Merge pull request #112200 from pohly/client-go-shared-informer-factory-shutdown

client-go: support waiting for SharedInformerFactory shutdown

staging/src/k8s.io/apiextensions-apiserver/examples/client-go/pkg/client/informers/externalversions/factory.go

@@ -47,6 +47,11 @@ type sharedInformerFactory struct {
 	// startedInformers is used for tracking which informers have been started.
 	// This allows Start() to be called multiple times safely.
 	startedInformers map[reflect.Type]bool
+	// wg tracks how many goroutines were started.
+	wg sync.WaitGroup
+	// shuttingDown is true when Shutdown has been called. It may still be running
+	// because it needs to wait for goroutines.
+	shuttingDown bool
 }
 
 // WithCustomResyncConfig sets a custom resync period for the specified informer types.
@@ -107,20 +112,39 @@ func NewSharedInformerFactoryWithOptions(client versioned.Interface, defaultResy
 	return factory
 }
 
-// Start initializes all requested informers.
 func (f *sharedInformerFactory) Start(stopCh <-chan struct{}) {
 	f.lock.Lock()
 	defer f.lock.Unlock()
 
+	if f.shuttingDown {
+		return
+	}
+
 	for informerType, informer := range f.informers {
 		if !f.startedInformers[informerType] {
-			go informer.Run(stopCh)
+			f.wg.Add(1)
+			// We need a new variable in each loop iteration,
+			// otherwise the goroutine would use the loop variable
+			// and that keeps changing.
+			informer := informer
+			go func() {
+				defer f.wg.Done()
+				informer.Run(stopCh)
+			}()
 			f.startedInformers[informerType] = true
 		}
 	}
 }
 
-// WaitForCacheSync waits for all started informers' cache were synced.
+func (f *sharedInformerFactory) Shutdown() {
+	f.lock.Lock()
+	f.shuttingDown = true
+	f.lock.Unlock()
+
+	// Will return immediately if there is nothing to wait for.
+	f.wg.Wait()
+}
+
 func (f *sharedInformerFactory) WaitForCacheSync(stopCh <-chan struct{}) map[reflect.Type]bool {
 	informers := func() map[reflect.Type]cache.SharedIndexInformer {
 		f.lock.Lock()
@@ -167,11 +191,58 @@ func (f *sharedInformerFactory) InformerFor(obj runtime.Object, newFunc internal
 
 // SharedInformerFactory provides shared informers for resources in all known
 // API group versions.
+//
+// It is typically used like this:
+//
+//	ctx, cancel := context.Background()
+//	defer cancel()
+//	factory := NewSharedInformerFactory(client, resyncPeriod)
+//	defer factory.WaitForStop()    // Returns immediately if nothing was started.
+//	genericInformer := factory.ForResource(resource)
+//	typedInformer := factory.SomeAPIGroup().V1().SomeType()
+//	factory.Start(ctx.Done())          // Start processing these informers.
+//	synced := factory.WaitForCacheSync(ctx.Done())
+//	for v, ok := range synced {
+//	    if !ok {
+//	        fmt.Fprintf(os.Stderr, "caches failed to sync: %v", v)
+//	        return
+//	    }
+//	}
+//
+//	// Creating informers can also be created after Start, but then
+//	// Start must be called again:
+//	anotherGenericInformer := factory.ForResource(resource)
+//	factory.Start(ctx.Done())
 type SharedInformerFactory interface {
 	internalinterfaces.SharedInformerFactory
-	ForResource(resource schema.GroupVersionResource) (GenericInformer, error)
+
+	// Start initializes all requested informers. They are handled in goroutines
+	// which run until the stop channel gets closed.
+	Start(stopCh <-chan struct{})
+
+	// Shutdown marks a factory as shutting down. At that point no new
+	// informers can be started anymore and Start will return without
+	// doing anything.
+	//
+	// In addition, Shutdown blocks until all goroutines have terminated. For that
+	// to happen, the close channel(s) that they were started with must be closed,
+	// either before Shutdown gets called or while it is waiting.
+	//
+	// Shutdown may be called multiple times, even concurrently. All such calls will
+	// block until all goroutines have terminated.
+	Shutdown()
+
+	// WaitForCacheSync blocks until all started informers' caches were synced
+	// or the stop channel gets closed.
 	WaitForCacheSync(stopCh <-chan struct{}) map[reflect.Type]bool
 
+	// ForResource gives generic access to a shared informer of the matching type.
+	ForResource(resource schema.GroupVersionResource) (GenericInformer, error)
+
+	// InternalInformerFor returns the SharedIndexInformer for obj using an internal
+	// client.
+	InformerFor(obj runtime.Object, newFunc internalinterfaces.NewInformerFunc) cache.SharedIndexInformer
+
 	Cr() cr.Interface
 }
 

staging/src/k8s.io/apiextensions-apiserver/pkg/client/informers/externalversions/factory.go

@@ -47,6 +47,11 @@ type sharedInformerFactory struct {
 	// startedInformers is used for tracking which informers have been started.
 	// This allows Start() to be called multiple times safely.
 	startedInformers map[reflect.Type]bool
+	// wg tracks how many goroutines were started.
+	wg sync.WaitGroup
+	// shuttingDown is true when Shutdown has been called. It may still be running
+	// because it needs to wait for goroutines.
+	shuttingDown bool
 }
 
 // WithCustomResyncConfig sets a custom resync period for the specified informer types.
@@ -107,20 +112,39 @@ func NewSharedInformerFactoryWithOptions(client clientset.Interface, defaultResy
 	return factory
 }
 
-// Start initializes all requested informers.
 func (f *sharedInformerFactory) Start(stopCh <-chan struct{}) {
 	f.lock.Lock()
 	defer f.lock.Unlock()
 
+	if f.shuttingDown {
+		return
+	}
+
 	for informerType, informer := range f.informers {
 		if !f.startedInformers[informerType] {
-			go informer.Run(stopCh)
+			f.wg.Add(1)
+			// We need a new variable in each loop iteration,
+			// otherwise the goroutine would use the loop variable
+			// and that keeps changing.
+			informer := informer
+			go func() {
+				defer f.wg.Done()
+				informer.Run(stopCh)
+			}()
 			f.startedInformers[informerType] = true
 		}
 	}
 }
 
-// WaitForCacheSync waits for all started informers' cache were synced.
+func (f *sharedInformerFactory) Shutdown() {
+	f.lock.Lock()
+	f.shuttingDown = true
+	f.lock.Unlock()
+
+	// Will return immediately if there is nothing to wait for.
+	f.wg.Wait()
+}
+
 func (f *sharedInformerFactory) WaitForCacheSync(stopCh <-chan struct{}) map[reflect.Type]bool {
 	informers := func() map[reflect.Type]cache.SharedIndexInformer {
 		f.lock.Lock()
@@ -167,11 +191,58 @@ func (f *sharedInformerFactory) InformerFor(obj runtime.Object, newFunc internal
 
 // SharedInformerFactory provides shared informers for resources in all known
 // API group versions.
+//
+// It is typically used like this:
+//
+//	ctx, cancel := context.Background()
+//	defer cancel()
+//	factory := NewSharedInformerFactory(client, resyncPeriod)
+//	defer factory.WaitForStop()    // Returns immediately if nothing was started.
+//	genericInformer := factory.ForResource(resource)
+//	typedInformer := factory.SomeAPIGroup().V1().SomeType()
+//	factory.Start(ctx.Done())          // Start processing these informers.
+//	synced := factory.WaitForCacheSync(ctx.Done())
+//	for v, ok := range synced {
+//	    if !ok {
+//	        fmt.Fprintf(os.Stderr, "caches failed to sync: %v", v)
+//	        return
+//	    }
+//	}
+//
+//	// Creating informers can also be created after Start, but then
+//	// Start must be called again:
+//	anotherGenericInformer := factory.ForResource(resource)
+//	factory.Start(ctx.Done())
 type SharedInformerFactory interface {
 	internalinterfaces.SharedInformerFactory
-	ForResource(resource schema.GroupVersionResource) (GenericInformer, error)
+
+	// Start initializes all requested informers. They are handled in goroutines
+	// which run until the stop channel gets closed.
+	Start(stopCh <-chan struct{})
+
+	// Shutdown marks a factory as shutting down. At that point no new
+	// informers can be started anymore and Start will return without
+	// doing anything.
+	//
+	// In addition, Shutdown blocks until all goroutines have terminated. For that
+	// to happen, the close channel(s) that they were started with must be closed,
+	// either before Shutdown gets called or while it is waiting.
+	//
+	// Shutdown may be called multiple times, even concurrently. All such calls will
+	// block until all goroutines have terminated.
+	Shutdown()
+
+	// WaitForCacheSync blocks until all started informers' caches were synced
+	// or the stop channel gets closed.
 	WaitForCacheSync(stopCh <-chan struct{}) map[reflect.Type]bool
 
+	// ForResource gives generic access to a shared informer of the matching type.
+	ForResource(resource schema.GroupVersionResource) (GenericInformer, error)
+
+	// InternalInformerFor returns the SharedIndexInformer for obj using an internal
+	// client.
+	InformerFor(obj runtime.Object, newFunc internalinterfaces.NewInformerFunc) cache.SharedIndexInformer
+
 	Apiextensions() apiextensions.Interface
 }
 

staging/src/k8s.io/client-go/informers/factory.go

@@ -64,6 +64,11 @@ type sharedInformerFactory struct {
 	// startedInformers is used for tracking which informers have been started.
 	// This allows Start() to be called multiple times safely.
 	startedInformers map[reflect.Type]bool
+	// wg tracks how many goroutines were started.
+	wg sync.WaitGroup
+	// shuttingDown is true when Shutdown has been called. It may still be running
+	// because it needs to wait for goroutines.
+	shuttingDown bool
 }
 
 // WithCustomResyncConfig sets a custom resync period for the specified informer types.
@@ -124,20 +129,39 @@ func NewSharedInformerFactoryWithOptions(client kubernetes.Interface, defaultRes
 	return factory
 }
 
-// Start initializes all requested informers.
 func (f *sharedInformerFactory) Start(stopCh <-chan struct{}) {
 	f.lock.Lock()
 	defer f.lock.Unlock()
 
+	if f.shuttingDown {
+		return
+	}
+
 	for informerType, informer := range f.informers {
 		if !f.startedInformers[informerType] {
-			go informer.Run(stopCh)
+			f.wg.Add(1)
+			// We need a new variable in each loop iteration,
+			// otherwise the goroutine would use the loop variable
+			// and that keeps changing.
+			informer := informer
+			go func() {
+				defer f.wg.Done()
+				informer.Run(stopCh)
+			}()
 			f.startedInformers[informerType] = true
 		}
 	}
 }
 
-// WaitForCacheSync waits for all started informers' cache were synced.
+func (f *sharedInformerFactory) Shutdown() {
+	f.lock.Lock()
+	f.shuttingDown = true
+	f.lock.Unlock()
+
+	// Will return immediately if there is nothing to wait for.
+	f.wg.Wait()
+}
+
 func (f *sharedInformerFactory) WaitForCacheSync(stopCh <-chan struct{}) map[reflect.Type]bool {
 	informers := func() map[reflect.Type]cache.SharedIndexInformer {
 		f.lock.Lock()
@@ -184,11 +208,58 @@ func (f *sharedInformerFactory) InformerFor(obj runtime.Object, newFunc internal
 
 // SharedInformerFactory provides shared informers for resources in all known
 // API group versions.
+//
+// It is typically used like this:
+//
+//	ctx, cancel := context.Background()
+//	defer cancel()
+//	factory := NewSharedInformerFactory(client, resyncPeriod)
+//	defer factory.WaitForStop()    // Returns immediately if nothing was started.
+//	genericInformer := factory.ForResource(resource)
+//	typedInformer := factory.SomeAPIGroup().V1().SomeType()
+//	factory.Start(ctx.Done())          // Start processing these informers.
+//	synced := factory.WaitForCacheSync(ctx.Done())
+//	for v, ok := range synced {
+//	    if !ok {
+//	        fmt.Fprintf(os.Stderr, "caches failed to sync: %v", v)
+//	        return
+//	    }
+//	}
+//
+//	// Creating informers can also be created after Start, but then
+//	// Start must be called again:
+//	anotherGenericInformer := factory.ForResource(resource)
+//	factory.Start(ctx.Done())
 type SharedInformerFactory interface {
 	internalinterfaces.SharedInformerFactory
-	ForResource(resource schema.GroupVersionResource) (GenericInformer, error)
+
+	// Start initializes all requested informers. They are handled in goroutines
+	// which run until the stop channel gets closed.
+	Start(stopCh <-chan struct{})
+
+	// Shutdown marks a factory as shutting down. At that point no new
+	// informers can be started anymore and Start will return without
+	// doing anything.
+	//
+	// In addition, Shutdown blocks until all goroutines have terminated. For that
+	// to happen, the close channel(s) that they were started with must be closed,
+	// either before Shutdown gets called or while it is waiting.
+	//
+	// Shutdown may be called multiple times, even concurrently. All such calls will
+	// block until all goroutines have terminated.
+	Shutdown()
+
+	// WaitForCacheSync blocks until all started informers' caches were synced
+	// or the stop channel gets closed.
 	WaitForCacheSync(stopCh <-chan struct{}) map[reflect.Type]bool
 
+	// ForResource gives generic access to a shared informer of the matching type.
+	ForResource(resource schema.GroupVersionResource) (GenericInformer, error)
+
+	// InternalInformerFor returns the SharedIndexInformer for obj using an internal
+	// client.
+	InformerFor(obj runtime.Object, newFunc internalinterfaces.NewInformerFunc) cache.SharedIndexInformer
+
 	Admissionregistration() admissionregistration.Interface
 	Internal() apiserverinternal.Interface
 	Apps() apps.Interface

staging/src/k8s.io/code-generator/cmd/informer-gen/generators/factory.go

@@ -114,6 +114,11 @@ type sharedInformerFactory struct {
 	// startedInformers is used for tracking which informers have been started.
 	// This allows Start() to be called multiple times safely.
 	startedInformers map[{{.reflectType|raw}}]bool
+	// wg tracks how many goroutines were started.
+	wg sync.WaitGroup
+	// shuttingDown is true when Shutdown has been called. It may still be running
+	// because it needs to wait for goroutines.
+	shuttingDown bool
 }
 
 // WithCustomResyncConfig sets a custom resync period for the specified informer types.
@@ -174,20 +179,40 @@ func NewSharedInformerFactoryWithOptions(client {{.clientSetInterface|raw}}, def
 	return factory
 }
 
-// Start initializes all requested informers.
 func (f *sharedInformerFactory) Start(stopCh <-chan struct{}) {
-  f.lock.Lock()
-  defer f.lock.Unlock()
+	f.lock.Lock()
+	defer f.lock.Unlock()
 
-  for informerType, informer := range f.informers {
-    if !f.startedInformers[informerType] {
-      go informer.Run(stopCh)
-      f.startedInformers[informerType] = true
-    }
-  }
+	if f.shuttingDown {
+		return
+	}
+
+	for informerType, informer := range f.informers {
+		if !f.startedInformers[informerType] {
+			f.wg.Add(1)
+			// We need a new variable in each loop iteration,
+			// otherwise the goroutine would use the loop variable
+			// and that keeps changing.
+			informer := informer
+			go func() {
+				defer f.wg.Done()
+				informer.Run(stopCh)
+			}()
+			f.startedInformers[informerType] = true
+		}
+	}
+}
+
+func (f *sharedInformerFactory) Shutdown() {
+	f.lock.Lock()
+	f.shuttingDown = true
+	f.lock.Unlock()
+
+
+	// Will return immediately if there is nothing to wait for.
+	f.wg.Wait()
 }
 
-// WaitForCacheSync waits for all started informers' cache were synced.
 func (f *sharedInformerFactory) WaitForCacheSync(stopCh <-chan struct{}) map[reflect.Type]bool {
 	informers := func()map[reflect.Type]cache.SharedIndexInformer{
                f.lock.Lock()
@@ -237,11 +262,58 @@ func (f *sharedInformerFactory) InformerFor(obj {{.runtimeObject|raw}}, newFunc
 var sharedInformerFactoryInterface = `
 // SharedInformerFactory provides shared informers for resources in all known
 // API group versions.
+//
+// It is typically used like this:
+//
+//   ctx, cancel := context.Background()
+//   defer cancel()
+//   factory := NewSharedInformerFactory(client, resyncPeriod)
+//   defer factory.WaitForStop()    // Returns immediately if nothing was started.
+//   genericInformer := factory.ForResource(resource)
+//   typedInformer := factory.SomeAPIGroup().V1().SomeType()
+//   factory.Start(ctx.Done())          // Start processing these informers.
+//   synced := factory.WaitForCacheSync(ctx.Done())
+//   for v, ok := range synced {
+//       if !ok {
+//           fmt.Fprintf(os.Stderr, "caches failed to sync: %v", v)
+//           return
+//       }
+//   }
+//
+//   // Creating informers can also be created after Start, but then
+//   // Start must be called again:
+//   anotherGenericInformer := factory.ForResource(resource)
+//   factory.Start(ctx.Done())
 type SharedInformerFactory interface {
 	{{.informerFactoryInterface|raw}}
-	ForResource(resource {{.schemaGroupVersionResource|raw}}) (GenericInformer, error)
+
+	// Start initializes all requested informers. They are handled in goroutines
+	// which run until the stop channel gets closed.
+        Start(stopCh <-chan struct{})
+
+	// Shutdown marks a factory as shutting down. At that point no new
+	// informers can be started anymore and Start will return without
+	// doing anything.
+	//
+	// In addition, Shutdown blocks until all goroutines have terminated. For that
+	// to happen, the close channel(s) that they were started with must be closed,
+	// either before Shutdown gets called or while it is waiting.
+	//
+	// Shutdown may be called multiple times, even concurrently. All such calls will
+	// block until all goroutines have terminated.
+	Shutdown()
+
+	// WaitForCacheSync blocks until all started informers' caches were synced
+	// or the stop channel gets closed.
 	WaitForCacheSync(stopCh <-chan struct{}) map[reflect.Type]bool
 
+	// ForResource gives generic access to a shared informer of the matching type.
+	ForResource(resource {{.schemaGroupVersionResource|raw}}) (GenericInformer, error)
+
+	// InternalInformerFor returns the SharedIndexInformer for obj using an internal
+	// client.
+	InformerFor(obj {{.runtimeObject|raw}}, newFunc {{.interfacesNewInformerFunc|raw}}) {{.cacheSharedIndexInformer|raw}}
+
 	{{$gvInterfaces := .gvInterfaces}}
 	{{$gvGoNames := .gvGoNames}}
 	{{range $groupName, $group := .groupVersions}}{{index $gvGoNames $groupName}}() {{index $gvInterfaces $groupName|raw}}

staging/src/k8s.io/code-generator/examples/HyphenGroup/informers/externalversions/factory.go

@@ -47,6 +47,11 @@ type sharedInformerFactory struct {
 	// startedInformers is used for tracking which informers have been started.
 	// This allows Start() to be called multiple times safely.
 	startedInformers map[reflect.Type]bool
+	// wg tracks how many goroutines were started.
+	wg sync.WaitGroup
+	// shuttingDown is true when Shutdown has been called. It may still be running
+	// because it needs to wait for goroutines.
+	shuttingDown bool
 }
 
 // WithCustomResyncConfig sets a custom resync period for the specified informer types.
@@ -107,20 +112,39 @@ func NewSharedInformerFactoryWithOptions(client versioned.Interface, defaultResy
 	return factory
 }
 
-// Start initializes all requested informers.
 func (f *sharedInformerFactory) Start(stopCh <-chan struct{}) {
 	f.lock.Lock()
 	defer f.lock.Unlock()
 
+	if f.shuttingDown {
+		return
+	}
+
 	for informerType, informer := range f.informers {
 		if !f.startedInformers[informerType] {
-			go informer.Run(stopCh)
+			f.wg.Add(1)
+			// We need a new variable in each loop iteration,
+			// otherwise the goroutine would use the loop variable
+			// and that keeps changing.
+			informer := informer
+			go func() {
+				defer f.wg.Done()
+				informer.Run(stopCh)
+			}()
 			f.startedInformers[informerType] = true
 		}
 	}
 }
 
-// WaitForCacheSync waits for all started informers' cache were synced.
+func (f *sharedInformerFactory) Shutdown() {
+	f.lock.Lock()
+	f.shuttingDown = true
+	f.lock.Unlock()
+
+	// Will return immediately if there is nothing to wait for.
+	f.wg.Wait()
+}
+
 func (f *sharedInformerFactory) WaitForCacheSync(stopCh <-chan struct{}) map[reflect.Type]bool {
 	informers := func() map[reflect.Type]cache.SharedIndexInformer {
 		f.lock.Lock()
@@ -167,11 +191,58 @@ func (f *sharedInformerFactory) InformerFor(obj runtime.Object, newFunc internal
 
 // SharedInformerFactory provides shared informers for resources in all known
 // API group versions.
+//
+// It is typically used like this:
+//
+//	ctx, cancel := context.Background()
+//	defer cancel()
+//	factory := NewSharedInformerFactory(client, resyncPeriod)
+//	defer factory.WaitForStop()    // Returns immediately if nothing was started.
+//	genericInformer := factory.ForResource(resource)
+//	typedInformer := factory.SomeAPIGroup().V1().SomeType()
+//	factory.Start(ctx.Done())          // Start processing these informers.
+//	synced := factory.WaitForCacheSync(ctx.Done())
+//	for v, ok := range synced {
+//	    if !ok {
+//	        fmt.Fprintf(os.Stderr, "caches failed to sync: %v", v)
+//	        return
+//	    }
+//	}
+//
+//	// Creating informers can also be created after Start, but then
+//	// Start must be called again:
+//	anotherGenericInformer := factory.ForResource(resource)
+//	factory.Start(ctx.Done())
 type SharedInformerFactory interface {
 	internalinterfaces.SharedInformerFactory
-	ForResource(resource schema.GroupVersionResource) (GenericInformer, error)
+
+	// Start initializes all requested informers. They are handled in goroutines
+	// which run until the stop channel gets closed.
+	Start(stopCh <-chan struct{})
+
+	// Shutdown marks a factory as shutting down. At that point no new
+	// informers can be started anymore and Start will return without
+	// doing anything.
+	//
+	// In addition, Shutdown blocks until all goroutines have terminated. For that
+	// to happen, the close channel(s) that they were started with must be closed,
+	// either before Shutdown gets called or while it is waiting.
+	//
+	// Shutdown may be called multiple times, even concurrently. All such calls will
+	// block until all goroutines have terminated.
+	Shutdown()
+
+	// WaitForCacheSync blocks until all started informers' caches were synced
+	// or the stop channel gets closed.
 	WaitForCacheSync(stopCh <-chan struct{}) map[reflect.Type]bool
 
+	// ForResource gives generic access to a shared informer of the matching type.
+	ForResource(resource schema.GroupVersionResource) (GenericInformer, error)
+
+	// InternalInformerFor returns the SharedIndexInformer for obj using an internal
+	// client.
+	InformerFor(obj runtime.Object, newFunc internalinterfaces.NewInformerFunc) cache.SharedIndexInformer
+
 	ExampleGroup() example.Interface
 }
 

staging/src/k8s.io/code-generator/examples/MixedCase/informers/externalversions/factory.go

@@ -47,6 +47,11 @@ type sharedInformerFactory struct {
 	// startedInformers is used for tracking which informers have been started.
 	// This allows Start() to be called multiple times safely.
 	startedInformers map[reflect.Type]bool
+	// wg tracks how many goroutines were started.
+	wg sync.WaitGroup
+	// shuttingDown is true when Shutdown has been called. It may still be running
+	// because it needs to wait for goroutines.
+	shuttingDown bool
 }
 
 // WithCustomResyncConfig sets a custom resync period for the specified informer types.
@@ -107,20 +112,39 @@ func NewSharedInformerFactoryWithOptions(client versioned.Interface, defaultResy
 	return factory
 }
 
-// Start initializes all requested informers.
 func (f *sharedInformerFactory) Start(stopCh <-chan struct{}) {
 	f.lock.Lock()
 	defer f.lock.Unlock()
 
+	if f.shuttingDown {
+		return
+	}
+
 	for informerType, informer := range f.informers {
 		if !f.startedInformers[informerType] {
-			go informer.Run(stopCh)
+			f.wg.Add(1)
+			// We need a new variable in each loop iteration,
+			// otherwise the goroutine would use the loop variable
+			// and that keeps changing.
+			informer := informer
+			go func() {
+				defer f.wg.Done()
+				informer.Run(stopCh)
+			}()
 			f.startedInformers[informerType] = true
 		}
 	}
 }
 
-// WaitForCacheSync waits for all started informers' cache were synced.
+func (f *sharedInformerFactory) Shutdown() {
+	f.lock.Lock()
+	f.shuttingDown = true
+	f.lock.Unlock()
+
+	// Will return immediately if there is nothing to wait for.
+	f.wg.Wait()
+}
+
 func (f *sharedInformerFactory) WaitForCacheSync(stopCh <-chan struct{}) map[reflect.Type]bool {
 	informers := func() map[reflect.Type]cache.SharedIndexInformer {
 		f.lock.Lock()
@@ -167,11 +191,58 @@ func (f *sharedInformerFactory) InformerFor(obj runtime.Object, newFunc internal
 
 // SharedInformerFactory provides shared informers for resources in all known
 // API group versions.
+//
+// It is typically used like this:
+//
+//	ctx, cancel := context.Background()
+//	defer cancel()
+//	factory := NewSharedInformerFactory(client, resyncPeriod)
+//	defer factory.WaitForStop()    // Returns immediately if nothing was started.
+//	genericInformer := factory.ForResource(resource)
+//	typedInformer := factory.SomeAPIGroup().V1().SomeType()
+//	factory.Start(ctx.Done())          // Start processing these informers.
+//	synced := factory.WaitForCacheSync(ctx.Done())
+//	for v, ok := range synced {
+//	    if !ok {
+//	        fmt.Fprintf(os.Stderr, "caches failed to sync: %v", v)
+//	        return
+//	    }
+//	}
+//
+//	// Creating informers can also be created after Start, but then
+//	// Start must be called again:
+//	anotherGenericInformer := factory.ForResource(resource)
+//	factory.Start(ctx.Done())
 type SharedInformerFactory interface {
 	internalinterfaces.SharedInformerFactory
-	ForResource(resource schema.GroupVersionResource) (GenericInformer, error)
+
+	// Start initializes all requested informers. They are handled in goroutines
+	// which run until the stop channel gets closed.
+	Start(stopCh <-chan struct{})
+
+	// Shutdown marks a factory as shutting down. At that point no new
+	// informers can be started anymore and Start will return without
+	// doing anything.
+	//
+	// In addition, Shutdown blocks until all goroutines have terminated. For that
+	// to happen, the close channel(s) that they were started with must be closed,
+	// either before Shutdown gets called or while it is waiting.
+	//
+	// Shutdown may be called multiple times, even concurrently. All such calls will
+	// block until all goroutines have terminated.
+	Shutdown()
+
+	// WaitForCacheSync blocks until all started informers' caches were synced
+	// or the stop channel gets closed.
 	WaitForCacheSync(stopCh <-chan struct{}) map[reflect.Type]bool
 
+	// ForResource gives generic access to a shared informer of the matching type.
+	ForResource(resource schema.GroupVersionResource) (GenericInformer, error)
+
+	// InternalInformerFor returns the SharedIndexInformer for obj using an internal
+	// client.
+	InformerFor(obj runtime.Object, newFunc internalinterfaces.NewInformerFunc) cache.SharedIndexInformer
+
 	Example() example.Interface
 }
 

staging/src/k8s.io/code-generator/examples/apiserver/informers/externalversions/factory.go

@@ -49,6 +49,11 @@ type sharedInformerFactory struct {
 	// startedInformers is used for tracking which informers have been started.
 	// This allows Start() to be called multiple times safely.
 	startedInformers map[reflect.Type]bool
+	// wg tracks how many goroutines were started.
+	wg sync.WaitGroup
+	// shuttingDown is true when Shutdown has been called. It may still be running
+	// because it needs to wait for goroutines.
+	shuttingDown bool
 }
 
 // WithCustomResyncConfig sets a custom resync period for the specified informer types.
@@ -109,20 +114,39 @@ func NewSharedInformerFactoryWithOptions(client versioned.Interface, defaultResy
 	return factory
 }
 
-// Start initializes all requested informers.
 func (f *sharedInformerFactory) Start(stopCh <-chan struct{}) {
 	f.lock.Lock()
 	defer f.lock.Unlock()
 
+	if f.shuttingDown {
+		return
+	}
+
 	for informerType, informer := range f.informers {
 		if !f.startedInformers[informerType] {
-			go informer.Run(stopCh)
+			f.wg.Add(1)
+			// We need a new variable in each loop iteration,
+			// otherwise the goroutine would use the loop variable
+			// and that keeps changing.
+			informer := informer
+			go func() {
+				defer f.wg.Done()
+				informer.Run(stopCh)
+			}()
 			f.startedInformers[informerType] = true
 		}
 	}
 }
 
-// WaitForCacheSync waits for all started informers' cache were synced.
+func (f *sharedInformerFactory) Shutdown() {
+	f.lock.Lock()
+	f.shuttingDown = true
+	f.lock.Unlock()
+
+	// Will return immediately if there is nothing to wait for.
+	f.wg.Wait()
+}
+
 func (f *sharedInformerFactory) WaitForCacheSync(stopCh <-chan struct{}) map[reflect.Type]bool {
 	informers := func() map[reflect.Type]cache.SharedIndexInformer {
 		f.lock.Lock()
@@ -169,11 +193,58 @@ func (f *sharedInformerFactory) InformerFor(obj runtime.Object, newFunc internal
 
 // SharedInformerFactory provides shared informers for resources in all known
 // API group versions.
+//
+// It is typically used like this:
+//
+//	ctx, cancel := context.Background()
+//	defer cancel()
+//	factory := NewSharedInformerFactory(client, resyncPeriod)
+//	defer factory.WaitForStop()    // Returns immediately if nothing was started.
+//	genericInformer := factory.ForResource(resource)
+//	typedInformer := factory.SomeAPIGroup().V1().SomeType()
+//	factory.Start(ctx.Done())          // Start processing these informers.
+//	synced := factory.WaitForCacheSync(ctx.Done())
+//	for v, ok := range synced {
+//	    if !ok {
+//	        fmt.Fprintf(os.Stderr, "caches failed to sync: %v", v)
+//	        return
+//	    }
+//	}
+//
+//	// Creating informers can also be created after Start, but then
+//	// Start must be called again:
+//	anotherGenericInformer := factory.ForResource(resource)
+//	factory.Start(ctx.Done())
 type SharedInformerFactory interface {
 	internalinterfaces.SharedInformerFactory
-	ForResource(resource schema.GroupVersionResource) (GenericInformer, error)
+
+	// Start initializes all requested informers. They are handled in goroutines
+	// which run until the stop channel gets closed.
+	Start(stopCh <-chan struct{})
+
+	// Shutdown marks a factory as shutting down. At that point no new
+	// informers can be started anymore and Start will return without
+	// doing anything.
+	//
+	// In addition, Shutdown blocks until all goroutines have terminated. For that
+	// to happen, the close channel(s) that they were started with must be closed,
+	// either before Shutdown gets called or while it is waiting.
+	//
+	// Shutdown may be called multiple times, even concurrently. All such calls will
+	// block until all goroutines have terminated.
+	Shutdown()
+
+	// WaitForCacheSync blocks until all started informers' caches were synced
+	// or the stop channel gets closed.
 	WaitForCacheSync(stopCh <-chan struct{}) map[reflect.Type]bool
 
+	// ForResource gives generic access to a shared informer of the matching type.
+	ForResource(resource schema.GroupVersionResource) (GenericInformer, error)
+
+	// InternalInformerFor returns the SharedIndexInformer for obj using an internal
+	// client.
+	InformerFor(obj runtime.Object, newFunc internalinterfaces.NewInformerFunc) cache.SharedIndexInformer
+
 	Example() example.Interface
 	SecondExample() example2.Interface
 	ThirdExample() example3io.Interface

staging/src/k8s.io/code-generator/examples/apiserver/informers/internalversion/factory.go

@@ -49,6 +49,11 @@ type sharedInformerFactory struct {
 	// startedInformers is used for tracking which informers have been started.
 	// This allows Start() to be called multiple times safely.
 	startedInformers map[reflect.Type]bool
+	// wg tracks how many goroutines were started.
+	wg sync.WaitGroup
+	// shuttingDown is true when Shutdown has been called. It may still be running
+	// because it needs to wait for goroutines.
+	shuttingDown bool
 }
 
 // WithCustomResyncConfig sets a custom resync period for the specified informer types.
@@ -109,20 +114,39 @@ func NewSharedInformerFactoryWithOptions(client internalversion.Interface, defau
 	return factory
 }
 
-// Start initializes all requested informers.
 func (f *sharedInformerFactory) Start(stopCh <-chan struct{}) {
 	f.lock.Lock()
 	defer f.lock.Unlock()
 
+	if f.shuttingDown {
+		return
+	}
+
 	for informerType, informer := range f.informers {
 		if !f.startedInformers[informerType] {
-			go informer.Run(stopCh)
+			f.wg.Add(1)
+			// We need a new variable in each loop iteration,
+			// otherwise the goroutine would use the loop variable
+			// and that keeps changing.
+			informer := informer
+			go func() {
+				defer f.wg.Done()
+				informer.Run(stopCh)
+			}()
 			f.startedInformers[informerType] = true
 		}
 	}
 }
 
-// WaitForCacheSync waits for all started informers' cache were synced.
+func (f *sharedInformerFactory) Shutdown() {
+	f.lock.Lock()
+	f.shuttingDown = true
+	f.lock.Unlock()
+
+	// Will return immediately if there is nothing to wait for.
+	f.wg.Wait()
+}
+
 func (f *sharedInformerFactory) WaitForCacheSync(stopCh <-chan struct{}) map[reflect.Type]bool {
 	informers := func() map[reflect.Type]cache.SharedIndexInformer {
 		f.lock.Lock()
@@ -169,11 +193,58 @@ func (f *sharedInformerFactory) InformerFor(obj runtime.Object, newFunc internal
 
 // SharedInformerFactory provides shared informers for resources in all known
 // API group versions.
+//
+// It is typically used like this:
+//
+//	ctx, cancel := context.Background()
+//	defer cancel()
+//	factory := NewSharedInformerFactory(client, resyncPeriod)
+//	defer factory.WaitForStop()    // Returns immediately if nothing was started.
+//	genericInformer := factory.ForResource(resource)
+//	typedInformer := factory.SomeAPIGroup().V1().SomeType()
+//	factory.Start(ctx.Done())          // Start processing these informers.
+//	synced := factory.WaitForCacheSync(ctx.Done())
+//	for v, ok := range synced {
+//	    if !ok {
+//	        fmt.Fprintf(os.Stderr, "caches failed to sync: %v", v)
+//	        return
+//	    }
+//	}
+//
+//	// Creating informers can also be created after Start, but then
+//	// Start must be called again:
+//	anotherGenericInformer := factory.ForResource(resource)
+//	factory.Start(ctx.Done())
 type SharedInformerFactory interface {
 	internalinterfaces.SharedInformerFactory
-	ForResource(resource schema.GroupVersionResource) (GenericInformer, error)
+
+	// Start initializes all requested informers. They are handled in goroutines
+	// which run until the stop channel gets closed.
+	Start(stopCh <-chan struct{})
+
+	// Shutdown marks a factory as shutting down. At that point no new
+	// informers can be started anymore and Start will return without
+	// doing anything.
+	//
+	// In addition, Shutdown blocks until all goroutines have terminated. For that
+	// to happen, the close channel(s) that they were started with must be closed,
+	// either before Shutdown gets called or while it is waiting.
+	//
+	// Shutdown may be called multiple times, even concurrently. All such calls will
+	// block until all goroutines have terminated.
+	Shutdown()
+
+	// WaitForCacheSync blocks until all started informers' caches were synced
+	// or the stop channel gets closed.
 	WaitForCacheSync(stopCh <-chan struct{}) map[reflect.Type]bool
 
+	// ForResource gives generic access to a shared informer of the matching type.
+	ForResource(resource schema.GroupVersionResource) (GenericInformer, error)
+
+	// InternalInformerFor returns the SharedIndexInformer for obj using an internal
+	// client.
+	InformerFor(obj runtime.Object, newFunc internalinterfaces.NewInformerFunc) cache.SharedIndexInformer
+
 	Example() example.Interface
 	SecondExample() example2.Interface
 	ThirdExample() example3io.Interface

staging/src/k8s.io/code-generator/examples/crd/informers/externalversions/factory.go

@@ -48,6 +48,11 @@ type sharedInformerFactory struct {
 	// startedInformers is used for tracking which informers have been started.
 	// This allows Start() to be called multiple times safely.
 	startedInformers map[reflect.Type]bool
+	// wg tracks how many goroutines were started.
+	wg sync.WaitGroup
+	// shuttingDown is true when Shutdown has been called. It may still be running
+	// because it needs to wait for goroutines.
+	shuttingDown bool
 }
 
 // WithCustomResyncConfig sets a custom resync period for the specified informer types.
@@ -108,20 +113,39 @@ func NewSharedInformerFactoryWithOptions(client versioned.Interface, defaultResy
 	return factory
 }
 
-// Start initializes all requested informers.
 func (f *sharedInformerFactory) Start(stopCh <-chan struct{}) {
 	f.lock.Lock()
 	defer f.lock.Unlock()
 
+	if f.shuttingDown {
+		return
+	}
+
 	for informerType, informer := range f.informers {
 		if !f.startedInformers[informerType] {
-			go informer.Run(stopCh)
+			f.wg.Add(1)
+			// We need a new variable in each loop iteration,
+			// otherwise the goroutine would use the loop variable
+			// and that keeps changing.
+			informer := informer
+			go func() {
+				defer f.wg.Done()
+				informer.Run(stopCh)
+			}()
 			f.startedInformers[informerType] = true
 		}
 	}
 }
 
-// WaitForCacheSync waits for all started informers' cache were synced.
+func (f *sharedInformerFactory) Shutdown() {
+	f.lock.Lock()
+	f.shuttingDown = true
+	f.lock.Unlock()
+
+	// Will return immediately if there is nothing to wait for.
+	f.wg.Wait()
+}
+
 func (f *sharedInformerFactory) WaitForCacheSync(stopCh <-chan struct{}) map[reflect.Type]bool {
 	informers := func() map[reflect.Type]cache.SharedIndexInformer {
 		f.lock.Lock()
@@ -168,11 +192,58 @@ func (f *sharedInformerFactory) InformerFor(obj runtime.Object, newFunc internal
 
 // SharedInformerFactory provides shared informers for resources in all known
 // API group versions.
+//
+// It is typically used like this:
+//
+//	ctx, cancel := context.Background()
+//	defer cancel()
+//	factory := NewSharedInformerFactory(client, resyncPeriod)
+//	defer factory.WaitForStop()    // Returns immediately if nothing was started.
+//	genericInformer := factory.ForResource(resource)
+//	typedInformer := factory.SomeAPIGroup().V1().SomeType()
+//	factory.Start(ctx.Done())          // Start processing these informers.
+//	synced := factory.WaitForCacheSync(ctx.Done())
+//	for v, ok := range synced {
+//	    if !ok {
+//	        fmt.Fprintf(os.Stderr, "caches failed to sync: %v", v)
+//	        return
+//	    }
+//	}
+//
+//	// Creating informers can also be created after Start, but then
+//	// Start must be called again:
+//	anotherGenericInformer := factory.ForResource(resource)
+//	factory.Start(ctx.Done())
 type SharedInformerFactory interface {
 	internalinterfaces.SharedInformerFactory
-	ForResource(resource schema.GroupVersionResource) (GenericInformer, error)
+
+	// Start initializes all requested informers. They are handled in goroutines
+	// which run until the stop channel gets closed.
+	Start(stopCh <-chan struct{})
+
+	// Shutdown marks a factory as shutting down. At that point no new
+	// informers can be started anymore and Start will return without
+	// doing anything.
+	//
+	// In addition, Shutdown blocks until all goroutines have terminated. For that
+	// to happen, the close channel(s) that they were started with must be closed,
+	// either before Shutdown gets called or while it is waiting.
+	//
+	// Shutdown may be called multiple times, even concurrently. All such calls will
+	// block until all goroutines have terminated.
+	Shutdown()
+
+	// WaitForCacheSync blocks until all started informers' caches were synced
+	// or the stop channel gets closed.
 	WaitForCacheSync(stopCh <-chan struct{}) map[reflect.Type]bool
 
+	// ForResource gives generic access to a shared informer of the matching type.
+	ForResource(resource schema.GroupVersionResource) (GenericInformer, error)
+
+	// InternalInformerFor returns the SharedIndexInformer for obj using an internal
+	// client.
+	InformerFor(obj runtime.Object, newFunc internalinterfaces.NewInformerFunc) cache.SharedIndexInformer
+
 	Example() example.Interface
 	SecondExample() example2.Interface
 }

staging/src/k8s.io/kube-aggregator/pkg/client/informers/externalversions/factory.go

@@ -47,6 +47,11 @@ type sharedInformerFactory struct {
 	// startedInformers is used for tracking which informers have been started.
 	// This allows Start() to be called multiple times safely.
 	startedInformers map[reflect.Type]bool
+	// wg tracks how many goroutines were started.
+	wg sync.WaitGroup
+	// shuttingDown is true when Shutdown has been called. It may still be running
+	// because it needs to wait for goroutines.
+	shuttingDown bool
 }
 
 // WithCustomResyncConfig sets a custom resync period for the specified informer types.
@@ -107,20 +112,39 @@ func NewSharedInformerFactoryWithOptions(client clientset.Interface, defaultResy
 	return factory
 }
 
-// Start initializes all requested informers.
 func (f *sharedInformerFactory) Start(stopCh <-chan struct{}) {
 	f.lock.Lock()
 	defer f.lock.Unlock()
 
+	if f.shuttingDown {
+		return
+	}
+
 	for informerType, informer := range f.informers {
 		if !f.startedInformers[informerType] {
-			go informer.Run(stopCh)
+			f.wg.Add(1)
+			// We need a new variable in each loop iteration,
+			// otherwise the goroutine would use the loop variable
+			// and that keeps changing.
+			informer := informer
+			go func() {
+				defer f.wg.Done()
+				informer.Run(stopCh)
+			}()
 			f.startedInformers[informerType] = true
 		}
 	}
 }
 
-// WaitForCacheSync waits for all started informers' cache were synced.
+func (f *sharedInformerFactory) Shutdown() {
+	f.lock.Lock()
+	f.shuttingDown = true
+	f.lock.Unlock()
+
+	// Will return immediately if there is nothing to wait for.
+	f.wg.Wait()
+}
+
 func (f *sharedInformerFactory) WaitForCacheSync(stopCh <-chan struct{}) map[reflect.Type]bool {
 	informers := func() map[reflect.Type]cache.SharedIndexInformer {
 		f.lock.Lock()
@@ -167,11 +191,58 @@ func (f *sharedInformerFactory) InformerFor(obj runtime.Object, newFunc internal
 
 // SharedInformerFactory provides shared informers for resources in all known
 // API group versions.
+//
+// It is typically used like this:
+//
+//	ctx, cancel := context.Background()
+//	defer cancel()
+//	factory := NewSharedInformerFactory(client, resyncPeriod)
+//	defer factory.WaitForStop()    // Returns immediately if nothing was started.
+//	genericInformer := factory.ForResource(resource)
+//	typedInformer := factory.SomeAPIGroup().V1().SomeType()
+//	factory.Start(ctx.Done())          // Start processing these informers.
+//	synced := factory.WaitForCacheSync(ctx.Done())
+//	for v, ok := range synced {
+//	    if !ok {
+//	        fmt.Fprintf(os.Stderr, "caches failed to sync: %v", v)
+//	        return
+//	    }
+//	}
+//
+//	// Creating informers can also be created after Start, but then
+//	// Start must be called again:
+//	anotherGenericInformer := factory.ForResource(resource)
+//	factory.Start(ctx.Done())
 type SharedInformerFactory interface {
 	internalinterfaces.SharedInformerFactory
-	ForResource(resource schema.GroupVersionResource) (GenericInformer, error)
+
+	// Start initializes all requested informers. They are handled in goroutines
+	// which run until the stop channel gets closed.
+	Start(stopCh <-chan struct{})
+
+	// Shutdown marks a factory as shutting down. At that point no new
+	// informers can be started anymore and Start will return without
+	// doing anything.
+	//
+	// In addition, Shutdown blocks until all goroutines have terminated. For that
+	// to happen, the close channel(s) that they were started with must be closed,
+	// either before Shutdown gets called or while it is waiting.
+	//
+	// Shutdown may be called multiple times, even concurrently. All such calls will
+	// block until all goroutines have terminated.
+	Shutdown()
+
+	// WaitForCacheSync blocks until all started informers' caches were synced
+	// or the stop channel gets closed.
 	WaitForCacheSync(stopCh <-chan struct{}) map[reflect.Type]bool
 
+	// ForResource gives generic access to a shared informer of the matching type.
+	ForResource(resource schema.GroupVersionResource) (GenericInformer, error)
+
+	// InternalInformerFor returns the SharedIndexInformer for obj using an internal
+	// client.
+	InformerFor(obj runtime.Object, newFunc internalinterfaces.NewInformerFunc) cache.SharedIndexInformer
+
 	Apiregistration() apiregistration.Interface
 }
 

staging/src/k8s.io/sample-apiserver/pkg/generated/informers/externalversions/factory.go

@@ -47,6 +47,11 @@ type sharedInformerFactory struct {
 	// startedInformers is used for tracking which informers have been started.
 	// This allows Start() to be called multiple times safely.
 	startedInformers map[reflect.Type]bool
+	// wg tracks how many goroutines were started.
+	wg sync.WaitGroup
+	// shuttingDown is true when Shutdown has been called. It may still be running
+	// because it needs to wait for goroutines.
+	shuttingDown bool
 }
 
 // WithCustomResyncConfig sets a custom resync period for the specified informer types.
@@ -107,20 +112,39 @@ func NewSharedInformerFactoryWithOptions(client versioned.Interface, defaultResy
 	return factory
 }
 
-// Start initializes all requested informers.
 func (f *sharedInformerFactory) Start(stopCh <-chan struct{}) {
 	f.lock.Lock()
 	defer f.lock.Unlock()
 
+	if f.shuttingDown {
+		return
+	}
+
 	for informerType, informer := range f.informers {
 		if !f.startedInformers[informerType] {
-			go informer.Run(stopCh)
+			f.wg.Add(1)
+			// We need a new variable in each loop iteration,
+			// otherwise the goroutine would use the loop variable
+			// and that keeps changing.
+			informer := informer
+			go func() {
+				defer f.wg.Done()
+				informer.Run(stopCh)
+			}()
 			f.startedInformers[informerType] = true
 		}
 	}
 }
 
-// WaitForCacheSync waits for all started informers' cache were synced.
+func (f *sharedInformerFactory) Shutdown() {
+	f.lock.Lock()
+	f.shuttingDown = true
+	f.lock.Unlock()
+
+	// Will return immediately if there is nothing to wait for.
+	f.wg.Wait()
+}
+
 func (f *sharedInformerFactory) WaitForCacheSync(stopCh <-chan struct{}) map[reflect.Type]bool {
 	informers := func() map[reflect.Type]cache.SharedIndexInformer {
 		f.lock.Lock()
@@ -167,11 +191,58 @@ func (f *sharedInformerFactory) InformerFor(obj runtime.Object, newFunc internal
 
 // SharedInformerFactory provides shared informers for resources in all known
 // API group versions.
+//
+// It is typically used like this:
+//
+//	ctx, cancel := context.Background()
+//	defer cancel()
+//	factory := NewSharedInformerFactory(client, resyncPeriod)
+//	defer factory.WaitForStop()    // Returns immediately if nothing was started.
+//	genericInformer := factory.ForResource(resource)
+//	typedInformer := factory.SomeAPIGroup().V1().SomeType()
+//	factory.Start(ctx.Done())          // Start processing these informers.
+//	synced := factory.WaitForCacheSync(ctx.Done())
+//	for v, ok := range synced {
+//	    if !ok {
+//	        fmt.Fprintf(os.Stderr, "caches failed to sync: %v", v)
+//	        return
+//	    }
+//	}
+//
+//	// Creating informers can also be created after Start, but then
+//	// Start must be called again:
+//	anotherGenericInformer := factory.ForResource(resource)
+//	factory.Start(ctx.Done())
 type SharedInformerFactory interface {
 	internalinterfaces.SharedInformerFactory
-	ForResource(resource schema.GroupVersionResource) (GenericInformer, error)
+
+	// Start initializes all requested informers. They are handled in goroutines
+	// which run until the stop channel gets closed.
+	Start(stopCh <-chan struct{})
+
+	// Shutdown marks a factory as shutting down. At that point no new
+	// informers can be started anymore and Start will return without
+	// doing anything.
+	//
+	// In addition, Shutdown blocks until all goroutines have terminated. For that
+	// to happen, the close channel(s) that they were started with must be closed,
+	// either before Shutdown gets called or while it is waiting.
+	//
+	// Shutdown may be called multiple times, even concurrently. All such calls will
+	// block until all goroutines have terminated.
+	Shutdown()
+
+	// WaitForCacheSync blocks until all started informers' caches were synced
+	// or the stop channel gets closed.
 	WaitForCacheSync(stopCh <-chan struct{}) map[reflect.Type]bool
 
+	// ForResource gives generic access to a shared informer of the matching type.
+	ForResource(resource schema.GroupVersionResource) (GenericInformer, error)
+
+	// InternalInformerFor returns the SharedIndexInformer for obj using an internal
+	// client.
+	InformerFor(obj runtime.Object, newFunc internalinterfaces.NewInformerFunc) cache.SharedIndexInformer
+
 	Wardle() wardle.Interface
 }
 

staging/src/k8s.io/sample-controller/pkg/generated/informers/externalversions/factory.go

@@ -47,6 +47,11 @@ type sharedInformerFactory struct {
 	// startedInformers is used for tracking which informers have been started.
 	// This allows Start() to be called multiple times safely.
 	startedInformers map[reflect.Type]bool
+	// wg tracks how many goroutines were started.
+	wg sync.WaitGroup
+	// shuttingDown is true when Shutdown has been called. It may still be running
+	// because it needs to wait for goroutines.
+	shuttingDown bool
 }
 
 // WithCustomResyncConfig sets a custom resync period for the specified informer types.
@@ -107,20 +112,39 @@ func NewSharedInformerFactoryWithOptions(client versioned.Interface, defaultResy
 	return factory
 }
 
-// Start initializes all requested informers.
 func (f *sharedInformerFactory) Start(stopCh <-chan struct{}) {
 	f.lock.Lock()
 	defer f.lock.Unlock()
 
+	if f.shuttingDown {
+		return
+	}
+
 	for informerType, informer := range f.informers {
 		if !f.startedInformers[informerType] {
-			go informer.Run(stopCh)
+			f.wg.Add(1)
+			// We need a new variable in each loop iteration,
+			// otherwise the goroutine would use the loop variable
+			// and that keeps changing.
+			informer := informer
+			go func() {
+				defer f.wg.Done()
+				informer.Run(stopCh)
+			}()
 			f.startedInformers[informerType] = true
 		}
 	}
 }
 
-// WaitForCacheSync waits for all started informers' cache were synced.
+func (f *sharedInformerFactory) Shutdown() {
+	f.lock.Lock()
+	f.shuttingDown = true
+	f.lock.Unlock()
+
+	// Will return immediately if there is nothing to wait for.
+	f.wg.Wait()
+}
+
 func (f *sharedInformerFactory) WaitForCacheSync(stopCh <-chan struct{}) map[reflect.Type]bool {
 	informers := func() map[reflect.Type]cache.SharedIndexInformer {
 		f.lock.Lock()
@@ -167,11 +191,58 @@ func (f *sharedInformerFactory) InformerFor(obj runtime.Object, newFunc internal
 
 // SharedInformerFactory provides shared informers for resources in all known
 // API group versions.
+//
+// It is typically used like this:
+//
+//	ctx, cancel := context.Background()
+//	defer cancel()
+//	factory := NewSharedInformerFactory(client, resyncPeriod)
+//	defer factory.WaitForStop()    // Returns immediately if nothing was started.
+//	genericInformer := factory.ForResource(resource)
+//	typedInformer := factory.SomeAPIGroup().V1().SomeType()
+//	factory.Start(ctx.Done())          // Start processing these informers.
+//	synced := factory.WaitForCacheSync(ctx.Done())
+//	for v, ok := range synced {
+//	    if !ok {
+//	        fmt.Fprintf(os.Stderr, "caches failed to sync: %v", v)
+//	        return
+//	    }
+//	}
+//
+//	// Creating informers can also be created after Start, but then
+//	// Start must be called again:
+//	anotherGenericInformer := factory.ForResource(resource)
+//	factory.Start(ctx.Done())
 type SharedInformerFactory interface {
 	internalinterfaces.SharedInformerFactory
-	ForResource(resource schema.GroupVersionResource) (GenericInformer, error)
+
+	// Start initializes all requested informers. They are handled in goroutines
+	// which run until the stop channel gets closed.
+	Start(stopCh <-chan struct{})
+
+	// Shutdown marks a factory as shutting down. At that point no new
+	// informers can be started anymore and Start will return without
+	// doing anything.
+	//
+	// In addition, Shutdown blocks until all goroutines have terminated. For that
+	// to happen, the close channel(s) that they were started with must be closed,
+	// either before Shutdown gets called or while it is waiting.
+	//
+	// Shutdown may be called multiple times, even concurrently. All such calls will
+	// block until all goroutines have terminated.
+	Shutdown()
+
+	// WaitForCacheSync blocks until all started informers' caches were synced
+	// or the stop channel gets closed.
 	WaitForCacheSync(stopCh <-chan struct{}) map[reflect.Type]bool
 
+	// ForResource gives generic access to a shared informer of the matching type.
+	ForResource(resource schema.GroupVersionResource) (GenericInformer, error)
+
+	// InternalInformerFor returns the SharedIndexInformer for obj using an internal
+	// client.
+	InformerFor(obj runtime.Object, newFunc internalinterfaces.NewInformerFunc) cache.SharedIndexInformer
+
 	Samplecontroller() samplecontroller.Interface
 }