policy: lazily start SelectorCache.handleUserNotifications

Hive wants components to not start any goroutines during startup.
Change SelectorCache so that handleUserNotifications is started
when the first notification is queued, not when SelectorCache is
created.

Signed-off-by: Lorenz Bauer <lmb@isovalent.com>

daemon/cmd/cells_test.go

@@ -22,7 +22,6 @@ var goleakOptions = []goleak.Option{
 	// Ignore goroutines started by the policy trifecta, see [newPolicyTrifecta].
 	goleak.IgnoreTopFunction("github.com/cilium/cilium/pkg/identity/cache.(*identityWatcher).watch.func1"),
 	goleak.IgnoreTopFunction("github.com/cilium/cilium/pkg/trigger.(*Trigger).waiter"),
-	goleak.IgnoreTopFunction("sync.runtime_notifyListWait"),
 }
 
 // TestAgentCell verifies that the Agent hive can be instantiated with

pkg/policy/selectorcache.go

@@ -221,6 +221,9 @@ type SelectorCache struct {
 	userMutex lock.Mutex
 	// userNotes holds a FIFO list of user notifications to be made
 	userNotes []userNotification
+
+	// used to lazily start the handler for user notifications.
+	startNotificationsHandlerOnce sync.Once
 }
 
 // GetModel returns the API model of the SelectorCache.
@@ -267,6 +270,9 @@ func (sc *SelectorCache) handleUserNotifications() {
 }
 
 func (sc *SelectorCache) queueUserNotification(user CachedSelectionUser, selector CachedSelector, added, deleted []identity.NumericIdentity, wg *sync.WaitGroup) {
+	sc.startNotificationsHandlerOnce.Do(func() {
+		go sc.handleUserNotifications()
+	})
 	wg.Add(1)
 	sc.userMutex.Lock()
 	sc.userNotes = append(sc.userNotes, userNotification{
@@ -288,8 +294,6 @@ func NewSelectorCache(allocator cache.IdentityAllocator, ids cache.IdentityCache
 		selectors:   make(map[string]identitySelector),
 	}
 	sc.userCond = sync.NewCond(&sc.userMutex)
-	go sc.handleUserNotifications()
-
 	return sc
 }