Merge pull request moby#4004 from alexcb/acb/sampler-data-race-fix

sampler data race fix

Author: tonistiigi

executor/resources/sampler.go

@@ -10,7 +10,7 @@ type WithTimestamp interface {
 }
 
 type Sampler[T WithTimestamp] struct {
-	mu          sync.RWMutex
+	mu          sync.Mutex
 	minInterval time.Duration
 	maxSamples  int
 	callback    func(ts time.Time) (T, error)
@@ -32,9 +32,9 @@ type Sub[T WithTimestamp] struct {
 func (s *Sub[T]) Close(captureLast bool) ([]T, error) {
 	s.sampler.mu.Lock()
 	delete(s.sampler.subs, s)
-	s.sampler.mu.Unlock()
 
 	if s.err != nil {
+		s.sampler.mu.Unlock()
 		return nil, s.err
 	}
 	current := s.first
@@ -46,6 +46,7 @@ func (s *Sub[T]) Close(captureLast bool) ([]T, error) {
 			current = ts
 		}
 	}
+	s.sampler.mu.Unlock()
 
 	if captureLast {
 		v, err := s.sampler.callback(time.Now())
@@ -94,22 +95,26 @@ func (s *Sampler[T]) run() {
 			return
 		case <-ticker.C:
 			tm := time.Now()
+			s.mu.Lock()
 			active := make([]*Sub[T], 0, len(s.subs))
-			s.mu.RLock()
 			for ss := range s.subs {
 				if tm.Sub(ss.last) < ss.interval {
 					continue
 				}
 				ss.last = tm
 				active = append(active, ss)
 			}
-			s.mu.RUnlock()
+			s.mu.Unlock()
 			ticker = time.NewTimer(s.minInterval)
 			if len(active) == 0 {
 				continue
 			}
 			value, err := s.callback(tm)
+			s.mu.Lock()
 			for _, ss := range active {
+				if _, found := s.subs[ss]; !found {
+					continue // skip if Close() was called while the lock was released
+				}
 				if err != nil {
 					ss.err = err
 				} else {
@@ -121,6 +126,7 @@ func (s *Sampler[T]) run() {
 					ss.interval *= 2
 				}
 			}
+			s.mu.Unlock()
 		}
 	}
 }