Better waiting for watch event delivery in cacher

pkg/storage/cacher.go

@@ -532,17 +532,23 @@ func (c *Cacher) dispatchEvents() {
 func (c *Cacher) dispatchEvent(event *watchCacheEvent) {
 	triggerValues, supported := c.triggerValues(event)
 
+	// TODO: For now we assume we have a given <timeout> budget for dispatching
+	// a single event. We should consider changing to the approach with:
+	// - budget has upper bound at <max_timeout>
+	// - we add <portion> to current timeout every second
+	timeout := time.Duration(250) * time.Millisecond
+
 	c.Lock()
 	defer c.Unlock()
 	// Iterate over "allWatchers" no matter what the trigger function is.
 	for _, watcher := range c.watchers.allWatchers {
-		watcher.add(event)
+		watcher.add(event, &timeout)
 	}
 	if supported {
 		// Iterate over watchers interested in the given values of the trigger.
 		for _, triggerValue := range triggerValues {
 			for _, watcher := range c.watchers.valueWatchers[triggerValue] {
-				watcher.add(event)
+				watcher.add(event, &timeout)
 			}
 		}
 	} else {
@@ -555,7 +561,7 @@ func (c *Cacher) dispatchEvent(event *watchCacheEvent) {
 		// Iterate over watchers interested in exact values for all values.
 		for _, watchers := range c.watchers.valueWatchers {
 			for _, watcher := range watchers {
-				watcher.add(event)
+				watcher.add(event, &timeout)
 			}
 		}
 	}
@@ -729,7 +735,7 @@ func (c *cacheWatcher) stop() {
 
 var timerPool sync.Pool
 
-func (c *cacheWatcher) add(event *watchCacheEvent) {
+func (c *cacheWatcher) add(event *watchCacheEvent, timeout *time.Duration) {
 	// Try to send the event immediately, without blocking.
 	select {
 	case c.input <- *event:
@@ -737,20 +743,16 @@ func (c *cacheWatcher) add(event *watchCacheEvent) {
 	default:
 	}
 
-	// OK, block sending, but only for up to 5 seconds.
+	// OK, block sending, but only for up to <timeout>.
 	// cacheWatcher.add is called very often, so arrange
 	// to reuse timers instead of constantly allocating.
-	trace := util.NewTrace(
-		fmt.Sprintf("cacheWatcher %v: waiting for add (initial result size %v)",
-			reflect.TypeOf(event.Object).String(), len(c.result)))
-	defer trace.LogIfLong(50 * time.Millisecond)
+	startTime := time.Now()
 
-	const timeout = 5 * time.Second
 	t, ok := timerPool.Get().(*time.Timer)
 	if ok {
-		t.Reset(timeout)
+		t.Reset(*timeout)
 	} else {
-		t = time.NewTimer(timeout)
+		t = time.NewTimer(*timeout)
 	}
 	defer timerPool.Put(t)
 
@@ -769,6 +771,10 @@ func (c *cacheWatcher) add(event *watchCacheEvent) {
 		c.forget(false)
 		c.stop()
 	}
+
+	if *timeout = *timeout - time.Since(startTime); *timeout < 0 {
+		*timeout = 0
+	}
 }
 
 // NOTE: sendWatchCacheEvent is assumed to not modify <event> !!!

pkg/storage/cacher_test.go

@@ -297,12 +297,15 @@ func TestWatcherTimeout(t *testing.T) {
 	}
 	startVersion := strconv.Itoa(int(initialVersion))
 
-	// Create a watcher that will not be reading any result.
-	watcher, err := cacher.WatchList(context.TODO(), "pods/ns", startVersion, storage.Everything)
-	if err != nil {
-		t.Fatalf("Unexpected error: %v", err)
+	// Create a number of watchers that will not be reading any result.
+	nonReadingWatchers := 50
+	for i := 0; i < nonReadingWatchers; i++ {
+		watcher, err := cacher.WatchList(context.TODO(), "pods/ns", startVersion, storage.Everything)
+		if err != nil {
+			t.Fatalf("Unexpected error: %v", err)
+		}
+		defer watcher.Stop()
 	}
-	defer watcher.Stop()
 
 	// Create a second watcher that will be reading result.
 	readingWatcher, err := cacher.WatchList(context.TODO(), "pods/ns", startVersion, storage.Everything)
@@ -311,11 +314,15 @@ func TestWatcherTimeout(t *testing.T) {
 	}
 	defer readingWatcher.Stop()
 
+	startTime := time.Now()
 	for i := 1; i <= 22; i++ {
 		pod := makeTestPod(strconv.Itoa(i))
 		_ = updatePod(t, etcdStorage, pod, nil)
 		verifyWatchEvent(t, readingWatcher, watch.Added, pod)
 	}
+	if time.Since(startTime) > time.Duration(250*nonReadingWatchers)*time.Millisecond {
+		t.Errorf("waiting for events took too long: %v", time.Since(startTime))
+	}
 }
 
 func TestFiltering(t *testing.T) {