Add PlatformDispatcher.registerHotRestartListener. (#3)

Author: knopp

engine/src/flutter/lib/ui/fixtures/ui_test.dart

@@ -283,6 +283,24 @@ void hooksTests() async {
     expectEquals(name, 'testName');
   });
 
+  await test('invokeHotRestartListeners preserves callback zone', () {
+    late Zone innerZone;
+    late Zone runZone;
+    late String name;
+
+    runZoned(() {
+      innerZone = Zone.current;
+      PlatformDispatcher.instance.registerHotRestartListener(() {
+        runZone = Zone.current;
+        name = 'testName';
+      });
+    });
+
+    _callHook('_invokeHotRestartListeners', 0);
+    expectIdentical(runZone, innerZone);
+    expectEquals(name, 'testName');
+  });
+
   await test('_futureize successfully returns a value async', () async {
     String? callbacker(void Function(Object? arg) cb) {
       Timer.run(() {

engine/src/flutter/lib/ui/hooks.dart

@@ -24,6 +24,11 @@ void _dispatchPlatformMessage(String name, ByteData? data, int responseId) {
   PlatformDispatcher.instance._dispatchPlatformMessage(name, data, responseId);
 }
 
+@pragma('vm:entry-point')
+void _invokeHotRestartListeners() {
+  PlatformDispatcher.instance._invokeHotRestartListeners();
+}
+
 @pragma('vm:entry-point')
 bool _onError(Object error, StackTrace? stackTrace) {
   return PlatformDispatcher.instance._dispatchError(error, stackTrace ?? StackTrace.empty);

engine/src/flutter/lib/ui/platform_dispatcher.dart

@@ -267,6 +267,29 @@ class PlatformDispatcher {
     }
   }
 
+  /// Registers a callback to be called when the application receives a hot restart signal.
+  void registerHotRestartListener(VoidCallback callback) {
+    _hotRestartListeners.add((callback, Zone.current));
+  }
+
+  /// Unregisters a callback from being called when the application receives a hot restart signal.
+  void unregisterHotRestartListener(VoidCallback callback) {
+    _hotRestartListeners.remove((callback, Zone.current));
+  }
+
+  void _invokeHotRestartListeners() {
+    final callbacks = List<(VoidCallback, Zone)>.from(_hotRestartListeners);
+    for (final (callback, zone) in callbacks) {
+      try {
+        _invoke(callback, zone);
+      } catch (e, s) {
+        onError?.call(e, s);
+      }
+    }
+  }
+
+  final List<(VoidCallback, Zone)> _hotRestartListeners = <(VoidCallback, Zone)>[];
+
   /// Set the debug name associated with this platform dispatcher's root
   /// isolate.
   ///

engine/src/flutter/lib/ui/window/platform_configuration.cc

@@ -43,6 +43,9 @@ void PlatformConfiguration::DidCreateIsolate() {
   dispatch_platform_message_.Set(
       tonic::DartState::Current(),
       Dart_GetField(library, tonic::ToDart("_dispatchPlatformMessage")));
+  invoke_hot_restart_listeners_.Set(
+      tonic::DartState::Current(),
+      Dart_GetField(library, tonic::ToDart("_invokeHotRestartListeners")));
 }
 
 bool PlatformConfiguration::SetEngineId(int64_t engine_id) {
@@ -59,6 +62,17 @@ bool PlatformConfiguration::SetEngineId(int64_t engine_id) {
   return true;
 }
 
+void PlatformConfiguration::InvokeHotRestartListeners() {
+  std::shared_ptr<tonic::DartState> dart_state =
+      invoke_hot_restart_listeners_.dart_state().lock();
+  if (!dart_state) {
+    return;
+  }
+  tonic::DartState::Scope scope(dart_state);
+  tonic::CheckAndHandleError(
+      tonic::DartInvoke(invoke_hot_restart_listeners_.Get(), {}));
+}
+
 void PlatformConfiguration::UpdateLocales(
     const std::vector<std::string>& locales) {
   std::shared_ptr<tonic::DartState> dart_state =

engine/src/flutter/lib/ui/window/platform_configuration.h

@@ -220,6 +220,9 @@ class PlatformConfiguration final {
   /// @return    Whether the identifier was set.
   bool SetEngineId(int64_t engine_id);
 
+  /// @brief     Calls registered hot restart listener callbacks.
+  void InvokeHotRestartListeners();
+
   //----------------------------------------------------------------------------
   /// @brief      Update the specified locale data in the framework.
   ///
@@ -268,6 +271,7 @@ class PlatformConfiguration final {
   tonic::DartPersistentValue set_engine_id_;
   tonic::DartPersistentValue update_locales_;
   tonic::DartPersistentValue dispatch_platform_message_;
+  tonic::DartPersistentValue invoke_hot_restart_listeners_;
 
   // ID starts at 1 because an ID of 0 indicates that no response is expected.
   int next_response_id_ = 1;

engine/src/flutter/shell/common/engine.cc

@@ -117,6 +117,10 @@ bool Engine::Restart(RunConfiguration configuration) {
     FML_LOG(ERROR) << "Engine run configuration was invalid.";
     return false;
   }
+  auto isolate = runtime_controller_->GetRootIsolate().lock();
+  if (isolate) {
+    isolate->platform_configuration()->InvokeHotRestartListeners();
+  }
   delegate_.OnPreEngineRestart();
   runtime_controller_ = runtime_controller_->Clone();
   UpdateAssetManager(nullptr);

examples/hello_world/lib/main.dart

@@ -1,3 +1,9 @@
+import 'dart:ui';
+
 void main() {
   print('Hello there...');
+
+  PlatformDispatcher.instance.registerHotRestartListener(() {
+    print('Hot restart listener called!');
+  });
 }