ui/app: (macOS) serialize access to the views map

The CVDisplayLink used for synchronizing rendering to the display
refresh rate runs on a separate thread from the main thread.
View callbacks must therefore be serialized. Implement that by
introducing a singleton goroutine that owns the view map and runs
incoming commands.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

ui/app/os_macos.go

@@ -15,6 +15,7 @@ import (
 	"errors"
 	"image"
 	"runtime"
+	"sync"
 	"time"
 	"unsafe"
 
@@ -34,11 +35,43 @@ type window struct {
 	stage Stage
 }
 
+type viewCmd struct {
+	view C.CFTypeRef
+	f    viewFunc
+}
+
+type viewFunc func(views viewMap, view C.CFTypeRef)
+
+type viewMap map[C.CFTypeRef]*window
+
+var (
+	viewOnce sync.Once
+	viewCmds = make(chan viewCmd)
+	viewAcks = make(chan struct{})
+)
+
 var mainWindow = newWindowRendezvous()
 
 var viewFactory func() C.CFTypeRef
 
-var views = make(map[C.CFTypeRef]*window)
+func viewDo(view C.CFTypeRef, f viewFunc) {
+	viewOnce.Do(func() {
+		go runViewCmdLoop()
+	})
+	viewCmds <- viewCmd{view, f}
+	<-viewAcks
+}
+
+func runViewCmdLoop() {
+	views := make(viewMap)
+	for {
+		select {
+		case cmd := <-viewCmds:
+			cmd.f(views, cmd.view)
+			viewAcks <- struct{}{}
+		}
+	}
+}
 
 func (w *window) contextView() C.CFTypeRef {
 	return w.view
@@ -62,12 +95,18 @@ func (w *window) setStage(stage Stage) {
 	w.w.event(StageEvent{stage})
 }
 
-//export gio_onFrameCallback
+// Use a top level func for onFrameCallback to avoid
-func gio_onFrameCallback(view C.CFTypeRef) {
+// garbage from viewDo.
+func onFrameCmd(views viewMap, view C.CFTypeRef) {
 	w := views[view]
 	w.draw(false)
 }
 
+//export gio_onFrameCallback
+func gio_onFrameCallback(view C.CFTypeRef) {
+	viewDo(view, onFrameCmd)
+}
+
 //export gio_onKeys
 func gio_onKeys(view C.CFTypeRef, cstr *C.char, ti C.double, mods C.NSUInteger) {
 	str := C.GoString(cstr)
@@ -78,19 +117,23 @@ func gio_onKeys(view C.CFTypeRef, cstr *C.char, ti C.double, mods C.NSUInteger)
 	if mods&C.NSEventModifierFlagShift != 0 {
 		kmods |= key.ModShift
 	}
+	viewDo(view, func(views viewMap, view C.CFTypeRef) {
 		w := views[view]
 		for _, k := range str {
 			if n, ok := convertKey(k); ok {
 				w.w.event(key.ChordEvent{Name: n, Modifiers: kmods})
 			}
 		}
+	})
 }
 
 //export gio_onText
 func gio_onText(view C.CFTypeRef, cstr *C.char) {
 	str := C.GoString(cstr)
+	viewDo(view, func(views viewMap, view C.CFTypeRef) {
 		w := views[view]
 		w.w.event(key.EditEvent{Text: str})
+	})
 }
 
 //export gio_onMouse
@@ -107,6 +150,7 @@ func gio_onMouse(view C.CFTypeRef, cdir C.int, x, y, dx, dy C.CGFloat, ti C.doub
 		panic("invalid direction")
 	}
 	t := time.Duration(float64(ti)*float64(time.Second) + .5)
+	viewDo(view, func(views viewMap, view C.CFTypeRef) {
 		w := views[view]
 		w.w.event(pointer.Event{
 			Type:     typ,
@@ -115,18 +159,23 @@ func gio_onMouse(view C.CFTypeRef, cdir C.int, x, y, dx, dy C.CGFloat, ti C.doub
 			Position: f32.Point{X: float32(x), Y: float32(y)},
 			Scroll:   f32.Point{X: float32(dx), Y: float32(dy)},
 		})
+	})
 }
 
 //export gio_onDraw
 func gio_onDraw(view C.CFTypeRef) {
+	viewDo(view, func(views viewMap, view C.CFTypeRef) {
 		w := views[view]
 		w.draw(true)
+	})
 }
 
 //export gio_onFocus
 func gio_onFocus(view C.CFTypeRef, focus C.BOOL) {
+	viewDo(view, func(views viewMap, view C.CFTypeRef) {
 		w := views[view]
 		w.w.event(key.FocusEvent{Focus: focus == C.YES})
+	})
 }
 
 func (w *window) draw(sync bool) {
@@ -161,25 +210,32 @@ func getConfig() Config {
 
 //export gio_onTerminate
 func gio_onTerminate(view C.CFTypeRef) {
+	viewDo(view, func(views viewMap, view C.CFTypeRef) {
 		w := views[view]
 		delete(views, view)
 		w.w.event(DestroyEvent{})
+	})
 }
 
 //export gio_onHide
 func gio_onHide(view C.CFTypeRef) {
+	viewDo(view, func(views viewMap, view C.CFTypeRef) {
 		w := views[view]
 		w.setStage(StagePaused)
+	})
 }
 
 //export gio_onShow
 func gio_onShow(view C.CFTypeRef) {
+	viewDo(view, func(views viewMap, view C.CFTypeRef) {
 		w := views[view]
 		w.setStage(StageRunning)
+	})
 }
 
 //export gio_onCreate
 func gio_onCreate(view C.CFTypeRef) {
+	viewDo(view, func(views viewMap, view C.CFTypeRef) {
 		w := &window{
 			view: view,
 		}
@@ -187,6 +243,7 @@ func gio_onCreate(view C.CFTypeRef) {
 		w.w = wopts.window
 		w.w.setDriver(w)
 		views[view] = w
+	})
 }
 
 func createWindow(win *Window, opts *WindowOptions) error {