app,app/internal/wm: introduce app.Window.Run and use it internally

app.Window implements a method for safely running functions against the
underlying native window through the driverFuncs channel. However, the
functions still run in a different goroutine than the one driving the
native event loop, which forces the implementations in package wm to do
complicated synchronization.

A previous change added a mechanism to run functions in the native event
loop thread. The macOS port needed this functionality, but with some
care it can be generalized. That's what this change does through the
new Run method.

The advantage is that the thread switch dance is now confined to
app.Window, with the help of a generic wm.Driver.Wakeup method. All
other Driver methods can then assume they run on their event loop
threads.

Run is exported because it is also needed for programs that use
Windows configured with CustomRenderer to control their own rendering.

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

app/internal/wm/d3d11_windows.go

@@ -72,7 +72,10 @@ func (c *d3d11Context) Present() error {
 }
 
 func (c *d3d11Context) MakeCurrent() error {
-	_, width, height := c.win.HWND()
+	var width, height int
+	c.win.w.Run(func() {
+		_, width, height = c.win.HWND()
+	})
 	if c.renderTarget != nil && width == c.width && height == c.height {
 		c.ctx.OMSetRenderTargets(c.renderTarget, c.depthView)
 		return nil

app/internal/wm/egl_android.go

@@ -3,6 +3,7 @@
 package wm
 
 /*
+#include <android/native_window_jni.h>
 #include <EGL/egl.h>
 */
 import "C"
@@ -35,7 +36,15 @@ func (c *context) Release() {
 
 func (c *context) MakeCurrent() error {
 	c.Context.ReleaseSurface()
-	win, width, height := c.win.nativeWindow(c.Context.VisualID())
+	var (
+		win           *C.ANativeWindow
+		width, height int
+	)
+	// Run on main thread. Deadlock is avoided because MakeCurrent is only
+	// called during a FrameEvent.
+	c.win.callbacks.Run(func() {
+		win, width, height = c.win.nativeWindow(c.Context.VisualID())
+	})
 	if win == nil {
 		return nil
 	}

app/internal/wm/egl_windows.go

@@ -3,6 +3,8 @@
 package wm
 
 import (
+	"golang.org/x/sys/windows"
+
 	"gioui.org/internal/egl"
 )
 
@@ -34,7 +36,13 @@ func (c *glContext) Release() {
 
 func (c *glContext) MakeCurrent() error {
 	c.Context.ReleaseSurface()
-	win, width, height := c.win.HWND()
+	var (
+		win           windows.Handle
+		width, height int
+	)
+	c.win.w.Run(func() {
+		win, width, height = c.win.HWND()
+	})
 	eglSurf := egl.NativeWindowType(win)
 	if err := c.Context.CreateSurface(eglSurf, width, height); err != nil {
 		return err

app/internal/wm/gl_macos.go

@@ -43,7 +43,7 @@ func newContext(w *window) (*context, error) {
 	}
 	// [NSOpenGLContext setView] must run on the main thread. Fortunately,
 	// newContext is only called during a [NSView draw] on the main thread.
-	w.w.Func(func() {
+	w.w.Run(func() {
 		C.gio_setContextView(ctx, view)
 	})
 	c := &context{

app/internal/wm/os_android.go

@@ -42,7 +42,6 @@ import "C"
 import (
 	"errors"
 	"fmt"
-	"gioui.org/internal/f32color"
 	"image"
 	"image/color"
 	"reflect"
@@ -53,6 +52,8 @@ import (
 	"unicode/utf16"
 	"unsafe"
 
+	"gioui.org/internal/f32color"
+
 	"gioui.org/f32"
 	"gioui.org/io/clipboard"
 	"gioui.org/io/key"
@@ -70,24 +71,11 @@ type window struct {
 	fontScale float32
 	insets    system.Insets
 
-	stage   system.Stage
-	started bool
-
-	state, newState windowState
-
-	// mu protects the fields following it.
-	mu        sync.Mutex
-	win       *C.ANativeWindow
+	stage     system.Stage
+	started   bool
 	animating bool
-}
 
-// windowState tracks the View or Activity specific state lost when Android
-// re-creates our Activity.
-type windowState struct {
-	cursor          *pointer.CursorName
-	orientation     *Orientation
-	navigationColor *color.NRGBA
-	statusColor     *color.NRGBA
+	win *C.ANativeWindow
 }
 
 // gioView hold cached JNI methods for GioView.
@@ -247,7 +235,6 @@ func Java_org_gioui_GioView_onCreateView(env *C.JNIEnv, class C.jclass, view C.j
 	views[handle] = w
 	w.loadConfig(env, class)
 	w.Option(wopts.opts)
-	applyStateDiff(env, view, windowState{}, w.state)
 	w.setStage(system.StagePaused)
 	w.callbacks.Event(ViewEvent{View: uintptr(view)})
 	return handle
@@ -274,7 +261,7 @@ func Java_org_gioui_GioView_onStopView(env *C.JNIEnv, class C.jclass, handle C.j
 func Java_org_gioui_GioView_onStartView(env *C.JNIEnv, class C.jclass, handle C.jlong) {
 	w := views[handle]
 	w.started = true
-	if w.aNativeWindow() != nil {
+	if w.win != nil {
 		w.setVisible()
 	}
 }
@@ -282,18 +269,14 @@ func Java_org_gioui_GioView_onStartView(env *C.JNIEnv, class C.jclass, handle C.
 //export Java_org_gioui_GioView_onSurfaceDestroyed
 func Java_org_gioui_GioView_onSurfaceDestroyed(env *C.JNIEnv, class C.jclass, handle C.jlong) {
 	w := views[handle]
-	w.mu.Lock()
 	w.win = nil
-	w.mu.Unlock()
 	w.setStage(system.StagePaused)
 }
 
 //export Java_org_gioui_GioView_onSurfaceChanged
 func Java_org_gioui_GioView_onSurfaceChanged(env *C.JNIEnv, class C.jclass, handle C.jlong, surf C.jobject) {
 	w := views[handle]
-	w.mu.Lock()
 	w.win = C.ANativeWindow_fromSurface(env, surf)
-	w.mu.Unlock()
 	if w.started {
 		w.setVisible()
 	}
@@ -323,9 +306,7 @@ func Java_org_gioui_GioView_onFrameCallback(env *C.JNIEnv, class C.jclass, view
 	if w.stage < system.StageRunning {
 		return
 	}
-	w.mu.Lock()
 	anim := w.animating
-	w.mu.Unlock()
 	if anim {
 		runInJVM(javaVM(), func(env *C.JNIEnv) {
 			callVoidMethod(env, w.view, gioView.postFrameCallback)
@@ -348,7 +329,7 @@ func Java_org_gioui_GioView_onBack(env *C.JNIEnv, class C.jclass, view C.jlong)
 //export Java_org_gioui_GioView_onFocusChange
 func Java_org_gioui_GioView_onFocusChange(env *C.JNIEnv, class C.jclass, view C.jlong, focus C.jboolean) {
 	w := views[view]
-	w.callbacks.Event(key.FocusEvent{Focus: focus == C.JNI_TRUE})
+	go w.callbacks.Event(key.FocusEvent{Focus: focus == C.JNI_TRUE})
 }
 
 //export Java_org_gioui_GioView_onWindowInsets
@@ -366,8 +347,7 @@ func Java_org_gioui_GioView_onWindowInsets(env *C.JNIEnv, class C.jclass, view C
 }
 
 func (w *window) setVisible() {
-	win := w.aNativeWindow()
-	width, height := C.ANativeWindow_getWidth(win), C.ANativeWindow_getHeight(win)
+	width, height := C.ANativeWindow_getWidth(w.win), C.ANativeWindow_getHeight(w.win)
 	if width == 0 || height == 0 {
 		return
 	}
@@ -384,22 +364,15 @@ func (w *window) setStage(stage system.Stage) {
 }
 
 func (w *window) nativeWindow(visID int) (*C.ANativeWindow, int, int) {
-	win := w.aNativeWindow()
 	var width, height int
-	if win != nil {
-		if C.ANativeWindow_setBuffersGeometry(win, 0, 0, C.int32_t(visID)) != 0 {
+	if w.win != nil {
+		if C.ANativeWindow_setBuffersGeometry(w.win, 0, 0, C.int32_t(visID)) != 0 {
 			panic(errors.New("ANativeWindow_setBuffersGeometry failed"))
 		}
-		w, h := C.ANativeWindow_getWidth(win), C.ANativeWindow_getHeight(win)
+		w, h := C.ANativeWindow_getWidth(w.win), C.ANativeWindow_getHeight(w.win)
 		width, height = int(w), int(h)
 	}
-	return win, width, height
-}
-
-func (w *window) aNativeWindow() *C.ANativeWindow {
-	w.mu.Lock()
-	defer w.mu.Unlock()
-	return w.win
+	return w.win, width, height
 }
 
 func (w *window) loadConfig(env *C.JNIEnv, class C.jclass) {
@@ -417,23 +390,16 @@ func (w *window) loadConfig(env *C.JNIEnv, class C.jclass) {
 }
 
 func (w *window) SetAnimating(anim bool) {
-	w.mu.Lock()
 	w.animating = anim
-	w.mu.Unlock()
 	if anim {
-		runOnMain(func(env *C.JNIEnv) {
-			if w.view == 0 {
-				// View was destroyed while switching to main thread.
-				return
-			}
+		runInJVM(javaVM(), func(env *C.JNIEnv) {
 			callVoidMethod(env, w.view, gioView.postFrameCallback)
 		})
 	}
 }
 
 func (w *window) draw(sync bool) {
-	win := w.aNativeWindow()
-	width, height := C.ANativeWindow_getWidth(win), C.ANativeWindow_getHeight(win)
+	width, height := C.ANativeWindow_getWidth(w.win), C.ANativeWindow_getHeight(w.win)
 	if width == 0 || height == 0 {
 		return
 	}
@@ -567,10 +533,7 @@ func Java_org_gioui_GioView_onTouchEvent(env *C.JNIEnv, class C.jclass, handle C
 }
 
 func (w *window) ShowTextInput(show bool) {
-	runOnMain(func(env *C.JNIEnv) {
-		if w.view == 0 {
-			return
-		}
+	runInJVM(javaVM(), func(env *C.JNIEnv) {
 		if show {
 			callVoidMethod(env, w.view, gioView.showTextInput)
 		} else {
@@ -669,7 +632,7 @@ func NewWindow(window Callbacks, opts *Options) error {
 }
 
 func (w *window) WriteClipboard(s string) {
-	runOnMain(func(env *C.JNIEnv) {
+	runInJVM(javaVM(), func(env *C.JNIEnv) {
 		jstr := javaString(env, s)
 		callStaticVoidMethod(env, android.gioCls, android.mwriteClipboard,
 			jvalue(android.appCtx), jvalue(jstr))
@@ -677,71 +640,43 @@ func (w *window) WriteClipboard(s string) {
 }
 
 func (w *window) ReadClipboard() {
-	runOnMain(func(env *C.JNIEnv) {
+	runInJVM(javaVM(), func(env *C.JNIEnv) {
 		c, err := callStaticObjectMethod(env, android.gioCls, android.mreadClipboard,
 			jvalue(android.appCtx))
 		if err != nil {
 			return
 		}
 		content := goString(env, C.jstring(c))
-		w.callbacks.Event(clipboard.Event{Text: content})
+		go w.callbacks.Event(clipboard.Event{Text: content})
 	})
 }
 
 func (w *window) Option(opts *Options) {
-	if o := opts.Orientation; o != nil {
-		w.setState(func(state *windowState) {
-			state.orientation = o
-		})
-	}
-	if o := opts.NavigationColor; o != nil {
-		w.setState(func(state *windowState) {
-			state.navigationColor = o
-		})
-	}
-	if o := opts.StatusColor; o != nil {
-		w.setState(func(state *windowState) {
-			state.statusColor = o
-		})
-	}
+	runInJVM(javaVM(), func(env *C.JNIEnv) {
+		if o := opts.Orientation; o != nil {
+			setOrientation(env, w.view, *o)
+		}
+		if o := opts.NavigationColor; o != nil {
+			setNavigationColor(env, w.view, *o)
+		}
+		if o := opts.StatusColor; o != nil {
+			setStatusColor(env, w.view, *o)
+		}
+	})
 }
 
 func (w *window) SetCursor(name pointer.CursorName) {
-	w.setState(func(state *windowState) {
-		state.cursor = &name
+	runInJVM(javaVM(), func(env *C.JNIEnv) {
+		setCursor(env, w.view, name)
 	})
 }
 
-// setState adjust the window state on the main thread.
-func (w *window) setState(f func(state *windowState)) {
+func (w *window) Wakeup() {
 	runOnMain(func(env *C.JNIEnv) {
-		f(&w.newState)
-		if w.view == 0 {
-			// No View attached. The state will be applied at next onCreateView.
-			return
-		}
-		old := w.state
-		state := w.newState
-		applyStateDiff(env, w.view, old, state)
-		w.state = state
+		w.callbacks.Event(WakeupEvent{})
 	})
 }
 
-func applyStateDiff(env *C.JNIEnv, view C.jobject, old, state windowState) {
-	if state.cursor != nil && old.cursor != state.cursor {
-		setCursor(env, view, *state.cursor)
-	}
-	if state.orientation != nil && old.orientation != state.orientation {
-		setOrientation(env, view, *state.orientation)
-	}
-	if state.navigationColor != nil && old.navigationColor != state.navigationColor {
-		setNavigationColor(env, view, *state.navigationColor)
-	}
-	if state.statusColor != nil && old.statusColor != state.statusColor {
-		setStatusColor(env, view, *state.statusColor)
-	}
-}
-
 func setCursor(env *C.JNIEnv, view C.jobject, name pointer.CursorName) {
 	var curID int
 	switch name {

app/internal/wm/os_darwin.go

@@ -222,3 +222,9 @@ func windowSetCursor(from, to pointer.CursorName) pointer.CursorName {
 	})
 	return to
 }
+
+func (w *window) Wakeup() {
+	runOnMain(func() {
+		w.w.Event(WakeupEvent{})
+	})
+}

app/internal/wm/os_ios.go

@@ -224,21 +224,17 @@ func onTouch(last C.int, view, touchRef C.CFTypeRef, phase C.NSInteger, x, y C.C
 }
 
 func (w *window) ReadClipboard() {
-	runOnMain(func() {
-		content := nsstringToString(C.gio_readClipboard())
-		w.w.Event(clipboard.Event{Text: content})
-	})
+	content := nsstringToString(C.gio_readClipboard())
+	go w.w.Event(clipboard.Event{Text: content})
 }
 
 func (w *window) WriteClipboard(s string) {
 	u16 := utf16.Encode([]rune(s))
-	runOnMain(func() {
-		var chars *C.unichar
-		if len(u16) > 0 {
-			chars = (*C.unichar)(unsafe.Pointer(&u16[0]))
-		}
-		C.gio_writeClipboard(chars, C.NSUInteger(len(u16)))
-	})
+	var chars *C.unichar
+	if len(u16) > 0 {
+		chars = (*C.unichar)(unsafe.Pointer(&u16[0]))
+	}
+	C.gio_writeClipboard(chars, C.NSUInteger(len(u16)))
 }
 
 func (w *window) Option(opts *Options) {}
@@ -294,19 +290,11 @@ func (w *window) isVisible() bool {
 }
 
 func (w *window) ShowTextInput(show bool) {
-	v := w.view
-	if v == 0 {
-		return
+	if show {
+		C.gio_showTextInput(w.view)
+	} else {
+		C.gio_hideTextInput(w.view)
 	}
-	C.CFRetain(v)
-	runOnMain(func() {
-		defer C.CFRelease(v)
-		if show {
-			C.gio_showTextInput(w.view)
-		} else {
-			C.gio_hideTextInput(w.view)
-		}
-	})
 }
 
 // Close the window. Not implemented for iOS.

app/internal/wm/os_js.go

@@ -7,7 +7,6 @@ import (
 	"image"
 	"image/color"
 	"strings"
-	"sync"
 	"syscall/js"
 	"time"
 	"unicode"
@@ -47,7 +46,6 @@ type window struct {
 	chanAnimation chan struct{}
 	chanRedraw    chan struct{}
 
-	mu        sync.Mutex
 	size      f32.Point
 	inset     f32.Point
 	scale     float32
@@ -55,6 +53,7 @@ type window struct {
 	// animRequested tracks whether a requestAnimationFrame callback
 	// is pending.
 	animRequested bool
+	wakeups       chan struct{}
 }
 
 func NewWindow(win Callbacks, opts *Options) error {
@@ -71,6 +70,7 @@ func NewWindow(win Callbacks, opts *Options) error {
 		window:    js.Global().Get("window"),
 		head:      doc.Get("head"),
 		clipboard: js.Global().Get("navigator").Get("clipboard"),
+		wakeups:   make(chan struct{}, 1),
 	}
 	w.requestAnimationFrame = w.window.Get("requestAnimationFrame")
 	w.browserHistory = w.window.Get("history")
@@ -89,7 +89,7 @@ func NewWindow(win Callbacks, opts *Options) error {
 	})
 	w.clipboardCallback = w.funcOf(func(this js.Value, args []js.Value) interface{} {
 		content := args[0].String()
-		win.Event(clipboard.Event{Text: content})
+		go win.Event(clipboard.Event{Text: content})
 		return nil
 	})
 	w.addEventListeners()
@@ -106,6 +106,8 @@ func NewWindow(win Callbacks, opts *Options) error {
 		w.draw(true)
 		for {
 			select {
+			case <-w.wakeups:
+				w.w.Event(WakeupEvent{})
 			case <-w.chanAnimation:
 				w.animCallback()
 			case <-w.chanRedraw:
@@ -349,9 +351,7 @@ func (w *window) touchEvent(typ pointer.Type, e js.Value) {
 	changedTouches := e.Get("changedTouches")
 	n := changedTouches.Length()
 	rect := w.cnv.Call("getBoundingClientRect")
-	w.mu.Lock()
 	scale := w.scale
-	w.mu.Unlock()
 	var mods key.Modifiers
 	if e.Get("shiftKey").Bool() {
 		mods |= key.ModShift
@@ -401,9 +401,7 @@ func (w *window) pointerEvent(typ pointer.Type, dx, dy float32, e js.Value) {
 	rect := w.cnv.Call("getBoundingClientRect")
 	x -= rect.Get("left").Float()
 	y -= rect.Get("top").Float()
-	w.mu.Lock()
 	scale := w.scale
-	w.mu.Unlock()
 	pos := f32.Point{
 		X: float32(x) * scale,
 		Y: float32(y) * scale,
@@ -452,21 +450,17 @@ func (w *window) funcOf(f func(this js.Value, args []js.Value) interface{}) js.F
 }
 
 func (w *window) animCallback() {
-	w.mu.Lock()
 	anim := w.animating
 	w.animRequested = anim
 	if anim {
 		w.requestAnimationFrame.Invoke(w.redraw)
 	}
-	w.mu.Unlock()
 	if anim {
 		w.draw(false)
 	}
 }
 
 func (w *window) SetAnimating(anim bool) {
-	w.mu.Lock()
-	defer w.mu.Unlock()
 	w.animating = anim
 	if anim && !w.animRequested {
 		w.animRequested = true
@@ -511,6 +505,13 @@ func (w *window) SetCursor(name pointer.CursorName) {
 	style.Set("cursor", string(name))
 }
 
+func (w *window) Wakeup() {
+	select {
+	case w.wakeups <- struct{}{}:
+	default:
+	}
+}
+
 func (w *window) ShowTextInput(show bool) {
 	// Run in a goroutine to avoid a deadlock if the
 	// focus change result in an event.
@@ -527,9 +528,6 @@ func (w *window) ShowTextInput(show bool) {
 func (w *window) Close() {}
 
 func (w *window) resize() {
-	w.mu.Lock()
-	defer w.mu.Unlock()
-
 	w.scale = float32(w.window.Get("devicePixelRatio").Float())
 
 	rect := w.cnv.Call("getBoundingClientRect")
@@ -570,9 +568,6 @@ func (w *window) draw(sync bool) {
 }
 
 func (w *window) config() (int, int, system.Insets, unit.Metric) {
-	w.mu.Lock()
-	defer w.mu.Unlock()
-
 	return int(w.size.X + .5), int(w.size.Y + .5), system.Insets{
 			Bottom: unit.Px(w.inset.Y),
 			Right:  unit.Px(w.inset.X),

app/internal/wm/os_macos.go

@@ -122,60 +122,54 @@ func (w *window) contextView() C.CFTypeRef {
 }
 
 func (w *window) ReadClipboard() {
-	runOnMain(func() {
-		content := nsstringToString(C.gio_readClipboard())
-		w.w.Event(clipboard.Event{Text: content})
-	})
+	content := nsstringToString(C.gio_readClipboard())
+	go w.w.Event(clipboard.Event{Text: content})
 }
 
 func (w *window) WriteClipboard(s string) {
 	u16 := utf16.Encode([]rune(s))
-	runOnMain(func() {
-		var chars *C.unichar
-		if len(u16) > 0 {
-			chars = (*C.unichar)(unsafe.Pointer(&u16[0]))
-		}
-		C.gio_writeClipboard(chars, C.NSUInteger(len(u16)))
-	})
+	var chars *C.unichar
+	if len(u16) > 0 {
+		chars = (*C.unichar)(unsafe.Pointer(&u16[0]))
+	}
+	C.gio_writeClipboard(chars, C.NSUInteger(len(u16)))
 }
 
 func (w *window) Option(opts *Options) {
-	w.runOnMain(func() {
-		screenScale := float32(C.gio_getScreenBackingScale())
-		cfg := configFor(screenScale)
-		val := func(v unit.Value) float32 {
-			return float32(cfg.Px(v)) / screenScale
+	screenScale := float32(C.gio_getScreenBackingScale())
+	cfg := configFor(screenScale)
+	val := func(v unit.Value) float32 {
+		return float32(cfg.Px(v)) / screenScale
+	}
+	if o := opts.Size; o != nil {
+		width := val(o.Width)
+		height := val(o.Height)
+		if width > 0 || height > 0 {
+			C.gio_setSize(w.window, C.CGFloat(width), C.CGFloat(height))
 		}
-		if o := opts.Size; o != nil {
-			width := val(o.Width)
-			height := val(o.Height)
-			if width > 0 || height > 0 {
-				C.gio_setSize(w.window, C.CGFloat(width), C.CGFloat(height))
-			}
+	}
+	if o := opts.MinSize; o != nil {
+		width := val(o.Width)
+		height := val(o.Height)
+		if width > 0 || height > 0 {
+			C.gio_setMinSize(w.window, C.CGFloat(width), C.CGFloat(height))
 		}
-		if o := opts.MinSize; o != nil {
-			width := val(o.Width)
-			height := val(o.Height)
-			if width > 0 || height > 0 {
-				C.gio_setMinSize(w.window, C.CGFloat(width), C.CGFloat(height))
-			}
+	}
+	if o := opts.MaxSize; o != nil {
+		width := val(o.Width)
+		height := val(o.Height)
+		if width > 0 || height > 0 {
+			C.gio_setMaxSize(w.window, C.CGFloat(width), C.CGFloat(height))
 		}
-		if o := opts.MaxSize; o != nil {
-			width := val(o.Width)
-			height := val(o.Height)
-			if width > 0 || height > 0 {
-				C.gio_setMaxSize(w.window, C.CGFloat(width), C.CGFloat(height))
-			}
-		}
-		if o := opts.Title; o != nil {
-			title := C.CString(*o)
-			defer C.free(unsafe.Pointer(title))
-			C.gio_setTitle(w.window, title)
-		}
-		if o := opts.WindowMode; o != nil {
-			w.SetWindowMode(*o)
-		}
-	})
+	}
+	if o := opts.Title; o != nil {
+		title := C.CString(*o)
+		defer C.free(unsafe.Pointer(title))
+		C.gio_setTitle(w.window, title)
+	}
+	if o := opts.WindowMode; o != nil {
+		w.SetWindowMode(*o)
+	}
 }
 
 func (w *window) SetWindowMode(mode WindowMode) {
@@ -212,9 +206,7 @@ func (w *window) runOnMain(f func()) {
 }
 
 func (w *window) Close() {
-	w.runOnMain(func() {
-		C.gio_close(w.window)
-	})
+	C.gio_close(w.window)
 }
 
 func (w *window) setStage(stage system.Stage) {

app/internal/wm/os_wayland.go

@@ -179,9 +179,7 @@ type window struct {
 	dead              bool
 	lastFrameCallback *C.struct_wl_callback
 
-	mu        sync.Mutex
 	animating bool
-	opts      *Options
 	needAck   bool
 	// The most recent configure serial waiting to be ack'ed.
 	serial   C.uint32_t
@@ -189,10 +187,8 @@ type window struct {
 	height   int
 	newScale bool
 	scale    int
-	// readClipboard tracks whether a ClipboardEvent is requested.
-	readClipboard bool
-	// writeClipboard is set whenever a clipboard write is requested.
-	writeClipboard *string
+
+	wakeups chan struct{}
 }
 
 type poller struct {
@@ -319,6 +315,7 @@ func (d *wlDisplay) createNativeWindow(opts *Options) (*window, error) {
 		newScale: scale != 1,
 		ppdp:     ppdp,
 		ppsp:     ppdp,
+		wakeups:  make(chan struct{}, 1),
 	}
 	w.surf = C.wl_compositor_create_surface(d.compositor)
 	if w.surf == nil {
@@ -473,10 +470,8 @@ func gio_onSeatName(data unsafe.Pointer, seat *C.struct_wl_seat, name *C.char) {
 //export gio_onXdgSurfaceConfigure
 func gio_onXdgSurfaceConfigure(data unsafe.Pointer, wmSurf *C.struct_xdg_surface, serial C.uint32_t) {
 	w := callbackLoad(data).(*window)
-	w.mu.Lock()
 	w.serial = serial
 	w.needAck = true
-	w.mu.Unlock()
 	w.setStage(system.StageRunning)
 	w.draw(true)
 }
@@ -491,8 +486,6 @@ func gio_onToplevelClose(data unsafe.Pointer, topLvl *C.struct_xdg_toplevel) {
 func gio_onToplevelConfigure(data unsafe.Pointer, topLvl *C.struct_xdg_toplevel, width, height C.int32_t, states *C.struct_wl_array) {
 	w := callbackLoad(data).(*window)
 	if width != 0 && height != 0 {
-		w.mu.Lock()
-		defer w.mu.Unlock()
 		w.width = int(width)
 		w.height = int(height)
 		w.updateOpaqueRegion()
@@ -868,8 +861,6 @@ func (w *window) flushFling() {
 	invDist := 1 / vel
 	w.fling.dir.X = estx.Velocity * invDist
 	w.fling.dir.Y = esty.Velocity * invDist
-	// Wake up the window loop.
-	w.disp.wakeup()
 }
 
 //export gio_onPointerAxisSource
@@ -897,24 +888,26 @@ func gio_onPointerAxisDiscrete(data unsafe.Pointer, p *C.struct_wl_pointer, axis
 }
 
 func (w *window) ReadClipboard() {
-	w.mu.Lock()
-	w.readClipboard = true
-	w.mu.Unlock()
-	w.disp.wakeup()
+	r, err := w.disp.readClipboard()
+	// Send empty responses on unavailable clipboards or errors.
+	if r == nil || err != nil {
+		w.w.Event(clipboard.Event{})
+		return
+	}
+	// Don't let slow clipboard transfers block event loop.
+	go func() {
+		defer r.Close()
+		data, _ := ioutil.ReadAll(r)
+		w.w.Event(clipboard.Event{Text: string(data)})
+	}()
 }
 
 func (w *window) WriteClipboard(s string) {
-	w.mu.Lock()
-	w.writeClipboard = &s
-	w.mu.Unlock()
-	w.disp.wakeup()
+	w.disp.writeClipboard([]byte(s))
 }
 
 func (w *window) Option(opts *Options) {
-	w.mu.Lock()
-	w.opts = opts
-	w.mu.Unlock()
-	w.disp.wakeup()
+	w.setOptions(opts)
 }
 
 func (w *window) setOptions(opts *Options) {
@@ -1138,48 +1131,21 @@ func (w *window) loop() error {
 		if err := w.disp.dispatch(&p); err != nil {
 			return err
 		}
+		select {
+		case <-w.wakeups:
+			w.w.Event(WakeupEvent{})
+		default:
+		}
 		if w.dead {
 			w.w.Event(system.DestroyEvent{})
 			break
 		}
-		w.process()
+		// pass false to skip unnecessary drawing.
+		w.draw(false)
 	}
 	return nil
 }
 
-func (w *window) process() {
-	w.mu.Lock()
-	readClipboard := w.readClipboard
-	writeClipboard := w.writeClipboard
-	opts := w.opts
-	w.readClipboard = false
-	w.writeClipboard = nil
-	w.opts = nil
-	w.mu.Unlock()
-	if readClipboard {
-		r, err := w.disp.readClipboard()
-		// Send empty responses on unavailable clipboards or errors.
-		if r == nil || err != nil {
-			w.w.Event(clipboard.Event{})
-			return
-		}
-		// Don't let slow clipboard transfers block event loop.
-		go func() {
-			defer r.Close()
-			data, _ := ioutil.ReadAll(r)
-			w.w.Event(clipboard.Event{Text: string(data)})
-		}()
-	}
-	if writeClipboard != nil {
-		w.disp.writeClipboard([]byte(*writeClipboard))
-	}
-	if opts != nil {
-		w.setOptions(opts)
-	}
-	// pass false to skip unnecessary drawing.
-	w.draw(false)
-}
-
 func (d *wlDisplay) dispatch(p *poller) error {
 	dispfd := C.wl_display_get_fd(d.disp)
 	// Poll for events and notifications.
@@ -1222,13 +1188,18 @@ func (d *wlDisplay) dispatch(p *poller) error {
 	return nil
 }
 
-func (w *window) SetAnimating(anim bool) {
-	w.mu.Lock()
-	w.animating = anim
-	w.mu.Unlock()
+func (w *window) Wakeup() {
+	select {
+	case w.wakeups <- struct{}{}:
+	default:
+	}
 	w.disp.wakeup()
 }
 
+func (w *window) SetAnimating(anim bool) {
+	w.animating = anim
+}
+
 // Wakeup wakes up the event loop through the notification pipe.
 func (d *wlDisplay) wakeup() {
 	oneByte := make([]byte, 1)
@@ -1415,12 +1386,10 @@ func (w *window) updateOutputs() {
 			}
 		}
 	}
-	w.mu.Lock()
 	if found && scale != w.scale {
 		w.scale = scale
 		w.newScale = true
 	}
-	w.mu.Unlock()
 	if !found {
 		w.setStage(system.StagePaused)
 	} else {
@@ -1439,10 +1408,8 @@ func (w *window) config() (int, int, unit.Metric) {
 
 func (w *window) draw(sync bool) {
 	w.flushScroll()
-	w.mu.Lock()
 	anim := w.animating || w.fling.anim.Active()
 	dead := w.dead
-	w.mu.Unlock()
 	if dead || (!anim && !sync) {
 		return
 	}

app/internal/wm/os_windows.go

@@ -59,7 +59,6 @@ type window struct {
 	// placement saves the previous window position when in full screen mode.
 	placement *windows.WindowPlacement
 
-	mu        sync.Mutex
 	animating bool
 
 	minmax winConstraints
@@ -67,11 +66,7 @@ type window struct {
 	opts   *Options
 }
 
-const (
-	_WM_REDRAW = windows.WM_USER + iota
-	_WM_CURSOR
-	_WM_OPTION
-)
+const _WM_WAKEUP = windows.WM_USER + iota
 
 type gpuAPI struct {
 	priority    int
@@ -330,14 +325,12 @@ func windowProc(hwnd syscall.Handle, msg uint32, wParam, lParam uintptr) uintptr
 		}
 	case windows.WM_SETCURSOR:
 		w.cursorIn = (lParam & 0xffff) == windows.HTCLIENT
-		fallthrough
-	case _WM_CURSOR:
 		if w.cursorIn {
 			windows.SetCursor(w.cursor)
 			return windows.TRUE
 		}
-	case _WM_OPTION:
-		w.setOptions()
+	case _WM_WAKEUP:
+		w.w.Event(WakeupEvent{})
 	}
 
 	return windows.DefWindowProc(hwnd, msg, wParam, lParam)
@@ -422,9 +415,7 @@ func (w *window) loop() error {
 	msg := new(windows.Msg)
 loop:
 	for {
-		w.mu.Lock()
 		anim := w.animating
-		w.mu.Unlock()
 		if anim && !windows.PeekMessage(msg, 0, 0, 0, windows.PM_NOREMOVE) {
 			w.draw(false)
 			continue
@@ -443,16 +434,11 @@ loop:
 }
 
 func (w *window) SetAnimating(anim bool) {
-	w.mu.Lock()
 	w.animating = anim
-	w.mu.Unlock()
-	if anim {
-		w.postRedraw()
-	}
 }
 
-func (w *window) postRedraw() {
-	if err := windows.PostMessage(w.hwnd, _WM_REDRAW, 0, 0); err != nil {
+func (w *window) Wakeup() {
+	if err := windows.PostMessage(w.hwnd, _WM_WAKEUP, 0, 0); err != nil {
 		panic(err)
 	}
 }
@@ -530,18 +516,7 @@ func (w *window) readClipboard() error {
 }
 
 func (w *window) Option(opts *Options) {
-	w.mu.Lock()
 	w.opts = opts
-	w.mu.Unlock()
-	if err := windows.PostMessage(w.hwnd, _WM_OPTION, 0, 0); err != nil {
-		panic(err)
-	}
-}
-
-func (w *window) setOptions() {
-	w.mu.Lock()
-	opts := w.opts
-	w.mu.Unlock()
 	if o := opts.Size; o != nil {
 		dpi := windows.GetSystemDPI()
 		cfg := configForDPI(dpi)
@@ -658,8 +633,8 @@ func (w *window) SetCursor(name pointer.CursorName) {
 		c = resources.cursor
 	}
 	w.cursor = c
-	if err := windows.PostMessage(w.hwnd, _WM_CURSOR, 0, 0); err != nil {
-		panic(err)
+	if w.cursorIn {
+		windows.SetCursor(w.cursor)
 	}
 }
 

app/internal/wm/os_x11.go

@@ -87,59 +87,34 @@ type x11Window struct {
 	}
 	dead bool
 
-	mu        sync.Mutex
 	animating bool
-	opts      *Options
 
 	pointerBtns pointer.Buttons
 
 	clipboard struct {
-		read    bool
-		write   *string
 		content []byte
 	}
 	cursor pointer.CursorName
 	mode   WindowMode
+
+	wakeups chan struct{}
 }
 
 func (w *x11Window) SetAnimating(anim bool) {
-	w.mu.Lock()
 	w.animating = anim
-	w.mu.Unlock()
-	if anim {
-		w.wakeup()
-	}
 }
 
 func (w *x11Window) ReadClipboard() {
-	w.mu.Lock()
-	w.clipboard.read = true
-	w.mu.Unlock()
-	w.wakeup()
+	C.XDeleteProperty(w.x, w.xw, w.atoms.clipboardContent)
+	C.XConvertSelection(w.x, w.atoms.clipboard, w.atoms.utf8string, w.atoms.clipboardContent, w.xw, C.CurrentTime)
 }
 
 func (w *x11Window) WriteClipboard(s string) {
-	w.mu.Lock()
-	w.clipboard.write = &s
-	w.mu.Unlock()
-	w.wakeup()
+	w.clipboard.content = []byte(s)
+	C.XSetSelectionOwner(w.x, w.atoms.clipboard, w.xw, C.CurrentTime)
 }
 
 func (w *x11Window) Option(opts *Options) {
-	w.mu.Lock()
-	w.opts = opts
-	w.mu.Unlock()
-	w.wakeup()
-}
-
-func (w *x11Window) setOptions() {
-	w.mu.Lock()
-	opts := w.opts
-	w.opts = nil
-	w.mu.Unlock()
-	if opts == nil {
-		return
-	}
 	var shints C.XSizeHints
 	if o := opts.MinSize; o != nil {
 		shints.min_width = C.int(w.cfg.Px(o.Width))
@@ -250,9 +225,6 @@ func (w *x11Window) ShowTextInput(show bool) {}
 
 // Close the window.
 func (w *x11Window) Close() {
-	w.mu.Lock()
-	defer w.mu.Unlock()
-
 	var xev C.XEvent
 	ev := (*C.XClientMessageEvent)(unsafe.Pointer(&xev))
 	*ev = C.XClientMessageEvent{
@@ -270,7 +242,11 @@ func (w *x11Window) Close() {
 
 var x11OneByte = make([]byte, 1)
 
-func (w *x11Window) wakeup() {
+func (w *x11Window) Wakeup() {
+	select {
+	case w.wakeups <- struct{}{}:
+	default:
+	}
 	if _, err := syscall.Write(w.notify.write, x11OneByte); err != nil && err != syscall.EAGAIN {
 		panic(fmt.Errorf("failed to write to pipe: %v", err))
 	}
@@ -312,9 +288,7 @@ loop:
 		// This fixes an issue on Xephyr where on startup XPending() > 0 but
 		// poll will still block. This also prevents no-op calls to poll.
 		if syn = h.handleEvents(); !syn {
-			w.mu.Lock()
 			anim = w.animating
-			w.mu.Unlock()
 			if !anim {
 				// Clear poll events.
 				*xEvents = 0
@@ -333,7 +307,6 @@ loop:
 				}
 			}
 		}
-		w.setOptions()
 		// Clear notifications.
 		for {
 			_, err := syscall.Read(w.notify.read, buf)
@@ -344,6 +317,11 @@ loop:
 				panic(fmt.Errorf("x11 loop: read from notify pipe failed: %w", err))
 			}
 		}
+		select {
+		case <-w.wakeups:
+			w.w.Event(WakeupEvent{})
+		default:
+		}
 
 		if anim || syn {
 			w.w.Event(FrameEvent{
@@ -358,20 +336,6 @@ loop:
 				Sync: syn,
 			})
 		}
-		w.mu.Lock()
-		readClipboard := w.clipboard.read
-		writeClipboard := w.clipboard.write
-		w.clipboard.read = false
-		w.clipboard.write = nil
-		w.mu.Unlock()
-		if readClipboard {
-			C.XDeleteProperty(w.x, w.xw, w.atoms.clipboardContent)
-			C.XConvertSelection(w.x, w.atoms.clipboard, w.atoms.utf8string, w.atoms.clipboardContent, w.xw, C.CurrentTime)
-		}
-		if writeClipboard != nil {
-			w.clipboard.content = []byte(*writeClipboard)
-			C.XSetSelectionOwner(w.x, w.atoms.clipboard, w.xw, C.CurrentTime)
-		}
 	}
 	w.w.Event(system.DestroyEvent{Err: nil})
 }
@@ -681,6 +645,7 @@ func newX11Window(gioWin Callbacks, opts *Options) error {
 		cfg:          cfg,
 		xkb:          xkb,
 		xkbEventBase: xkbEventBase,
+		wakeups:      make(chan struct{}, 1),
 	}
 	w.notify.read = pipe[0]
 	w.notify.write = pipe[1]

app/internal/wm/window.go

@@ -32,6 +32,8 @@ type Options struct {
 	CustomRenderer  bool
 }
 
+type WakeupEvent struct{}
+
 type WindowMode uint8
 
 const (
@@ -59,7 +61,7 @@ type Callbacks interface {
 	// Func runs a function during an Event. This is required for platforms
 	// that require coordination between the rendering goroutine and the system
 	// main thread.
-	Func(f func())
+	Run(f func())
 }
 
 type Context interface {
@@ -99,6 +101,8 @@ type Driver interface {
 
 	// Close the window.
 	Close()
+	// Wakeup wakes up the event loop and sends a WakeupEvent.
+	Wakeup()
 }
 
 type windowRendezvous struct {
@@ -137,3 +141,5 @@ func newWindowRendezvous() *windowRendezvous {
 	}()
 	return wr
 }
+
+func (_ WakeupEvent) ImplementsEvent() {}

app/window.go

@@ -24,7 +24,7 @@ import (
 // WindowOption configures a wm.
 type Option func(opts *wm.Options)
 
-// Window represents an operating system wm.
+// Window represents an operating system window.
 type Window struct {
 	driver wm.Driver
 	ctx    wm.Context
@@ -33,6 +33,9 @@ type Window struct {
 	// driverFuncs is a channel of functions to run when
 	// the Window has a valid driver.
 	driverFuncs chan func()
+	// wakeups wakes up the native event loop to send a
+	// wm.WakeupEvent that flushes driverFuncs.
+	wakeups chan struct{}
 
 	out         chan event.Event
 	in          chan event.Event
@@ -41,7 +44,8 @@ type Window struct {
 	frames      chan *op.Ops
 	frameAck    chan struct{}
 	// dead is closed when the window is destroyed.
-	dead chan struct{}
+	dead          chan struct{}
+	notifyAnimate chan struct{}
 
 	stage        system.Stage
 	animating    bool
@@ -58,8 +62,7 @@ type Window struct {
 }
 
 type callbacks struct {
-	w     *Window
-	funcs chan func()
+	w *Window
 }
 
 // queue is an event.Queue implementation that distributes system events
@@ -98,17 +101,18 @@ func NewWindow(options ...Option) *Window {
 	}
 
 	w := &Window{
-		in:          make(chan event.Event),
-		out:         make(chan event.Event),
-		ack:         make(chan struct{}),
-		invalidates: make(chan struct{}, 1),
-		frames:      make(chan *op.Ops),
-		frameAck:    make(chan struct{}),
-		driverFuncs: make(chan func()),
-		dead:        make(chan struct{}),
-		nocontext:   opts.CustomRenderer,
+		in:            make(chan event.Event),
+		out:           make(chan event.Event),
+		ack:           make(chan struct{}),
+		invalidates:   make(chan struct{}, 1),
+		frames:        make(chan *op.Ops),
+		frameAck:      make(chan struct{}),
+		driverFuncs:   make(chan func(), 1),
+		wakeups:       make(chan struct{}, 1),
+		dead:          make(chan struct{}),
+		notifyAnimate: make(chan struct{}, 1),
+		nocontext:     opts.CustomRenderer,
 	}
-	w.callbacks.funcs = make(chan func())
 	w.callbacks.w = w
 	go w.run(opts)
 	return w
@@ -177,9 +181,9 @@ func (w *Window) processFrame(frameStart time.Time, size image.Point, frame *op.
 	w.queue.q.Frame(frame)
 	switch w.queue.q.TextInputState() {
 	case router.TextInputOpen:
-		w.driver.ShowTextInput(true)
+		go w.Run(func() { w.driver.ShowTextInput(true) })
 	case router.TextInputClose:
-		w.driver.ShowTextInput(false)
+		go w.Run(func() { w.driver.ShowTextInput(false) })
 	}
 	if txt, ok := w.queue.q.WriteClipboard(); ok {
 		go w.WriteClipboard(txt)
@@ -226,7 +230,7 @@ func (w *Window) Invalidate() {
 
 // Option applies the options to the window.
 func (w *Window) Option(opts ...Option) {
-	go w.driverDo(func() {
+	go w.Run(func() {
 		o := new(wm.Options)
 		for _, opt := range opts {
 			opt(o)
@@ -239,21 +243,21 @@ func (w *Window) Option(opts ...Option) {
 // of a clipboard.Event. Multiple reads may be coalesced
 // to a single event.
 func (w *Window) ReadClipboard() {
-	go w.driverDo(func() {
+	go w.Run(func() {
 		w.driver.ReadClipboard()
 	})
 }
 
 // WriteClipboard writes a string to the clipboard.
 func (w *Window) WriteClipboard(s string) {
-	go w.driverDo(func() {
+	go w.Run(func() {
 		w.driver.WriteClipboard(s)
 	})
 }
 
 // SetCursorName changes the current window cursor to name.
 func (w *Window) SetCursorName(name pointer.CursorName) {
-	go w.driverDo(func() {
+	go w.Run(func() {
 		w.driver.SetCursor(name)
 	})
 }
@@ -264,16 +268,32 @@ func (w *Window) SetCursorName(name pointer.CursorName) {
 // Currently, only macOS, Windows and X11 drivers implement this functionality,
 // all others are stubbed.
 func (w *Window) Close() {
-	go w.driverDo(func() {
+	go w.Run(func() {
 		w.driver.Close()
 	})
 }
 
-// driverDo waits for the window to have a valid driver attached and calls f.
-// It does nothing if the if the window was destroyed while waiting.
-func (w *Window) driverDo(f func()) {
+// Run f in the same thread as the native window event loop, and wait for f to
+// return or the window to close. Run is guaranteed not to deadlock if it is
+// invoked during the handling of a ViewEvent, system.FrameEvent,
+// system.StageEvent; call Run in a separate goroutine to avoid deadlock in all
+// other cases.
+//
+// Note that most programs should not call Run; configuring a Window with
+// CustomRenderer is a notable exception.
+func (w *Window) Run(f func()) {
+	done := make(chan struct{})
+	wrapper := func() {
+		f()
+		close(done)
+	}
 	select {
-	case w.driverFuncs <- f:
+	case w.driverFuncs <- wrapper:
+		w.wakeup()
+		select {
+		case <-done:
+		case <-w.dead:
+		}
 	case <-w.dead:
 	}
 }
@@ -293,7 +313,18 @@ func (w *Window) updateAnimation() {
 	}
 	if animate != w.animating {
 		w.animating = animate
-		w.driver.SetAnimating(animate)
+		select {
+		case w.notifyAnimate <- struct{}{}:
+			w.wakeup()
+		default:
+		}
+	}
+}
+
+func (w *Window) wakeup() {
+	select {
+	case w.wakeups <- struct{}{}:
+	default:
 	}
 }
 
@@ -311,20 +342,39 @@ func (c *callbacks) SetDriver(d wm.Driver) {
 func (c *callbacks) Event(e event.Event) {
 	select {
 	case c.w.in <- e:
-		for {
-			select {
-			case <-c.w.ack:
-				return
-			case f := <-c.funcs:
-				f()
-			}
-		}
+		c.w.runFuncs()
 	case <-c.w.dead:
 	}
 }
 
-func (c *callbacks) Func(f func()) {
-	c.funcs <- f
+func (w *Window) runFuncs() {
+	// Flush pending runnnables.
+loop:
+	for {
+		select {
+		case <-w.notifyAnimate:
+			w.driver.SetAnimating(w.animating)
+		case f := <-w.driverFuncs:
+			f()
+		default:
+			break loop
+		}
+	}
+	// Wait for ack while running incoming runnables.
+	for {
+		select {
+		case <-w.notifyAnimate:
+			w.driver.SetAnimating(w.animating)
+		case f := <-w.driverFuncs:
+			f()
+		case <-w.ack:
+			return
+		}
+	}
+}
+
+func (c *callbacks) Run(f func()) {
+	c.w.Run(f)
 }
 
 func (w *Window) waitAck() {
@@ -383,9 +433,9 @@ func (w *Window) run(opts *wm.Options) {
 		return
 	}
 	for {
-		var driverFuncs chan func()
+		var wakeups chan struct{}
 		if w.driver != nil {
-			driverFuncs = w.driverFuncs
+			wakeups = w.wakeups
 		}
 		var timer <-chan time.Time
 		if w.delayedDraw != nil {
@@ -398,8 +448,8 @@ func (w *Window) run(opts *wm.Options) {
 		case <-w.invalidates:
 			w.setNextFrame(time.Time{})
 			w.updateAnimation()
-		case f := <-driverFuncs:
-			f()
+		case <-wakeups:
+			w.driver.Wakeup()
 		case e := <-w.in:
 			switch e2 := e.(type) {
 			case system.StageEvent:
@@ -454,6 +504,10 @@ func (w *Window) run(opts *wm.Options) {
 				w.out <- e2
 				w.ack <- struct{}{}
 				return
+			case ViewEvent:
+				w.out <- e2
+				w.waitAck()
+			case wm.WakeupEvent:
 			case event.Event:
 				if w.queue.q.Queue(e2) {
 					w.setNextFrame(time.Time{})