[#585] fstree: Add optional file counter

Signed-off-by: Dmitrii Stepanov <d.stepanov@yadro.com>

pkg/util/sync/key_locker_test.go

@@ -0,0 +1,32 @@
+package sync
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+	"golang.org/x/sync/errgroup"
+)
+
+func TestKeyLocker(t *testing.T) {
+	taken := false
+	eg, _ := errgroup.WithContext(context.Background())
+	keyLocker := NewKeyLocker[int]()
+	for i := 0; i < 100; i++ {
+		eg.Go(func() error {
+			keyLocker.Lock(0)
+			defer keyLocker.Unlock(0)
+
+			require.False(t, taken)
+			taken = true
+			require.True(t, taken)
+			time.Sleep(10 * time.Millisecond)
+			taken = false
+			require.False(t, taken)
+
+			return nil
+		})
+	}
+	require.NoError(t, eg.Wait())
+}