Merge pull request #61195 from grantr/use-race-free-fake-watcher

Automatic merge from submit-queue (batch tested with PRs 61195, 61479). 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>.

Use RaceFreeFakeWatcher in ObjectTracker to fix racy watch panics

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

The `FakeWatcher` added to `ObjectTracker` in #57504 allows sends on the result channel after it's closed; for example calling `Stop()` then `Add(obj)` will cause a panic. In my experience this has led to flaky tests when informers and controllers are running.

Replacing `FakeWatcher` with `RaceFreeFakeWatcher` fixes the problem, since `RaceFreeFakeWatcher` ignores additional events that occur after the watcher is stopped. It also panics instead of blocking when the result channel is full, which seems like a more useful behavior in tests than blocking.

I removed the `FakeWatchBufferSize` constant since `RaceFreeFakeWatcher` doesn't take a buffer size argument anymore. This seems fine since the `DefaultChanSize` constant is close to the `FakeWatchBufferSize` value (100 vs 128).

**Special notes for your reviewer**:

I can provide a minimal repro of a flaky test caused by the earlier behavior if necessary.

**Release note**:
```release-note
Fix racy panics when using fake watches with ObjectTracker
```

staging/src/k8s.io/client-go/testing/fixture.go

@@ -29,11 +29,6 @@ import (
 	restclient "k8s.io/client-go/rest"
 )
 
-// FakeWatchBufferSize is the max num of watch event can be buffered in the
-// watch channel. Note that when watch event overflows or exceed this buffer
-// size, manipulations via fake client may be blocked.
-const FakeWatchBufferSize = 128
-
 // ObjectTracker keeps track of objects. It is intended to be used to
 // fake calls to a server by returning objects based on their kind,
 // namespace and name.
@@ -142,12 +137,11 @@ type tracker struct {
 	lock    sync.RWMutex
 	objects map[schema.GroupVersionResource][]runtime.Object
 	// The value type of watchers is a map of which the key is either a namespace or
-	// all/non namespace aka "" and its value is list of fake watchers. Each of
-	// fake watcher holds a buffered channel of size "FakeWatchBufferSize" which
-	// is default to 128. Manipulations on resources will broadcast the notification
-	// events into the watchers' channel and note that too many unhandled event may
-	// potentially block the tracker.
-	watchers map[schema.GroupVersionResource]map[string][]*watch.FakeWatcher
+	// all/non namespace aka "" and its value is list of fake watchers.
+	// Manipulations on resources will broadcast the notification events into the
+	// watchers' channel. Note that too many unhandled events (currently 100,
+	// see apimachinery/pkg/watch.DefaultChanSize) will cause a panic.
+	watchers map[schema.GroupVersionResource]map[string][]*watch.RaceFreeFakeWatcher
 }
 
 var _ ObjectTracker = &tracker{}
@@ -159,7 +153,7 @@ func NewObjectTracker(scheme ObjectScheme, decoder runtime.Decoder) ObjectTracke
 		scheme:   scheme,
 		decoder:  decoder,
 		objects:  make(map[schema.GroupVersionResource][]runtime.Object),
-		watchers: make(map[schema.GroupVersionResource]map[string][]*watch.FakeWatcher),
+		watchers: make(map[schema.GroupVersionResource]map[string][]*watch.RaceFreeFakeWatcher),
 	}
 }
 
@@ -206,10 +200,10 @@ func (t *tracker) Watch(gvr schema.GroupVersionResource, ns string) (watch.Inter
 	t.lock.Lock()
 	defer t.lock.Unlock()
 
-	fakewatcher := watch.NewFakeWithChanSize(FakeWatchBufferSize, true)
+	fakewatcher := watch.NewRaceFreeFake()
 
 	if _, exists := t.watchers[gvr]; !exists {
-		t.watchers[gvr] = make(map[string][]*watch.FakeWatcher)
+		t.watchers[gvr] = make(map[string][]*watch.RaceFreeFakeWatcher)
 	}
 	t.watchers[gvr][ns] = append(t.watchers[gvr][ns], fakewatcher)
 	return fakewatcher, nil
@@ -293,8 +287,8 @@ func (t *tracker) Update(gvr schema.GroupVersionResource, obj runtime.Object, ns
 	return t.add(gvr, obj, ns, true)
 }
 
-func (t *tracker) getWatches(gvr schema.GroupVersionResource, ns string) []*watch.FakeWatcher {
-	watches := []*watch.FakeWatcher{}
+func (t *tracker) getWatches(gvr schema.GroupVersionResource, ns string) []*watch.RaceFreeFakeWatcher {
+	watches := []*watch.RaceFreeFakeWatcher{}
 	if t.watchers[gvr] != nil {
 		if w := t.watchers[gvr][ns]; w != nil {
 			watches = append(watches, w...)

staging/src/k8s.io/client-go/testing/fixture_test.go

@@ -190,3 +190,34 @@ func TestWatchCallMultipleInvocation(t *testing.T) {
 	}
 	wg.Wait()
 }
+
+func TestWatchAddAfterStop(t *testing.T) {
+	testResource := schema.GroupVersionResource{Group: "", Version: "test_version", Resource: "test_kind"}
+	testObj := getArbitraryResource(testResource, "test_name", "test_namespace")
+	accessor, err := meta.Accessor(testObj)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	ns := accessor.GetNamespace()
+	scheme := runtime.NewScheme()
+	codecs := serializer.NewCodecFactory(scheme)
+	o := NewObjectTracker(scheme, codecs.UniversalDecoder())
+	watch, err := o.Watch(testResource, ns)
+	if err != nil {
+		t.Errorf("watch creation failed: %v", err)
+	}
+
+	// When the watch is stopped it should ignore later events without panicking.
+	defer func() {
+		if r := recover(); r != nil {
+			t.Errorf("Watch panicked when it should have ignored create after stop: %v", r)
+		}
+	}()
+
+	watch.Stop()
+	err = o.Create(testResource, testObj, ns)
+	if err != nil {
+		t.Errorf("test resource creation failed: %v", err)
+	}
+}