all: Transactionalize db.FileSet (fixes #5952) (#6239)

lib/model/folder.go

@@ -328,11 +328,16 @@ func (f *folder) scanSubdirs(subDirs []string) error {
 		subDirs[i] = sub
 	}
 
+	snap := f.fset.Snapshot()
+	// We release explicitly later in this function, however we might exit early
+	// and it's ok to release twice.
+	defer snap.Release()
+
 	// Clean the list of subitems to ensure that we start at a known
 	// directory, and don't scan subdirectories of things we've already
 	// scanned.
 	subDirs = unifySubs(subDirs, func(file string) bool {
-		_, ok := f.fset.Get(protocol.LocalDeviceID, file)
+		_, ok := snap.Get(protocol.LocalDeviceID, file)
 		return ok
 	})
 
@@ -344,7 +349,7 @@ func (f *folder) scanSubdirs(subDirs []string) error {
 		Subs:                  subDirs,
 		Matcher:               f.ignores,
 		TempLifetime:          time.Duration(f.model.cfg.Options().KeepTemporariesH) * time.Hour,
-		CurrentFiler:          cFiler{f.fset},
+		CurrentFiler:          cFiler{snap},
 		Filesystem:            mtimefs,
 		IgnorePerms:           f.IgnorePerms,
 		AutoNormalize:         f.AutoNormalize,
@@ -369,7 +374,7 @@ func (f *folder) scanSubdirs(subDirs []string) error {
 		oldBatchFn := batchFn // can't reference batchFn directly (recursion)
 		batchFn = func(fs []protocol.FileInfo) error {
 			for i := range fs {
-				switch gf, ok := f.fset.GetGlobal(fs[i].Name); {
+				switch gf, ok := snap.GetGlobal(fs[i].Name); {
 				case !ok:
 					continue
 				case gf.IsEquivalentOptional(fs[i], f.ModTimeWindow(), false, false, protocol.FlagLocalReceiveOnly):
@@ -426,10 +431,15 @@ func (f *folder) scanSubdirs(subDirs []string) error {
 	// ignored files.
 	var toIgnore []db.FileInfoTruncated
 	ignoredParent := ""
+
+	snap.Release()
+	snap = f.fset.Snapshot()
+	defer snap.Release()
+
 	for _, sub := range subDirs {
 		var iterError error
 
-		f.fset.WithPrefixedHaveTruncated(protocol.LocalDeviceID, sub, func(fi db.FileIntf) bool {
+		snap.WithPrefixedHaveTruncated(protocol.LocalDeviceID, sub, func(fi db.FileIntf) bool {
 			select {
 			case <-f.ctx.Done():
 				return false
@@ -891,7 +901,7 @@ func unifySubs(dirs []string, exists func(dir string) bool) []string {
 }
 
 type cFiler struct {
-	*db.FileSet
+	*db.Snapshot
 }
 
 // Implements scanner.CurrentFiler