flutter · knopp · Apr 30, 2025 · Mar 1, 2025 · Apr 17, 2025
diff --git a/engine/src/flutter/shell/platform/linux/fl_dart_project.cc b/engine/src/flutter/shell/platform/linux/fl_dart_project.cc
@@ -13,6 +13,8 @@ struct _FlDartProject {
   gchar* assets_path;
   gchar* icu_data_path;
   gchar** dart_entrypoint_args;
+
+  FlUIThreadPolicy ui_thread_policy;
 };
 
 G_DEFINE_TYPE(FlDartProject, fl_dart_project, G_TYPE_OBJECT)
@@ -114,3 +116,17 @@ G_MODULE_EXPORT void fl_dart_project_set_dart_entrypoint_arguments(
   g_clear_pointer(&self->dart_entrypoint_args, g_strfreev);
   self->dart_entrypoint_args = g_strdupv(argv);
 }
+
+G_MODULE_EXPORT
+void fl_dart_project_set_ui_thread_policy(FlDartProject* project,
+                                          FlUIThreadPolicy policy) {
+  g_return_if_fail(FL_IS_DART_PROJECT(project));
+  project->ui_thread_policy = policy;
+}
+
+G_MODULE_EXPORT
+FlUIThreadPolicy fl_dart_project_get_ui_thread_policy(FlDartProject* project) {
+  g_return_val_if_fail(FL_IS_DART_PROJECT(project),
+                       FL_UI_THREAD_POLICY_DEFAULT);
+  return project->ui_thread_policy;
+}
diff --git a/engine/src/flutter/shell/platform/linux/fl_engine.cc b/engine/src/flutter/shell/platform/linux/fl_engine.cc
@@ -637,6 +637,11 @@ gboolean fl_engine_start(FlEngine* self, GError** error) {
   custom_task_runners.struct_size = sizeof(FlutterCustomTaskRunners);
   custom_task_runners.platform_task_runner = &platform_task_runner;
 
+  if (fl_dart_project_get_ui_thread_policy(self->project) ==
+      FL_UI_THREAD_POLICY_RUN_ON_PLATFORM_THREAD) {
+    custom_task_runners.ui_task_runner = &platform_task_runner;
+  }
+
   g_autoptr(GPtrArray) command_line_args =
       g_ptr_array_new_with_free_func(g_free);
   g_ptr_array_insert(command_line_args, 0, g_strdup("flutter"));

diff --git a/engine/src/flutter/shell/platform/linux/fl_engine_test.cc b/engine/src/flutter/shell/platform/linux/fl_engine_test.cc
@@ -439,6 +439,57 @@ TEST(FlEngineTest, EngineId) {
   EXPECT_EQ(fl_engine_for_id(engine_id), engine);
 }
 
+TEST(FlEngineTest, UIIsolateOnPlatformTaskRunner) {
+  g_autoptr(FlDartProject) project = fl_dart_project_new();
+  g_autoptr(FlEngine) engine = fl_engine_new(project);
+  fl_dart_project_set_ui_thread_policy(
+      project, FL_UI_THREAD_POLICY_RUN_ON_PLATFORM_THREAD);
+
+  bool same_task_runner = false;
+
+  fl_engine_get_embedder_api(engine)->Initialize = MOCK_ENGINE_PROC(
+      Initialize,
+      ([&same_task_runner](size_t version, const FlutterRendererConfig* config,
+                           const FlutterProjectArgs* args, void* user_data,
+                           FLUTTER_API_SYMBOL(FlutterEngine) * engine_out) {
+        same_task_runner = args->custom_task_runners->platform_task_runner ==
+                           args->custom_task_runners->ui_task_runner;
+        return kSuccess;
+      }));
+  fl_engine_get_embedder_api(engine)->RunInitialized =
+      MOCK_ENGINE_PROC(RunInitialized, ([](auto engine) { return kSuccess; }));
+
+  g_autoptr(GError) error = nullptr;
+  EXPECT_TRUE(fl_engine_start(engine, &error));
+  EXPECT_EQ(error, nullptr);
+  EXPECT_TRUE(same_task_runner);
+}
+
+TEST(FlEngineTest, UIIsolateOnSeparateThread) {
+  g_autoptr(FlDartProject) project = fl_dart_project_new();
+  g_autoptr(FlEngine) engine = fl_engine_new(project);
+  fl_dart_project_set_ui_thread_policy(
+      project, FL_UI_THREAD_POLICY_RUN_ON_SEPARATE_THREAD);
+
+  bool separate_thread = false;
+
+  fl_engine_get_embedder_api(engine)->Initialize = MOCK_ENGINE_PROC(
+      Initialize,
+      ([&separate_thread](size_t version, const FlutterRendererConfig* config,
+                          const FlutterProjectArgs* args, void* user_data,
+                          FLUTTER_API_SYMBOL(FlutterEngine) * engine_out) {
+        separate_thread = args->custom_task_runners->ui_task_runner == nullptr;
+        return kSuccess;
+      }));
+  fl_engine_get_embedder_api(engine)->RunInitialized =
+      MOCK_ENGINE_PROC(RunInitialized, ([](auto engine) { return kSuccess; }));
+
+  g_autoptr(GError) error = nullptr;
+  EXPECT_TRUE(fl_engine_start(engine, &error));
+  EXPECT_EQ(error, nullptr);
+  EXPECT_TRUE(separate_thread);
+}
+
 TEST(FlEngineTest, Locales) {
   g_autofree gchar* initial_language = g_strdup(g_getenv("LANGUAGE"));
   g_setenv("LANGUAGE", "de:en_US", TRUE);

diff --git a/engine/src/flutter/shell/platform/linux/public/flutter_linux/fl_dart_project.h b/engine/src/flutter/shell/platform/linux/public/flutter_linux/fl_dart_project.h
@@ -128,6 +128,38 @@ void fl_dart_project_set_dart_entrypoint_arguments(FlDartProject* project,
  */
 gchar** fl_dart_project_get_dart_entrypoint_arguments(FlDartProject* project);
 
+/**
+ * FlUIThreadPolicy:
+ * Configures the thread policy for running the UI isolate.
+ * @FL_UI_THREAD_POLICY_DEFAULT: Defaut value. Currently will run the UI isolate
+ * on separate thread, later will change to run on platform thread.
+ * @FL_UI_THREAD_POLICY_RUN_ON_PLATFORM_THREAD: Run the UI isolate on the
+ * platform thread.
+ * @FL_UI_THREAD_POLICY_RUN_ON_SEPARATE_THREAD: Run the UI isolate on a separate
+ * thread.
+ */
+typedef enum {
+  FL_UI_THREAD_POLICY_DEFAULT,
+  FL_UI_THREAD_POLICY_RUN_ON_PLATFORM_THREAD,
+  FL_UI_THREAD_POLICY_RUN_ON_SEPARATE_THREAD,
+} FlUIThreadPolicy;
+
+/**
+ * fl_dart_project_set_ui_thread_policy:
+ * @project: an #FlDartProject.
+ * @policy: the thread policy to use for running the UI isolate.
+ */
+void fl_dart_project_set_ui_thread_policy(FlDartProject* project,
+                                          FlUIThreadPolicy policy);
+
+/**
+ * fl_dart_project_get_ui_thread_policy:
+ * @project: an #FlDartProject.
+ *
+ * Returns: the thread policy used for running the UI isolate.
+ */
+FlUIThreadPolicy fl_dart_project_get_ui_thread_policy(FlDartProject* project);
+
 G_END_DECLS
 
 #endif  // FLUTTER_SHELL_PLATFORM_LINUX_PUBLIC_FLUTTER_LINUX_FL_DART_PROJECT_H_