layer1: add namespace manager subscribers step 9

pkg/utils/namespace_manager.go

@@ -6,10 +6,16 @@ import (
 	"time"
 )
 
+type NamespaceSubscriber interface {
+	Name() string
+}
+
 type NamespaceManager interface {
 	Snapshot() []string
 	SnapshotRecords() []NamespaceRecord
 	Get(name string) (NamespaceRecord, bool)
+	Subscribe(subscriber NamespaceSubscriber)
+	SnapshotSubscribers() []string
 	Upsert(event NamespaceEvent) NamespaceRecord
 	MarkPartState(namespace string, part string, state NamespacePartState) (NamespaceRecord, bool)
 	Remove(name string) bool
@@ -18,14 +24,34 @@ type NamespaceManager interface {
 type inMemoryNamespaceManager struct {
 	mu      sync.RWMutex
 	records map[string]NamespaceRecord
+	subs    map[string]NamespaceSubscriber
 }
 
 func NewNamespaceManager() NamespaceManager {
 	return &inMemoryNamespaceManager{
 		records: make(map[string]NamespaceRecord),
+		subs:    make(map[string]NamespaceSubscriber),
 	}
 }
 
+func (m *inMemoryNamespaceManager) Subscribe(subscriber NamespaceSubscriber) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	m.subs[subscriber.Name()] = subscriber
+}
+
+func (m *inMemoryNamespaceManager) SnapshotSubscribers() []string {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+
+	names := make([]string, 0, len(m.subs))
+	for name := range m.subs {
+		names = append(names, name)
+	}
+	sort.Strings(names)
+	return names
+}
+
 func (m *inMemoryNamespaceManager) Snapshot() []string {
 	m.mu.RLock()
 	defer m.mu.RUnlock()