Harden backup and restore operations

internal/queue/queue.go

@@ -25,10 +25,12 @@ type Queue struct {
 	stopping bool
 	handler  Handler
 	onChange OnChange
+	done     chan struct{}
+	doneOnce sync.Once
 }
 
 func New(handler Handler, onChange OnChange) *Queue {
-	q := &Queue{handler: handler, onChange: onChange}
+	q := &Queue{handler: handler, onChange: onChange, done: make(chan struct{})}
 	q.cond = sync.NewCond(&q.mu)
 	return q
 }
@@ -71,6 +73,7 @@ func (q *Queue) Enqueue(run model.Run) error {
 }
 
 func (q *Queue) Run(ctx context.Context) {
+	defer q.doneOnce.Do(func() { close(q.done) })
 	for {
 		q.mu.Lock()
 		for len(q.pending) == 0 && !q.stopping {
@@ -104,6 +107,15 @@ func (q *Queue) Run(ctx context.Context) {
 	}
 }
 
+func (q *Queue) Wait(ctx context.Context) error {
+	select {
+	case <-q.done:
+		return nil
+	case <-ctx.Done():
+		return ctx.Err()
+	}
+}
+
 func (q *Queue) Cancel(id string) bool {
 	q.mu.Lock()
 	defer q.mu.Unlock()