fix: race in Single.Do

common/singledo/singledo.go

@@ -13,25 +13,26 @@ type call[T any] struct {
 
 type Single[T any] struct {
 	mux    sync.Mutex
-	last   time.Time
 	wait   time.Duration
 	call   *call[T]
 	result *Result[T]
 }
 
 type Result[T any] struct {
-	Val T
-	Err error
+	Val  T
+	Err  error
+	Time time.Time
 }
 
 // Do single.Do likes sync.singleFlight
 func (s *Single[T]) Do(fn func() (T, error)) (v T, err error, shared bool) {
 	s.mux.Lock()
-	now := time.Now()
-	if now.Before(s.last.Add(s.wait)) {
+	result := s.result
+	if result != nil && time.Since(result.Time) < s.wait {
 		s.mux.Unlock()
-		return s.result.Val, s.result.Err, true
+		return result.Val, result.Err, true
 	}
+	s.result = nil // The result has expired, clear it
 
 	if callM := s.call; callM != nil {
 		s.mux.Unlock()
@@ -47,15 +48,19 @@ func (s *Single[T]) Do(fn func() (T, error)) (v T, err error, shared bool) {
 	callM.wg.Done()
 
 	s.mux.Lock()
-	s.call = nil
-	s.result = &Result[T]{callM.val, callM.err}
-	s.last = now
+	if s.call == callM { // maybe reset when fn is running
+		s.call = nil
+		s.result = &Result[T]{callM.val, callM.err, time.Now()}
+	}
 	s.mux.Unlock()
 	return callM.val, callM.err, false
 }
 
 func (s *Single[T]) Reset() {
-	s.last = time.Time{}
+	s.mux.Lock()
+	s.call = nil
+	s.result = nil
+	s.mux.Unlock()
 }
 
 func NewSingle[T any](wait time.Duration) *Single[T] {