// entropy as it shuffle-shards the request into a queue.  The
	// descr1 and descr2 values play no role in the logic but appear
	// in log messages.  This method always returns quickly (without
	// waiting for the request to be dequeued).  If this method
	// returns a nil Request value then caller should reject the
	// request and the returned bool indicates whether the QueueSet
	// was idle at the moment of the return.  Otherwise idle==false

func (q *traceBufQueue) push(buf *traceBuf) {
	buf.link = nil
	if q.head == nil {
		q.head = buf
	} else {
		q.tail.link = buf
	}
	q.tail = buf
}

// pop dequeues from the queue of buffers.
func (q *traceBufQueue) pop() *traceBuf {
	buf := q.head
	if buf == nil {
		return nil
	}
	q.head = buf.link
	if q.head == nil {
		q.tail = nil
	}
	buf.link = nil

	defer logger.Info("Shutting down CSR cleaner controller")

	for i := 0; i < workers; i++ {
		go wait.UntilWithContext(ctx, ccc.worker, pollingInterval)
	}

	<-ctx.Done()
}

// worker runs a thread that dequeues CSRs, handles them, and marks them done.
func (ccc *CSRCleanerController) worker(ctx context.Context) {
	logger := klog.FromContext(ctx)
	csrs, err := ccc.csrLister.List(labels.Everything())
	if err != nil {

// the last request in the queue. While the queue is empty and has a
// request executing: the last virtual finish time is the queue’s
// virtual start time. When a request is dequeued for service the
// queue’s virtual start time is advanced by G. When a request
// finishes being served, and the actual service time was S, the
// queue’s virtual start time is decremented by G - S.

		updatedRS, updateErr = c.UpdateStatus(context.TODO(), rs, metav1.UpdateOptions{})
		if updateErr == nil {
			return updatedRS, nil
		}
		// Stop retrying if we exceed statusUpdateRetries - the replicaSet will be requeued with a rate limit.
		if i >= statusUpdateRetries {
			break
		}
		// Update the ReplicaSet with the latest resource version for the next poll

// rollbackToTemplate compares the templates of the provided deployment and replica set and
// updates the deployment with the replica set template in case they are different. It also
// cleans up the rollback spec so subsequent requeues of the deployment won't end up in here.
func (dc *DeploymentController) rollbackToTemplate(ctx context.Context, d *apps.Deployment, rs *apps.ReplicaSet) (bool, error) {
	logger := klog.FromContext(ctx)
	performedRollback := false

	_, name, err := cache.SplitMetaNamespaceKey(key)
	if err != nil {
		return err
	}

	svm, err := rv.svmListers.Get(name)
	if apierrors.IsNotFound(err) {
		// no work to do, don't fail and requeue
		return nil
	}
	if err != nil {
		return err
	}
	// working with copy to avoid race condition between this and migration controller
	toBeProcessedSVM := svm.DeepCopy()

	// prepare completed
	defer close(cacheStmt.prepared)

	// Reason why cannot lock conn.PrepareContext
	// suppose the maxopen is 1, g1 is creating record and g2 is querying record.
	// 1. g1 begin tx, g1 is requeue because of waiting for the system call, now `db.ConnPool` db.numOpen == 1.
	// 2. g2 select lock `conn.PrepareContext(ctx, query)`, now db.numOpen == db.maxOpen , wait for release.

// interval should be used.
type ActionFunc func(TimedValue) (bool, time.Duration)

// Try processes the queue.Ends prematurely if RateLimiter forbids an
// action and leak is true. Otherwise, requeues the item to be
// processed. Each value is processed once if fn returns true,
// otherwise it is added back to the queue. The returned remaining is
// used to identify the minimum time to execute the next item in the

	_, name, err := cache.SplitMetaNamespaceKey(key)
	if err != nil {
		return err
	}

	svm, err := svmc.svmListers.Get(name)
	if apierrors.IsNotFound(err) {
		// no work to do, don't fail and requeue
		return nil
	}
	if err != nil {
		return err
	}
	// working with a copy to avoid race condition between this and resource version controller
	toBeProcessedSVM := svm.DeepCopy()