apiserver/watchcache: doc watch event fan-out to blocked watchers better

Kubernetes-commit: 94b2bb1d3dcfe7973329cc56024f449adde4086c

pkg/storage/cacher/cacher.go

@@ -934,8 +934,11 @@ func (c *Cacher) dispatchEvent(event *watchCacheEvent) {
 			timeout := c.dispatchTimeoutBudget.takeAvailable()
 			c.timer.Reset(timeout)
 
-			// Make sure every watcher will try to send event without blocking first,
-			// even if the timer has already expired.
+			// Send event to all blocked watchers. As long as timer is running,
+			// `add` will wait for the watcher to unblock. After timeout,
+			// `add` will not wait, but immediately close a still blocked watcher.
+			// Hence, every watcher gets the chance to unblock itself while timer
+			// is running, not only the first ones in the list.
 			timer := c.timer
 			for _, watcher := range c.blockedWatchers {
 				if !watcher.add(event, timer) {