fix

internal/conf/runtime.go

@@ -1,6 +1,7 @@
 package conf
 
 import (
+	"sync"
 	"sync/atomic"
 
 	"google.golang.org/protobuf/proto"
@@ -9,7 +10,10 @@ import (
 // Runtime owns the active immutable configuration snapshot. Callers always
 // receive clones so a config file reload cannot race with request handling.
 type Runtime struct {
-	snapshot atomic.Pointer[runtimeSnapshot]
+	snapshot  atomic.Pointer[runtimeSnapshot]
+	mu        sync.RWMutex
+	nextID    uint64
+	listeners map[uint64]func(*Data, *AdminBackend)
 }
 
 type runtimeSnapshot struct {
@@ -18,7 +22,7 @@ type runtimeSnapshot struct {
 }
 
 func NewRuntime(data *Data, admin *AdminBackend) *Runtime {
-	runtime := &Runtime{}
+	runtime := &Runtime{listeners: make(map[uint64]func(*Data, *AdminBackend))}
 	runtime.Replace(data, admin)
 	return runtime
 }
@@ -38,7 +42,37 @@ func cloneAdmin(value *AdminBackend) *AdminBackend {
 }
 
 func (r *Runtime) Replace(data *Data, admin *AdminBackend) {
-	r.snapshot.Store(&runtimeSnapshot{data: cloneData(data), admin: cloneAdmin(admin)})
+	data = cloneData(data)
+	admin = cloneAdmin(admin)
+	r.snapshot.Store(&runtimeSnapshot{data: data, admin: admin})
+	r.mu.RLock()
+	listeners := make([]func(*Data, *AdminBackend), 0, len(r.listeners))
+	for _, listener := range r.listeners {
+		listeners = append(listeners, listener)
+	}
+	r.mu.RUnlock()
+	for _, listener := range listeners {
+		listener(cloneData(data), cloneAdmin(admin))
+	}
+}
+
+// Subscribe registers a callback invoked after every successful runtime
+// configuration replacement. It is used by long-lived clients such as the
+// logger and other long-lived clients that must follow runtime config changes.
+func (r *Runtime) Subscribe(listener func(*Data, *AdminBackend)) func() {
+	if listener == nil {
+		return func() {}
+	}
+	r.mu.Lock()
+	r.nextID++
+	id := r.nextID
+	r.listeners[id] = listener
+	r.mu.Unlock()
+	return func() {
+		r.mu.Lock()
+		delete(r.listeners, id)
+		r.mu.Unlock()
+	}
 }
 
 func (r *Runtime) Data() *Data {