lib/ui: introduce Invalidatable

Many Drawable implementations have their own Invalidate and OnInvalidate
functions, with an unexported onInvalidate field. However OnInvalidate and
Invalidate are usually not called in the same goroutine. This results in a race
on this field, e.g.:

    Read at 0x00c000094748 by goroutine 7:
      git.sr.ht/~sircmpwn/aerc2/widgets.NewDirectoryList.func1()
          /home/simon/src/aerc2/widgets/dirlist.go:85 +0x56
      git.sr.ht/~sircmpwn/aerc2/widgets.(*Spinner).Start.func1()
          /home/simon/src/aerc2/widgets/spinner.go:93 +0x1bb

    Previous write at 0x00c000094748 by main goroutine:
      [failed to restore the stack]

    Goroutine 7 (running) created at:
      git.sr.ht/~sircmpwn/aerc2/widgets.(*Spinner).Start()
          /home/simon/src/aerc2/widgets/spinner.go:46 +0x8f
      git.sr.ht/~sircmpwn/aerc2/widgets.NewDirectoryList()
          /home/simon/src/aerc2/widgets/dirlist.go:37 +0x286
      git.sr.ht/~sircmpwn/aerc2/widgets.NewAccountView()
          /home/simon/src/aerc2/widgets/account.go:50 +0x5ca
      git.sr.ht/~sircmpwn/aerc2/widgets.NewAerc()
          /home/simon/src/aerc2/widgets/aerc.go:60 +0x800
      main.main()
          /home/simon/src/aerc2/aerc.go:65 +0x33e

To fix this, introduce a new type, Invalidatable, which protects the field.
Unfortunately the Drawable must be passed to the callback function in
Invalidate, so we still need to re-implement this in each Invalidatable user.

lib/ui/borders.go

@@ -12,6 +12,7 @@ const (
 )
 
 type Bordered struct {
+	Invalidatable
 	borders      uint
 	content      Drawable
 	onInvalidate func(d Drawable)
@@ -35,13 +36,7 @@ func (bordered *Bordered) Children() []Drawable {
 }
 
 func (bordered *Bordered) Invalidate() {
-	if bordered.onInvalidate != nil {
+	bordered.DoInvalidate(bordered)
-		bordered.onInvalidate(bordered)
-	}
-}
-
-func (bordered *Bordered) OnInvalidate(onInvalidate func(d Drawable)) {
-	bordered.onInvalidate = onInvalidate
 }
 
 func (bordered *Bordered) Draw(ctx *Context) {

lib/ui/grid.go

@@ -6,12 +6,12 @@ import (
 )
 
 type Grid struct {
+	Invalidatable
 	rows         []GridSpec
 	rowLayout    []gridLayout
 	columns      []GridSpec
 	columnLayout []gridLayout
 	cells        []*GridCell
-	onInvalidate func(d Drawable)
 	invalid      bool
 }
 
@@ -141,9 +141,7 @@ func (grid *Grid) reflow(ctx *Context) {
 
 func (grid *Grid) invalidateLayout() {
 	grid.invalid = true
-	if grid.onInvalidate != nil {
+	grid.DoInvalidate(grid)
-		grid.onInvalidate(grid)
-	}
 }
 
 func (grid *Grid) Invalidate() {
@@ -153,10 +151,6 @@ func (grid *Grid) Invalidate() {
 	}
 }
 
-func (grid *Grid) OnInvalidate(onInvalidate func(d Drawable)) {
-	grid.onInvalidate = onInvalidate
-}
-
 func (grid *Grid) AddChild(content Drawable) *GridCell {
 	cell := &GridCell{
 		RowSpan: 1,
@@ -193,7 +187,5 @@ func (grid *Grid) cellInvalidated(drawable Drawable) {
 		panic(fmt.Errorf("Attempted to invalidate unknown cell"))
 	}
 	cell.invalid = true
-	if grid.onInvalidate != nil {
+	grid.DoInvalidate(grid)
-		grid.onInvalidate(grid)
-	}
 }

lib/ui/invalidatable.go

@@ -0,0 +1,24 @@
+package ui
+
+import (
+	"sync/atomic"
+)
+
+type Invalidatable struct {
+	onInvalidate atomic.Value
+}
+
+func (i *Invalidatable) OnInvalidate(f func(d Drawable)) {
+	i.onInvalidate.Store(f)
+}
+
+func (i *Invalidatable) DoInvalidate(d Drawable) {
+	v := i.onInvalidate.Load()
+	if v == nil {
+		return
+	}
+	f := v.(func(d Drawable))
+	if f != nil {
+		f(d)
+	}
+}

lib/ui/text.go

@@ -12,13 +12,13 @@ const (
 )
 
 type Text struct {
+	Invalidatable
 	text     string
 	strategy uint
 	fg       tcell.Color
 	bg       tcell.Color
 	bold     bool
 	reverse  bool
-	onInvalidate func(d Drawable)
 }
 
 func NewText(text string) *Text {
@@ -80,12 +80,6 @@ func (t *Text) Draw(ctx *Context) {
 	ctx.Printf(x, 0, style, t.text)
 }
 
-func (t *Text) OnInvalidate(onInvalidate func(d Drawable)) {
-	t.onInvalidate = onInvalidate
-}
-
 func (t *Text) Invalidate() {
-	if t.onInvalidate != nil {
+	t.DoInvalidate(t)
-		t.onInvalidate(t)
-	}
 }

widgets/account.go

@@ -20,7 +20,6 @@ type AccountView struct {
 	grid      *ui.Grid
 	host      TabHost
 	logger    *log.Logger
-	onInvalidate func(d ui.Drawable)
 	msglist   *MessageList
 	msgStores map[string]*lib.MessageStore
 	worker    *types.Worker

widgets/dirlist.go

@@ -12,10 +12,10 @@ import (
 )
 
 type DirectoryList struct {
+	ui.Invalidatable
 	conf         *config.AccountConfig
 	dirs         []string
 	logger       *log.Logger
-	onInvalidate func(d ui.Drawable)
 	selecting    string
 	selected     string
 	spinner      *Spinner
@@ -77,14 +77,8 @@ func (dirlist *DirectoryList) Selected() string {
 	return dirlist.selected
 }
 
-func (dirlist *DirectoryList) OnInvalidate(onInvalidate func(d ui.Drawable)) {
-	dirlist.onInvalidate = onInvalidate
-}
-
 func (dirlist *DirectoryList) Invalidate() {
-	if dirlist.onInvalidate != nil {
+	dirlist.DoInvalidate(dirlist)
-		dirlist.onInvalidate(dirlist)
-	}
 }
 
 func (dirlist *DirectoryList) Draw(ctx *ui.Context) {

widgets/exline.go

@@ -12,6 +12,7 @@ import (
 // TODO: scrolling
 
 type ExLine struct {
+	ui.Invalidatable
 	command []rune
 	commit  func(cmd string)
 	ctx     *ui.Context
@@ -33,14 +34,8 @@ func NewExLine(commit func(cmd string), cancel func()) *ExLine {
 	}
 }
 
-func (ex *ExLine) OnInvalidate(onInvalidate func(d ui.Drawable)) {
-	ex.onInvalidate = onInvalidate
-}
-
 func (ex *ExLine) Invalidate() {
-	if ex.onInvalidate != nil {
+	ex.DoInvalidate(ex)
-		ex.onInvalidate(ex)
-	}
 }
 
 func (ex *ExLine) Draw(ctx *ui.Context) {

widgets/msglist.go

@@ -12,10 +12,10 @@ import (
 )
 
 type MessageList struct {
+	ui.Invalidatable
 	conf     *config.AercConfig
 	logger   *log.Logger
 	height   int
-	onInvalidate func(d ui.Drawable)
 	scroll   int
 	selected int
 	spinner  *Spinner
@@ -37,14 +37,8 @@ func NewMessageList(logger *log.Logger) *MessageList {
 	return ml
 }
 
-func (ml *MessageList) OnInvalidate(onInvalidate func(d ui.Drawable)) {
-	ml.onInvalidate = onInvalidate
-}
-
 func (ml *MessageList) Invalidate() {
-	if ml.onInvalidate != nil {
+	ml.DoInvalidate(ml)
-		ml.onInvalidate(ml)
-	}
 }
 
 func (ml *MessageList) Draw(ctx *ui.Context) {

widgets/msgviewer.go

@@ -252,8 +252,7 @@ func (mv *MessageViewer) Focus(focus bool) {
 }
 
 type HeaderView struct {
-	onInvalidate func(d ui.Drawable)
+	ui.Invalidatable
-
 	Name  string
 	Value string
 }
@@ -281,17 +280,11 @@ func (hv *HeaderView) Draw(ctx *ui.Context) {
 }
 
 func (hv *HeaderView) Invalidate() {
-	if hv.onInvalidate != nil {
+	hv.DoInvalidate(hv)
-		hv.onInvalidate(hv)
-	}
-}
-
-func (hv *HeaderView) OnInvalidate(fn func(d ui.Drawable)) {
-	hv.onInvalidate = fn
 }
 
 type MultipartView struct {
-	onInvalidate func(d ui.Drawable)
+	ui.Invalidatable
 }
 
 func (mpv *MultipartView) Draw(ctx *ui.Context) {
@@ -303,11 +296,5 @@ func (mpv *MultipartView) Draw(ctx *ui.Context) {
 }
 
 func (mpv *MultipartView) Invalidate() {
-	if mpv.onInvalidate != nil {
+	mpv.DoInvalidate(mpv)
-		mpv.onInvalidate(mpv)
-	}
-}
-
-func (mpv *MultipartView) OnInvalidate(fn func(d ui.Drawable)) {
-	mpv.onInvalidate = fn
 }

widgets/spinner.go

@@ -23,8 +23,8 @@ var (
 )
 
 type Spinner struct {
+	ui.Invalidatable
 	frame        int64 // access via atomic
-	onInvalidate func(d ui.Drawable)
 	stop         chan struct{}
 }
 
@@ -84,12 +84,6 @@ func (s *Spinner) Draw(ctx *ui.Context) {
 	ctx.Printf(col, 0, tcell.StyleDefault, "%s", frames[cur])
 }
 
-func (s *Spinner) OnInvalidate(onInvalidate func(d ui.Drawable)) {
-	s.onInvalidate = onInvalidate
-}
-
 func (s *Spinner) Invalidate() {
-	if s.onInvalidate != nil {
+	s.DoInvalidate(s)
-		s.onInvalidate(s)
-	}
 }

widgets/status.go

@@ -9,10 +9,9 @@ import (
 )
 
 type StatusLine struct {
+	ui.Invalidatable
 	stack    []*StatusMessage
 	fallback StatusMessage
-
-	onInvalidate func(d ui.Drawable)
 }
 
 type StatusMessage struct {
@@ -31,14 +30,8 @@ func NewStatusLine() *StatusLine {
 	}
 }
 
-func (status *StatusLine) OnInvalidate(onInvalidate func(d ui.Drawable)) {
-	status.onInvalidate = onInvalidate
-}
-
 func (status *StatusLine) Invalidate() {
-	if status.onInvalidate != nil {
+	status.DoInvalidate(status)
-		status.onInvalidate(status)
-	}
 }
 
 func (status *StatusLine) Draw(ctx *ui.Context) {

widgets/terminal.go

@@ -88,6 +88,7 @@ func init() {
 }
 
 type Terminal struct {
+	ui.Invalidatable
 	closed      bool
 	cmd         *exec.Cmd
 	colors      map[tcell.Color]tcell.Color
@@ -98,7 +99,6 @@ type Terminal struct {
 	destroyed   bool
 	err         error
 	focus       bool
-	onInvalidate func(d ui.Drawable)
 	pty         *os.File
 	start       chan interface{}
 	vterm       *vterm.VTerm
@@ -225,10 +225,6 @@ func (term *Terminal) Destroy() {
 	term.destroyed = true
 }
 
-func (term *Terminal) OnInvalidate(cb func(d ui.Drawable)) {
-	term.onInvalidate = cb
-}
-
 func (term *Terminal) Invalidate() {
 	if term.vterm != nil {
 		width, height := term.vterm.Size()
@@ -239,9 +235,7 @@ func (term *Terminal) Invalidate() {
 }
 
 func (term *Terminal) invalidate() {
-	if term.onInvalidate != nil {
+	term.DoInvalidate(term)
-		term.onInvalidate(term)
-	}
 }
 
 func (term *Terminal) Draw(ctx *ui.Context) {