Use the default microtask scheduler on all isolates except the UI isolate (#5068)

See https://github.com/flutter/flutter/issues/16846

lib/ui/dart_runtime_hooks.cc

@@ -62,8 +62,7 @@ static Dart_Handle GetClosure(Dart_Handle builtin_library, const char* name) {
   return closure;
 }
 
-static void InitDartInternal(Dart_Handle builtin_library,
-                             DartRuntimeHooks::IsolateType isolate_type) {
+static void InitDartInternal(Dart_Handle builtin_library, bool is_ui_isolate) {
   Dart_Handle print = GetClosure(builtin_library, "_getPrintClosure");
 
   Dart_Handle internal_library = Dart_LookupLibrary(ToDart("dart:_internal"));
@@ -71,7 +70,7 @@ static void InitDartInternal(Dart_Handle builtin_library,
   DART_CHECK_VALID(
       Dart_SetField(internal_library, ToDart("_printClosure"), print));
 
-  if (isolate_type == DartRuntimeHooks::MainIsolate) {
+  if (is_ui_isolate) {
     // Call |_setupHooks| to configure |VMLibraryHooks|.
     Dart_Handle method_name = Dart_NewStringFromCString("_setupHooks");
     DART_CHECK_VALID(Dart_Invoke(builtin_library, method_name, 0, NULL))
@@ -97,14 +96,12 @@ static void InitDartCore(Dart_Handle builtin, const std::string& script_uri) {
       Dart_SetField(core_library, ToDart("_uriBaseClosure"), get_base_url));
 }
 
-static void InitDartAsync(Dart_Handle builtin_library,
-                          DartRuntimeHooks::IsolateType isolate_type) {
+static void InitDartAsync(Dart_Handle builtin_library, bool is_ui_isolate) {
   Dart_Handle schedule_microtask;
-  if (isolate_type == DartRuntimeHooks::MainIsolate) {
+  if (is_ui_isolate) {
     schedule_microtask =
         GetClosure(builtin_library, "_getScheduleMicrotaskClosure");
   } else {
-    FXL_CHECK(isolate_type == DartRuntimeHooks::SecondaryIsolate);
     Dart_Handle isolate_lib = Dart_LookupLibrary(ToDart("dart:isolate"));
     Dart_Handle method_name =
         Dart_NewStringFromCString("_getIsolateScheduleImmediateClosure");
@@ -132,13 +129,13 @@ static void InitDartIO(Dart_Handle builtin_library,
       Dart_SetField(platform_type, ToDart("_localeClosure"), locale_closure));
 }
 
-void DartRuntimeHooks::Install(IsolateType isolate_type,
+void DartRuntimeHooks::Install(bool is_ui_isolate,
                                const std::string& script_uri) {
   Dart_Handle builtin = Dart_LookupLibrary(ToDart("dart:ui"));
   DART_CHECK_VALID(builtin);
-  InitDartInternal(builtin, isolate_type);
+  InitDartInternal(builtin, is_ui_isolate);
   InitDartCore(builtin, script_uri);
-  InitDartAsync(builtin, isolate_type);
+  InitDartAsync(builtin, is_ui_isolate);
   InitDartIO(builtin, script_uri);
 }
 

lib/ui/dart_runtime_hooks.h

@@ -13,12 +13,7 @@ namespace blink {
 
 class DartRuntimeHooks {
  public:
-  enum IsolateType {
-    MainIsolate,
-    SecondaryIsolate,
-  };
-
-  static void Install(IsolateType isolate_type, const std::string& script_uri);
+  static void Install(bool is_ui_isolate, const std::string& script_uri);
   static void RegisterNatives(tonic::DartLibraryNatives* natives);
 
  private:

runtime/dart_isolate.cc

@@ -220,7 +220,7 @@ bool DartIsolate::UpdateThreadPoolNames() const {
   return true;
 }
 
-bool DartIsolate::LoadLibraries() {
+bool DartIsolate::LoadLibraries(bool is_root_isolate) {
   TRACE_EVENT0("flutter", "DartIsolate::LoadLibraries");
   if (phase_ != Phase::Initialized) {
     return false;
@@ -234,9 +234,7 @@ bool DartIsolate::LoadLibraries() {
 
   const bool is_service_isolate = Dart_IsServiceIsolate(isolate());
 
-  DartRuntimeHooks::Install(is_service_isolate
-                                ? DartRuntimeHooks::SecondaryIsolate
-                                : DartRuntimeHooks::MainIsolate,
+  DartRuntimeHooks::Install(is_root_isolate && !is_service_isolate,
                             GetAdvisoryScriptURI());
 
   if (!is_service_isolate) {
@@ -675,7 +673,7 @@ DartIsolate::CreateDartVMAndEmbedderObjectPair(
     return {nullptr, {}};
   }
 
-  if (!embedder_isolate->LoadLibraries()) {
+  if (!embedder_isolate->LoadLibraries(is_root_isolate)) {
     *error =
         strdup("Embedder could not load libraries in the new Dart isolate.");
     FXL_DLOG(ERROR) << *error;

runtime/dart_isolate.h

@@ -114,7 +114,7 @@ class DartIsolate : public UIDartState {
   bool Initialize(Dart_Isolate isolate, bool is_root_isolate);
 
   FXL_WARN_UNUSED_RESULT
-  bool LoadLibraries();
+  bool LoadLibraries(bool is_root_isolate);
 
   bool UpdateThreadPoolNames() const;