Disable the timeline in release mode on Android unless systrace is en…

…abled (flutter#32909)

common/settings.h

@@ -136,6 +136,7 @@ struct Settings {
   std::optional<std::vector<std::string>> trace_skia_allowlist;
   bool trace_startup = false;
   bool trace_systrace = false;
+  bool enable_timeline_event_handler = true;
   bool dump_skp_on_shader_compilation = false;
   bool cache_sksl = false;
   bool purge_persistent_cache = false;

fml/trace_event.cc

@@ -51,6 +51,11 @@ void TraceSetTimelineEventHandler(TimelineEventHandler handler) {
   gTimelineEventHandler = handler;
 }
 
+bool TraceHasTimelineEventHandler() {
+  return static_cast<bool>(
+      gTimelineEventHandler.load(std::memory_order_relaxed));
+}
+
 void TraceSetTimelineMicrosSource(TimelineMicrosSource source) {
   gTimelineMicrosSource = source;
 }
@@ -307,6 +312,10 @@ void TraceSetAllowlist(const std::vector<std::string>& allowlist) {}
 
 void TraceSetTimelineEventHandler(TimelineEventHandler handler) {}
 
+bool TraceHasTimelineEventHandler() {
+  return false;
+}
+
 void TraceSetTimelineMicrosSource(TimelineMicrosSource source) {}
 
 size_t TraceNonce() {

fml/trace_event.h

@@ -159,6 +159,8 @@ using TimelineMicrosSource = int64_t (*)();
 
 void TraceSetTimelineEventHandler(TimelineEventHandler handler);
 
+bool TraceHasTimelineEventHandler();
+
 void TraceSetTimelineMicrosSource(TimelineMicrosSource source);
 
 void TraceTimelineEvent(TraceArg category_group,

runtime/dart_vm.cc

@@ -458,7 +458,8 @@ DartVM::DartVM(std::shared_ptr<const DartVMData> vm_data,
     params.thread_exit = ThreadExitCallback;
     params.get_service_assets = GetVMServiceAssetsArchiveCallback;
     params.entropy_source = dart::bin::GetEntropy;
-    DartVMInitializer::Initialize(&params);
+    DartVMInitializer::Initialize(&params,
+                                  settings_.enable_timeline_event_handler);
     // Send the earliest available timestamp in the application lifecycle to
     // timeline. The difference between this timestamp and the time we render
     // the very first frame gives us a good idea about Flutter's startup time.

runtime/dart_vm_initializer.cc

@@ -79,7 +79,8 @@ void ReportUnhandledException(Dart_Handle exception_handle,
 }
 }  // namespace
 
-void DartVMInitializer::Initialize(Dart_InitializeParams* params) {
+void DartVMInitializer::Initialize(Dart_InitializeParams* params,
+                                   bool enable_timeline_event_handler) {
   FML_DCHECK(!gDartInitialized);
 
   char* error = Dart_Initialize(params);
@@ -90,9 +91,12 @@ void DartVMInitializer::Initialize(Dart_InitializeParams* params) {
     gDartInitialized = true;
   }
 
+  if (enable_timeline_event_handler) {
+    fml::tracing::TraceSetTimelineMicrosSource(Dart_TimelineGetMicros);
+    fml::tracing::TraceSetTimelineEventHandler(LogDartTimelineEvent);
+  }
+
   fml::TimePoint::SetClockSource(flutter::DartTimelineTicksSinceEpoch);
-  fml::tracing::TraceSetTimelineEventHandler(LogDartTimelineEvent);
-  fml::tracing::TraceSetTimelineMicrosSource(Dart_TimelineGetMicros);
   tonic::SetUnhandledExceptionReporter(&ReportUnhandledException);
 }
 

runtime/dart_vm_initializer.h

@@ -10,7 +10,8 @@
 
 class DartVMInitializer {
  public:
-  static void Initialize(Dart_InitializeParams* params);
+  static void Initialize(Dart_InitializeParams* params,
+                         bool enable_timeline_event_handler);
   static void Cleanup();
 
  private:

runtime/dart_vm_unittests.cc

@@ -43,5 +43,14 @@ TEST_F(DartVMTest, OldGenHeapSize) {
   ASSERT_TRUE(vm);
 }
 
+TEST_F(DartVMTest, DisableTimelineEventHandler) {
+  ASSERT_FALSE(DartVMRef::IsInstanceRunning());
+  fml::tracing::TraceSetTimelineEventHandler(nullptr);
+  auto settings = CreateSettingsForFixture();
+  settings.enable_timeline_event_handler = false;
+  auto vm = DartVMRef::Create(settings);
+  ASSERT_FALSE(fml::tracing::TraceHasTimelineEventHandler());
+}
+
 }  // namespace testing
 }  // namespace flutter

shell/platform/android/flutter_main.cc

@@ -105,6 +105,12 @@ void FlutterMain::Init(JNIEnv* env,
     }
   }
 
+#if FLUTTER_RELEASE
+  // On most platforms the timeline is always disabled in release mode.
+  // On Android, enable it in release mode only when using systrace.
+  settings.enable_timeline_event_handler = settings.trace_systrace;
+#endif  // FLUTTER_RELEASE
+
   int64_t init_time_micros = initTimeMillis * 1000;
   settings.engine_start_timestamp =
       std::chrono::microseconds(Dart_TimelineGetMicros() - init_time_micros);