chore(leader-election): modify leader-election comment to OnStoppedLeading callback is always called when the LeaderElector exits, even if it did not start leading.

Author: googs1025

staging/src/k8s.io/client-go/examples/leader-election/main.go

@@ -21,6 +21,7 @@ import (
 	"flag"
 	"os"
 	"os/signal"
+	"sync/atomic"
 	"syscall"
 	"time"
 
@@ -57,6 +58,7 @@ func main() {
 	var leaseLockName string
 	var leaseLockNamespace string
 	var id string
+	var startedLeading atomic.Bool
 
 	flag.StringVar(&kubeconfig, "kubeconfig", "", "absolute path to the kubeconfig file")
 	flag.StringVar(&id, "id", uuid.New().String(), "the holder identity name")
@@ -135,11 +137,24 @@ func main() {
 			OnStartedLeading: func(ctx context.Context) {
 				// we're notified when we start - this is where you would
 				// usually put your code
+				startedLeading.Store(true)
 				run(ctx)
 			},
 			OnStoppedLeading: func() {
-				// we can do cleanup here
+				// we can do cleanup here, but note that this callback is always called
+				// when the LeaderElector exits, even if it did not start leading.
+				// Therefore, we should check if we actually started leading before
+				// performing any cleanup operations to avoid unexpected behavior.
 				klog.Infof("leader lost: %s", id)
+
+				// Example check to ensure we only perform cleanup if we actually started leading
+				if startedLeading.Load() {
+					// Perform cleanup operations here
+					// For example, releasing resources, closing connections, etc.
+					klog.Info("Performing cleanup operations...")
+				} else {
+					klog.Info("No cleanup needed as we never started leading.")
+				}
 				os.Exit(0)
 			},
 			OnNewLeader: func(identity string) {

staging/src/k8s.io/client-go/tools/leaderelection/leaderelection.go

@@ -173,7 +173,10 @@ type LeaderElectionConfig struct {
 type LeaderCallbacks struct {
 	// OnStartedLeading is called when a LeaderElector client starts leading
 	OnStartedLeading func(context.Context)
-	// OnStoppedLeading is called when a LeaderElector client stops leading
+	// OnStoppedLeading is called when a LeaderElector client stops leading.
+	// This callback is always called when the LeaderElector exits, even if it did not start leading.
+	// Users should not assume that OnStoppedLeading is only called after OnStartedLeading.
+	// see: https://github.com/kubernetes/kubernetes/pull/127675#discussion_r1780059887
 	OnStoppedLeading func()
 	// OnNewLeader is called when the client observes a leader that is
 	// not the previously observed leader. This includes the first observed