Merge pull request #62563 from devdattakulkarni/client-go-details

Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Updated README to include client-go<->controller diagram

The sample-controller makes extensive use of various mechanisms
available in client-go. For writing custom controllers/operators
it will be helpful if there is precise description of how the
client-go library works and how/where it interfaces with
custom controller code.

Recently we published a blog post with these details here:

https://medium.com/@cloudark/kubernetes-custom-controllers-b6c7d0668fdf

This patch includes the diagram from the post, as was recommended
by @sttts on https://github.com/kubernetes/sample-controller/issues/13

**What this PR does / why we need it**:

**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Fixes #

**Special notes for your reviewer**:

**Release note**:

```release-note

```

Kubernetes-commit: 773def0194ecc1cd845ea9a01da761d5a0390e6e

vendor/k8s.io/client-go/util/workqueue/delaying_queue.go

@@ -45,7 +45,7 @@ func newDelayingQueue(clock clock.Clock, name string) DelayingInterface {
 	ret := &delayingType{
 		Interface:       NewNamed(name),
 		clock:           clock,
-		heartbeat:       clock.Tick(maxWait),
+		heartbeat:       clock.NewTicker(maxWait),
 		stopCh:          make(chan struct{}),
 		waitingForAddCh: make(chan *waitFor, 1000),
 		metrics:         newRetryMetrics(name),
@@ -67,10 +67,7 @@ type delayingType struct {
 	stopCh chan struct{}
 
 	// heartbeat ensures we wait no more than maxWait before firing
-	//
-	// TODO: replace with Ticker (and add to clock) so this can be cleaned up.
-	// clock.Tick will leak.
-	heartbeat <-chan time.Time
+	heartbeat clock.Ticker
 
 	// waitingForAddCh is a buffered channel that feeds waitingForAdd
 	waitingForAddCh chan *waitFor
@@ -138,6 +135,7 @@ func (pq waitForPriorityQueue) Peek() interface{} {
 func (q *delayingType) ShutDown() {
 	q.Interface.ShutDown()
 	close(q.stopCh)
+	q.heartbeat.Stop()
 }
 
 // AddAfter adds the given item to the work queue after the given delay
@@ -209,7 +207,7 @@ func (q *delayingType) waitingLoop() {
 		case <-q.stopCh:
 			return
 
-		case <-q.heartbeat:
+		case <-q.heartbeat.C():
 			// continue the loop, which will add ready items
 
 		case <-nextReadyAt: