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/apimachinery/pkg/util/clock/clock.go

@@ -26,18 +26,12 @@ import (
 type Clock interface {
 	Now() time.Time
 	Since(time.Time) time.Duration
-	After(d time.Duration) <-chan time.Time
-	NewTimer(d time.Duration) Timer
-	Sleep(d time.Duration)
-	Tick(d time.Duration) <-chan time.Time
+	After(time.Duration) <-chan time.Time
+	NewTimer(time.Duration) Timer
+	Sleep(time.Duration)
+	NewTicker(time.Duration) Ticker
 }
 
-var (
-	_ = Clock(RealClock{})
-	_ = Clock(&FakeClock{})
-	_ = Clock(&IntervalClock{})
-)
-
 // RealClock really calls time.Now()
 type RealClock struct{}
 
@@ -62,8 +56,10 @@ func (RealClock) NewTimer(d time.Duration) Timer {
 	}
 }
 
-func (RealClock) Tick(d time.Duration) <-chan time.Time {
-	return time.Tick(d)
+func (RealClock) NewTicker(d time.Duration) Ticker {
+	return &realTicker{
+		ticker: time.NewTicker(d),
+	}
 }
 
 func (RealClock) Sleep(d time.Duration) {
@@ -137,7 +133,7 @@ func (f *FakeClock) NewTimer(d time.Duration) Timer {
 	return timer
 }
 
-func (f *FakeClock) Tick(d time.Duration) <-chan time.Time {
+func (f *FakeClock) NewTicker(d time.Duration) Ticker {
 	f.lock.Lock()
 	defer f.lock.Unlock()
 	tickTime := f.time.Add(d)
@@ -149,7 +145,9 @@ func (f *FakeClock) Tick(d time.Duration) <-chan time.Time {
 		destChan:      ch,
 	})
 
-	return ch
+	return &fakeTicker{
+		c: ch,
+	}
 }
 
 // Move clock by Duration, notify anyone that's called After, Tick, or NewTimer
@@ -242,8 +240,8 @@ func (*IntervalClock) NewTimer(d time.Duration) Timer {
 
 // Unimplemented, will panic.
 // TODO: make interval clock use FakeClock so this can be implemented.
-func (*IntervalClock) Tick(d time.Duration) <-chan time.Time {
-	panic("IntervalClock doesn't implement Tick")
+func (*IntervalClock) NewTicker(d time.Duration) Ticker {
+	panic("IntervalClock doesn't implement NewTicker")
 }
 
 func (*IntervalClock) Sleep(d time.Duration) {
@@ -258,11 +256,6 @@ type Timer interface {
 	Reset(d time.Duration) bool
 }
 
-var (
-	_ = Timer(&realTimer{})
-	_ = Timer(&fakeTimer{})
-)
-
 // realTimer is backed by an actual time.Timer.
 type realTimer struct {
 	timer *time.Timer
@@ -325,3 +318,31 @@ func (f *fakeTimer) Reset(d time.Duration) bool {
 
 	return active
 }
+
+type Ticker interface {
+	C() <-chan time.Time
+	Stop()
+}
+
+type realTicker struct {
+	ticker *time.Ticker
+}
+
+func (t *realTicker) C() <-chan time.Time {
+	return t.ticker.C
+}
+
+func (t *realTicker) Stop() {
+	t.ticker.Stop()
+}
+
+type fakeTicker struct {
+	c <-chan time.Time
+}
+
+func (t *fakeTicker) C() <-chan time.Time {
+	return t.c
+}
+
+func (t *fakeTicker) Stop() {
+}