Use simpler implementation without Context for notifier.

notifier.go

@@ -29,7 +29,11 @@ import (
 type Waiter struct {
 	key string
 
-	SingleWaiter
+	sw *SingleWaiter
+}
+
+func (w *Waiter) Wait(ctx context.Context) error {
+	return w.sw.Wait(ctx)
 }
 
 type Notifier struct {
@@ -47,22 +51,15 @@ func (n *Notifier) NewWaiter(key string) *Waiter {
 	if found {
 		w := &Waiter{
 			key: key,
-			SingleWaiter: SingleWaiter{
-				ctx:    waiter.ctx,
-				cancel: waiter.cancel,
-			},
+			sw:  waiter.sw,
 		}
 		n.waiterMap[key][w] = true
 		return w
 	}
 
-	ctx, cancel := context.WithCancel(context.Background())
 	waiter = &Waiter{
 		key: key,
-		SingleWaiter: SingleWaiter{
-			ctx:    ctx,
-			cancel: cancel,
-		},
+		sw:  newSingleWaiter(),
 	}
 	if n.waiters == nil {
 		n.waiters = make(map[string]*Waiter)
@@ -83,7 +80,7 @@ func (n *Notifier) Reset() {
 	defer n.Unlock()
 
 	for _, w := range n.waiters {
-		w.cancel()
+		w.sw.cancel()
 	}
 	n.waiters = nil
 	n.waiterMap = nil
@@ -98,7 +95,7 @@ func (n *Notifier) Release(w *Waiter) {
 			delete(waiters, w)
 			if len(waiters) == 0 {
 				delete(n.waiters, w.key)
-				w.cancel()
+				w.sw.cancel()
 			}
 		}
 	}
@@ -109,7 +106,7 @@ func (n *Notifier) Notify(key string) {
 	defer n.Unlock()
 
 	if w, found := n.waiters[key]; found {
-		w.cancel()
+		w.sw.cancel()
 		delete(n.waiters, w.key)
 		delete(n.waiterMap, w.key)
 	}

single_notifier.go

@@ -27,19 +27,43 @@ import (
 )
 
 type SingleWaiter struct {
-	ctx    context.Context
-	cancel context.CancelFunc
+	root bool
+	ch   chan struct{}
+	once sync.Once
+}
+
+func newSingleWaiter() *SingleWaiter {
+	return &SingleWaiter{
+		root: true,
+		ch:   make(chan struct{}),
+	}
+}
+
+func (w *SingleWaiter) subWaiter() *SingleWaiter {
+	return &SingleWaiter{
+		ch: w.ch,
+	}
 }
 
 func (w *SingleWaiter) Wait(ctx context.Context) error {
 	select {
-	case <-w.ctx.Done():
+	case <-w.ch:
 		return nil
 	case <-ctx.Done():
 		return ctx.Err()
 	}
 }
 
+func (w *SingleWaiter) cancel() {
+	if !w.root {
+		return
+	}
+
+	w.once.Do(func() {
+		close(w.ch)
+	})
+}
+
 type SingleNotifier struct {
 	sync.Mutex
 
@@ -52,21 +76,14 @@ func (n *SingleNotifier) NewWaiter() *SingleWaiter {
 	defer n.Unlock()
 
 	if n.waiter == nil {
-		ctx, cancel := context.WithCancel(context.Background())
-		n.waiter = &SingleWaiter{
-			ctx:    ctx,
-			cancel: cancel,
-		}
+		n.waiter = newSingleWaiter()
 	}
 
 	if n.waiters == nil {
 		n.waiters = make(map[*SingleWaiter]bool)
 	}
 
-	w := &SingleWaiter{
-		ctx:    n.waiter.ctx,
-		cancel: n.waiter.cancel,
-	}
+	w := n.waiter.subWaiter()
 	n.waiters[w] = true
 	return w
 }