations.OperationName,
				expBackoff:       exponentialbackoff.ExponentialBackoff{},
			})
	}

	go func() (eventErr, detailedErr error) {
		// Handle unhandled panics (very unlikely)
		defer k8sRuntime.HandleCrash()
		// Handle completion of and error, if any, from operationFunc()
		defer grm.operationComplete(opKey, &detailedErr)
		return generatedOperations.Run()
	}()

	return nil
}