Fix two race conditions and a type conversion mistake

flutter/flutter.go

@@ -8,15 +8,20 @@ package flutter
 import "C"
 import (
 	"encoding/json"
+	"sync"
 	"unsafe"
 )
 
 // the current FlutterEngine running (associated with his callback)
 var flutterEngines []*EngineOpenGL
+var flutterEnginesLock sync.RWMutex
 
 // SelectEngine return a EngineOpenGL from an index
 func SelectEngine(index int) *EngineOpenGL {
-	return flutterEngines[index]
+	flutterEnginesLock.RLock()
+	engine := flutterEngines[index]
+	flutterEnginesLock.RUnlock()
+	return engine
 }
 
 // NumberOfEngines return the number of engine registered into this embedder
@@ -40,6 +45,9 @@ type EngineOpenGL struct {
 	// Flutter Engine.
 	Engine C.FlutterEngine
 
+	// index of the engine in the global flutterEngines slice
+	index int
+
 	// Necessary callbacks for rendering.
 	FMakeCurrent         func(v unsafe.Pointer) bool
 	FClearCurrent        func(v unsafe.Pointer) bool
@@ -56,11 +64,24 @@ type EngineOpenGL struct {
 	IcuDataPath string
 }
 
-// Run launches the Flutter Engine in a background thread.
-func (flu *EngineOpenGL) Run(window uintptr, vmArgs []string) Result {
-
+// NewEngineOpenGL creates an empty EngineOpenGL
+// and assigns it an index for global lookup.
+func NewEngineOpenGL() *EngineOpenGL {
+	flu := &EngineOpenGL{}
+	flutterEnginesLock.Lock()
 	flutterEngines = append(flutterEngines, flu)
+	flu.index = len(flutterEngines) - 1
+	flutterEnginesLock.Unlock()
+	return flu
+}
 
+// Index returns the index of the engine in the global flutterEngines slice
+func (flu *EngineOpenGL) Index() int {
+	return flu.index
+}
+
+// Run launches the Flutter Engine in a background thread.
+func (flu *EngineOpenGL) Run(window uintptr, vmArgs []string) Result {
 	args := C.FlutterProjectArgs{
 		assets_path:   C.CString(flu.AssetsPath),
 		main_path:     C.CString(""),

flutter/flutter_proxy_glfw.go

@@ -18,7 +18,7 @@ import (
 // C proxies
 
 //export proxy_on_platform_message
-func proxy_on_platform_message(message *C.FlutterPlatformMessage, userPointer unsafe.Pointer) C.bool {
+func proxy_on_platform_message(message *C.FlutterPlatformMessage, window unsafe.Pointer) C.bool {
 	if message.message != nil {
 		str := C.GoStringN(C.c_str(message.message), C.int(message.message_size))
 
@@ -30,43 +30,49 @@ func proxy_on_platform_message(message *C.FlutterPlatformMessage, userPointer un
 			Channel:        C.GoString(message.channel),
 			ResponseHandle: message.response_handle,
 		}
-		return C.bool(flutterEngines[0].FPlatfromMessage(FlutterPlatformMessage, userPointer))
+		index := *(*int)(glfw.GoWindow(window).GetUserPointer())
+		engine := SelectEngine(index)
+		return C.bool(engine.FPlatfromMessage(FlutterPlatformMessage, window))
 	}
 	return C.bool(false)
-
 }
 
 //export proxy_make_current
 func proxy_make_current(v unsafe.Pointer) C.bool {
 	w := glfw.GoWindow(v)
-	index := *(*C.int)(w.GetUserPointer())
-	return C.bool(flutterEngines[index].FMakeCurrent(v))
+	index := *(*int)(w.GetUserPointer())
+	engine := SelectEngine(index)
+	return C.bool(engine.FMakeCurrent(v))
 }
 
 //export proxy_clear_current
 func proxy_clear_current(v unsafe.Pointer) C.bool {
 	w := glfw.GoWindow(v)
-	index := *(*C.int)(w.GetUserPointer())
-	return C.bool(flutterEngines[index].FClearCurrent(v))
+	index := *(*int)(w.GetUserPointer())
+	engine := SelectEngine(index)
+	return C.bool(engine.FClearCurrent(v))
 }
 
 //export proxy_present
 func proxy_present(v unsafe.Pointer) C.bool {
 	w := glfw.GoWindow(v)
-	index := *(*C.int)(w.GetUserPointer())
-	return C.bool(flutterEngines[index].FPresent(v))
+	index := *(*int)(w.GetUserPointer())
+	engine := SelectEngine(index)
+	return C.bool(engine.FPresent(v))
 }
 
 //export proxy_fbo_callback
 func proxy_fbo_callback(v unsafe.Pointer) C.uint32_t {
 	w := glfw.GoWindow(v)
-	index := *(*C.int)(w.GetUserPointer())
-	return C.uint32_t(flutterEngines[index].FFboCallback(v))
+	index := *(*int)(w.GetUserPointer())
+	engine := SelectEngine(index)
+	return C.uint32_t(engine.FFboCallback(v))
 }
 
 //export proxy_make_resource_current
 func proxy_make_resource_current(v unsafe.Pointer) C.bool {
 	w := glfw.GoWindow(v)
-	index := *(*C.int)(w.GetUserPointer())
-	return C.bool(flutterEngines[index].FMakeResourceCurrent(v))
+	index := *(*int)(w.GetUserPointer())
+	engine := SelectEngine(index)
+	return C.bool(engine.FMakeResourceCurrent(v))
 }

gutter.go

@@ -184,33 +184,32 @@ func glfwCharCallback(w *glfw.Window, char rune) {
 // Flutter Engine
 func runFlutter(window *glfw.Window, c config) *flutter.EngineOpenGL {
 
-	flutterOGL := flutter.EngineOpenGL{
-		// Engine arguments
-		AssetsPath:  c.AssetPath,
-		IcuDataPath: c.ICUDataPath,
-		// Render callbacks
-		FMakeCurrent: func(v unsafe.Pointer) bool {
-			w := glfw.GoWindow(v)
-			w.MakeContextCurrent()
-			return true
-		},
-		FClearCurrent: func(v unsafe.Pointer) bool {
-			glfw.DetachCurrentContext()
-			return true
-		},
-		FPresent: func(v unsafe.Pointer) bool {
-			w := glfw.GoWindow(v)
-			w.SwapBuffers()
-			return true
-		},
-		FFboCallback: func(v unsafe.Pointer) int32 {
-			return 0
-		},
-		FMakeResourceCurrent: func(v unsafe.Pointer) bool {
-			return false
-		},
-		PixelRatio: c.PixelRatio,
+	flutterOGL := flutter.NewEngineOpenGL()
+	// Engine arguments
+	flutterOGL.AssetsPath = c.AssetPath
+	flutterOGL.IcuDataPath = c.ICUDataPath
+	// Render callbacks
+	flutterOGL.FMakeCurrent = func(v unsafe.Pointer) bool {
+		w := glfw.GoWindow(v)
+		w.MakeContextCurrent()
+		return true
 	}
+	flutterOGL.FClearCurrent = func(v unsafe.Pointer) bool {
+		glfw.DetachCurrentContext()
+		return true
+	}
+	flutterOGL.FPresent = func(v unsafe.Pointer) bool {
+		w := glfw.GoWindow(v)
+		w.SwapBuffers()
+		return true
+	}
+	flutterOGL.FFboCallback = func(v unsafe.Pointer) int32 {
+		return 0
+	}
+	flutterOGL.FMakeResourceCurrent = func(v unsafe.Pointer) bool {
+		return false
+	}
+	flutterOGL.PixelRatio = c.PixelRatio
 
 	// PlatformMessage
 	flutterOGL.FPlatfromMessage = func(platMessage *flutter.PlatformMessage, window unsafe.Pointer) bool {
@@ -221,7 +220,7 @@ func runFlutter(window *glfw.Window, c config) *flutter.EngineOpenGL {
 		// Dispatch the message from the Flutter Engine, to all of the PluginReceivers
 		// having the same flutter.PlatformMessage.Channel name
 		for _, receivers := range c.PlatformMessageReceivers[platMessage.Channel] {
-			hasDispatched = receivers(platMessage, &flutterOGL, windows) || hasDispatched
+			hasDispatched = receivers(platMessage, flutterOGL, windows) || hasDispatched
 		}
 
 		return hasDispatched
@@ -232,8 +231,8 @@ func runFlutter(window *glfw.Window, c config) *flutter.EngineOpenGL {
 		updateEditingState(window)
 	}
 
-	NbEngine := flutter.NumberOfEngines()
-	window.SetUserPointer(unsafe.Pointer(&NbEngine))
+	flutterOGLIndex := flutterOGL.Index()
+	window.SetUserPointer(unsafe.Pointer(&flutterOGLIndex))
 	result := flutterOGL.Run(window.GLFWWindow(), c.VMArguments)
 
 	if result != flutter.KSuccess {
@@ -255,7 +254,7 @@ func runFlutter(window *glfw.Window, c config) *flutter.EngineOpenGL {
 	window.SetFramebufferSizeCallback(glfwWindowSizeCallback)
 	window.SetMouseButtonCallback(glfwMouseButtonCallback)
 	window.SetCharCallback(glfwCharCallback)
-	return &flutterOGL
+	return flutterOGL
 }
 
 // Update the TextInput with the current state