client-go informers: context-aware Start + WaitForCacheSync

Passing a context to StartWithContext enables context-aware reflector
logging. This is the main remaining source of log spam (output to stderr
instead of per-test logger) in controller unit tests.

WaitForCacheSynceWithContext takes advantage of the new cache.WaitFor +
NamedHasSynced functionality to finish "immediately" (= no virtual time
passed) in a synctest bubble. While at it, the return type gets improved so
that a failure is easier to handle.

Kubernetes-commit: 5ff323de791df88880f6e065f5de4b445e5c90ed

pkg/generated/informers/externalversions/factory.go

@@ -19,6 +19,7 @@ limitations under the License.
 package externalversions
 
 import (
+	context "context"
 	reflect "reflect"
 	sync "sync"
 	time "time"
@@ -26,6 +27,7 @@ import (
 	v1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	runtime "k8s.io/apimachinery/pkg/runtime"
 	schema "k8s.io/apimachinery/pkg/runtime/schema"
+	wait "k8s.io/apimachinery/pkg/util/wait"
 	cache "k8s.io/client-go/tools/cache"
 	versioned "k8s.io/sample-controller/pkg/generated/clientset/versioned"
 	internalinterfaces "k8s.io/sample-controller/pkg/generated/informers/externalversions/internalinterfaces"
@@ -139,6 +141,10 @@ func NewSharedInformerFactoryWithOptions(client versioned.Interface, defaultResy
 }
 
 func (f *sharedInformerFactory) Start(stopCh <-chan struct{}) {
+	f.StartWithContext(wait.ContextForChannel(stopCh))
+}
+
+func (f *sharedInformerFactory) StartWithContext(ctx context.Context) {
 	f.lock.Lock()
 	defer f.lock.Unlock()
 
@@ -148,15 +154,9 @@ func (f *sharedInformerFactory) Start(stopCh <-chan struct{}) {
 
 	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.wg.Go(func() {
+				informer.RunWithContext(ctx)
+			})
 			f.startedInformers[informerType] = true
 		}
 	}
@@ -173,6 +173,11 @@ func (f *sharedInformerFactory) Shutdown() {
 }
 
 func (f *sharedInformerFactory) WaitForCacheSync(stopCh <-chan struct{}) map[reflect.Type]bool {
+	result := f.WaitForCacheSyncWithContext(wait.ContextForChannel(stopCh))
+	return result.Synced
+}
+
+func (f *sharedInformerFactory) WaitForCacheSyncWithContext(ctx context.Context) cache.SyncResult {
 	informers := func() map[reflect.Type]cache.SharedIndexInformer {
 		f.lock.Lock()
 		defer f.lock.Unlock()
@@ -186,10 +191,31 @@ func (f *sharedInformerFactory) WaitForCacheSync(stopCh <-chan struct{}) map[ref
 		return informers
 	}()
 
-	res := map[reflect.Type]bool{}
-	for informType, informer := range informers {
-		res[informType] = cache.WaitForCacheSync(stopCh, informer.HasSynced)
+	// Wait for informers to sync, without polling.
+	cacheSyncs := make([]cache.DoneChecker, 0, len(informers))
+	for _, informer := range informers {
+		cacheSyncs = append(cacheSyncs, informer.HasSyncedChecker())
 	}
+	cache.WaitFor(ctx, "" /* no logging */, cacheSyncs...)
+
+	res := cache.SyncResult{
+		Synced: make(map[reflect.Type]bool, len(informers)),
+	}
+	failed := false
+	for informType, informer := range informers {
+		hasSynced := informer.HasSynced()
+		if !hasSynced {
+			failed = true
+		}
+		res.Synced[informType] = hasSynced
+	}
+	if failed {
+		// context.Cause is more informative than ctx.Err().
+		// This must be non-nil, otherwise WaitFor wouldn't have stopped
+		// prematurely.
+		res.Err = context.Cause(ctx)
+	}
+
 	return res
 }
 
@@ -228,27 +254,46 @@ func (f *sharedInformerFactory) InformerFor(obj runtime.Object, newFunc internal
 //	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
-//	    }
+//	handle, err := typeInformer.Informer().AddEventHandler(...)
+//	if err != nil {
+//	    return fmt.Errorf("register event handler: %v", err)
+//	}
+//	defer typeInformer.Informer().RemoveEventHandler(handle) // Avoids leaking goroutines.
+//	factory.StartWithContext(ctx)                            // Start processing these informers.
+//	synced := factory.WaitForCacheSyncWithContext(ctx)
+//	if err := synced.AsError(); err != nil {
+//	    return err
+//	}
+//	for v := range synced {
+//	    // Only if desired log some information similar to this.
+//	    fmt.Fprintf(os.Stdout, "cache synced: %s", v)
+//	}
+//
+//	// Also make sure that all of the initial cache events have been delivered.
+//	if !WaitFor(ctx, "event handler sync", handle.HasSyncedChecker()) {
+//	    // Must have failed because of context.
+//	    return fmt.Errorf("sync event handler: %w", context.Cause(ctx))
 //	}
 //
 //	// Creating informers can also be created after Start, but then
 //	// Start must be called again:
 //	anotherGenericInformer := factory.ForResource(resource)
-//	factory.Start(ctx.Done())
+//	factory.StartWithContext(ctx)
 type SharedInformerFactory interface {
 	internalinterfaces.SharedInformerFactory
 
 	// Start initializes all requested informers. They are handled in goroutines
 	// which run until the stop channel gets closed.
 	// Warning: Start does not block. When run in a go-routine, it will race with a later WaitForCacheSync.
+	//
+	// Contextual logging: StartWithContext should be used instead of Start in code which supports contextual logging.
 	Start(stopCh <-chan struct{})
 
+	// StartWithContext initializes all requested informers. They are handled in goroutines
+	// which run until the context gets canceled.
+	// Warning: StartWithContext does not block. When run in a go-routine, it will race with a later WaitForCacheSync.
+	StartWithContext(ctx context.Context)
+
 	// Shutdown marks a factory as shutting down. At that point no new
 	// informers can be started anymore and Start will return without
 	// doing anything.
@@ -263,8 +308,14 @@ type SharedInformerFactory interface {
 
 	// WaitForCacheSync blocks until all started informers' caches were synced
 	// or the stop channel gets closed.
+	//
+	// Contextual logging: WaitForCacheSync should be used instead of WaitForCacheSync in code which supports contextual logging. It also returns a more useful result.
 	WaitForCacheSync(stopCh <-chan struct{}) map[reflect.Type]bool
 
+	// WaitForCacheSyncWithContext blocks until all started informers' caches were synced
+	// or the context gets canceled.
+	WaitForCacheSyncWithContext(ctx context.Context) cache.SyncResult
+
 	// ForResource gives generic access to a shared informer of the matching type.
 	ForResource(resource schema.GroupVersionResource) (GenericInformer, error)