fix race + add test for detect race

Author: asmyasnikov

internal/pool/pool.go

@@ -66,31 +66,46 @@ func (s *safeStats) Get() stats.Stats {
 }
 
 func (s *safeStats) Index() statsItemAddr {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+
 	return statsItemAddr{
 		v: &s.v.Index,
 		onChange: func(f func()) {
 			s.mu.WithLock(f)
-			s.onChange(s.v)
+			if s.onChange != nil {
+				s.onChange(s.Get())
+			}
 		},
 	}
 }
 
 func (s *safeStats) Idle() statsItemAddr {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+
 	return statsItemAddr{
 		v: &s.v.Idle,
 		onChange: func(f func()) {
 			s.mu.WithLock(f)
-			s.onChange(s.v)
+			if s.onChange != nil {
+				s.onChange(s.Get())
+			}
 		},
 	}
 }
 
 func (s *safeStats) InUse() statsItemAddr {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+
 	return statsItemAddr{
 		v: &s.v.InUse,
 		onChange: func(f func()) {
 			s.mu.WithLock(f)
-			s.onChange(s.v)
+			if s.onChange != nil {
+				s.onChange(s.Get())
+			}
 		},
 	}
 }

internal/pool/pool_test.go

@@ -3,6 +3,7 @@ package pool
 import (
 	"context"
 	"errors"
+	"math/rand"
 	"sync"
 	"sync/atomic"
 	"testing"
@@ -289,3 +290,31 @@ func TestPool(t *testing.T) {
 		}, xtest.StopAfter(42*time.Second))
 	})
 }
+
+func TestSafeStatsRace(t *testing.T) {
+	xtest.TestManyTimes(t, func(t testing.TB) {
+		var (
+			wg sync.WaitGroup
+			s  = &safeStats{}
+		)
+		wg.Add(10000)
+		for range make([]struct{}, 10000) {
+			go func() {
+				defer wg.Done()
+				require.NotPanics(t, func() {
+					switch rand.Int31n(4) { //nolint:gosec
+					case 0:
+						s.Index().Inc()
+					case 1:
+						s.InUse().Inc()
+					case 2:
+						s.Idle().Inc()
+					default:
+						s.Get()
+					}
+				})
+			}()
+		}
+		wg.Wait()
+	}, xtest.StopAfter(5*time.Second))
+}