Use a signal for the pre-engine restart event (flutter/engine#55063)

With multiple FlViews a callback doesn't scale.

engine/src/flutter/shell/platform/linux/fl_engine.cc

@@ -62,11 +62,6 @@ struct _FlEngine {
   FlEngineUpdateSemanticsHandler update_semantics_handler;
   gpointer update_semantics_handler_data;
   GDestroyNotify update_semantics_handler_destroy_notify;
-
-  // Function to call right before the engine is restarted.
-  FlEngineOnPreEngineRestartHandler on_pre_engine_restart_handler;
-  gpointer on_pre_engine_restart_handler_data;
-  GDestroyNotify on_pre_engine_restart_handler_destroy_notify;
 };
 
 G_DEFINE_QUARK(fl_engine_error_quark, fl_engine_error)
@@ -74,6 +69,10 @@ G_DEFINE_QUARK(fl_engine_error_quark, fl_engine_error)
 static void fl_engine_plugin_registry_iface_init(
     FlPluginRegistryInterface* iface);
 
+enum { kSignalOnPreEngineRestart, kSignalLastSignal };
+
+static guint fl_engine_signals[kSignalLastSignal];
+
 G_DEFINE_TYPE_WITH_CODE(
     FlEngine,
     fl_engine,
@@ -343,10 +342,7 @@ static void fl_engine_update_semantics_cb(const FlutterSemanticsUpdate2* update,
 static void fl_engine_on_pre_engine_restart_cb(void* user_data) {
   FlEngine* self = FL_ENGINE(user_data);
 
-  if (self->on_pre_engine_restart_handler != nullptr) {
+  g_signal_emit(self, fl_engine_signals[kSignalOnPreEngineRestart], 0);
-    self->on_pre_engine_restart_handler(
-        self, self->on_pre_engine_restart_handler_data);
-  }
 }
 
 // Called when a response to a sent platform message is received from the
@@ -427,13 +423,6 @@ static void fl_engine_dispose(GObject* object) {
   self->update_semantics_handler_data = nullptr;
   self->update_semantics_handler_destroy_notify = nullptr;
 
-  if (self->on_pre_engine_restart_handler_destroy_notify) {
-    self->on_pre_engine_restart_handler_destroy_notify(
-        self->on_pre_engine_restart_handler_data);
-  }
-  self->on_pre_engine_restart_handler_data = nullptr;
-  self->on_pre_engine_restart_handler_destroy_notify = nullptr;
-
   G_OBJECT_CLASS(fl_engine_parent_class)->dispose(object);
 }
 
@@ -448,6 +437,10 @@ static void fl_engine_class_init(FlEngineClass* klass) {
           fl_binary_messenger_get_type(),
           static_cast<GParamFlags>(G_PARAM_WRITABLE | G_PARAM_CONSTRUCT_ONLY |
                                    G_PARAM_STATIC_STRINGS)));
+
+  fl_engine_signals[kSignalOnPreEngineRestart] = g_signal_new(
+      "on-pre-engine-restart", fl_engine_get_type(), G_SIGNAL_RUN_LAST, 0,
+      nullptr, nullptr, nullptr, G_TYPE_NONE, 0);
 }
 
 static void fl_engine_init(FlEngine* self) {
@@ -735,23 +728,6 @@ void fl_engine_set_update_semantics_handler(
   self->update_semantics_handler_destroy_notify = destroy_notify;
 }
 
-void fl_engine_set_on_pre_engine_restart_handler(
-    FlEngine* self,
-    FlEngineOnPreEngineRestartHandler handler,
-    gpointer user_data,
-    GDestroyNotify destroy_notify) {
-  g_return_if_fail(FL_IS_ENGINE(self));
-
-  if (self->on_pre_engine_restart_handler_destroy_notify) {
-    self->on_pre_engine_restart_handler_destroy_notify(
-        self->on_pre_engine_restart_handler_data);
-  }
-
-  self->on_pre_engine_restart_handler = handler;
-  self->on_pre_engine_restart_handler_data = user_data;
-  self->on_pre_engine_restart_handler_destroy_notify = destroy_notify;
-}
-
 // Note: This function can be called from any thread.
 gboolean fl_engine_send_platform_message_response(
     FlEngine* self,

engine/src/flutter/shell/platform/linux/fl_engine_private.h

@@ -60,16 +60,6 @@ typedef void (*FlEngineUpdateSemanticsHandler)(
     const FlutterSemanticsUpdate2* update,
     gpointer user_data);
 
-/**
- * FlEngineOnPreEngineRestartHandler:
- * @engine: an #FlEngine.
- * @user_data: (closure): data provided when registering this handler.
- *
- * Function called right before the engine is restarted.
- */
-typedef void (*FlEngineOnPreEngineRestartHandler)(FlEngine* engine,
-                                                  gpointer user_data);
-
 /**
  * fl_engine_new_with_renderer:
  * @project: an #FlDartProject.
@@ -218,22 +208,6 @@ void fl_engine_set_update_semantics_handler(
     gpointer user_data,
     GDestroyNotify destroy_notify);
 
-/**
- * fl_engine_set_on_pre_engine_restart_handler:
- * @engine: an #FlEngine.
- * @handler: function to call when the engine is restarted.
- * @user_data: (closure): user data to pass to @handler.
- * @destroy_notify: (allow-none): a function which gets called to free
- * @user_data, or %NULL.
- *
- * Registers the function called right before the engine is restarted.
- */
-void fl_engine_set_on_pre_engine_restart_handler(
-    FlEngine* engine,
-    FlEngineOnPreEngineRestartHandler handler,
-    gpointer user_data,
-    GDestroyNotify destroy_notify);
-
 /**
  * fl_engine_send_window_metrics_event:
  * @engine: an #FlEngine.

engine/src/flutter/shell/platform/linux/fl_engine_test.cc

@@ -275,14 +275,9 @@ void on_pre_engine_restart_cb(FlEngine* engine, gpointer user_data) {
   *count += 1;
 }
 
-void on_pre_engine_restart_destroy_notify(gpointer user_data) {
-  int* count = reinterpret_cast<int*>(user_data);
-  *count += 10;
-}
-
 // Checks restarting the engine invokes the correct callback.
 TEST(FlEngineTest, OnPreEngineRestart) {
-  FlEngine* engine = make_mock_engine();
+  g_autoptr(FlEngine) engine = make_mock_engine();
   FlutterEngineProcTable* embedder_api = fl_engine_get_embedder_api(engine);
 
   OnPreEngineRestartCallback callback;
@@ -317,16 +312,11 @@ TEST(FlEngineTest, OnPreEngineRestart) {
   //
   //  * When the engine restarts, count += 1;
   //  * When the engine is freed, count += 10.
-  fl_engine_set_on_pre_engine_restart_handler(
+  g_signal_connect(engine, "on-pre-engine-restart",
-      engine, on_pre_engine_restart_cb, &count,
+                   G_CALLBACK(on_pre_engine_restart_cb), &count);
-      on_pre_engine_restart_destroy_notify);
 
   callback(callback_user_data);
   EXPECT_EQ(count, 1);
-
-  // Disposal should call the destroy notify.
-  g_object_unref(engine);
-  EXPECT_EQ(count, 11);
 }
 
 TEST(FlEngineTest, DartEntrypointArgs) {

engine/src/flutter/shell/platform/linux/fl_view.cc

@@ -40,6 +40,9 @@ struct _FlView {
   // Engine this view is showing.
   FlEngine* engine;
 
+  // Handler for engine restart signal.
+  guint on_pre_engine_restart_handler;
+
   // ID for this view.
   FlutterViewId view_id;
 
@@ -274,9 +277,7 @@ static void update_semantics_cb(FlEngine* engine,
 // This method should reset states to be as if the engine had just been started,
 // which usually indicates the user has requested a hot restart (Shift-R in the
 // Flutter CLI.)
-static void on_pre_engine_restart_cb(FlEngine* engine, gpointer user_data) {
+static void on_pre_engine_restart_cb(FlView* self) {
-  FlView* self = FL_VIEW(user_data);
-
   init_keyboard(self);
   init_scrolling(self);
 }
@@ -652,8 +653,12 @@ static void fl_view_dispose(GObject* object) {
   if (self->engine != nullptr) {
     fl_engine_set_update_semantics_handler(self->engine, nullptr, nullptr,
                                            nullptr);
-    fl_engine_set_on_pre_engine_restart_handler(self->engine, nullptr, nullptr,
+  }
-                                                nullptr);
+
+  if (self->on_pre_engine_restart_handler != 0) {
+    g_signal_handler_disconnect(self->engine,
+                                self->on_pre_engine_restart_handler);
+    self->on_pre_engine_restart_handler = 0;
   }
 
   g_clear_object(&self->engine);
@@ -784,8 +789,9 @@ G_MODULE_EXPORT FlView* fl_view_new_for_engine(FlEngine* engine) {
 
   fl_engine_set_update_semantics_handler(self->engine, update_semantics_cb,
                                          self, nullptr);
-  fl_engine_set_on_pre_engine_restart_handler(
+  self->on_pre_engine_restart_handler =
-      self->engine, on_pre_engine_restart_cb, self, nullptr);
+      g_signal_connect_swapped(engine, "on-pre-engine-restart",
+                               G_CALLBACK(on_pre_engine_restart_cb), self);
 
   return self;
 }