Changes to change system.

internal/notifier/notifier.go

@@ -0,0 +1,44 @@
+package notifier
+
+import (
+	"context"
+	"sync"
+)
+
+// A Notifier is a synchronization primitive for waking upp all listeners at once.
+type Notifier struct {
+	mutex sync.Mutex
+	ch    chan struct{}
+}
+
+// Broadcast wakes all listeners if there are any.
+func (notifier *Notifier) Broadcast() {
+	notifier.mutex.Lock()
+	if notifier.ch != nil {
+		close(notifier.ch)
+		notifier.ch = nil
+	}
+	notifier.mutex.Unlock()
+}
+
+// C gets the channel that'll close on the next notification.
+func (notifier *Notifier) C() <-chan struct{} {
+	notifier.mutex.Lock()
+	if notifier.ch == nil {
+		notifier.ch = make(chan struct{})
+	}
+	ch := notifier.ch
+	notifier.mutex.Unlock()
+
+	return ch
+}
+
+// Wait waits for the next `Broadcast` call, or the context's termination.
+func (notifier *Notifier) Wait(ctx context.Context) error {
+	select {
+	case <-notifier.C():
+		return nil
+	case <-ctx.Done():
+		return ctx.Err()
+	}
+}