Avoid calling Dart_TimelineGetMicros when systrace is enabled (flutter#32968)

Author: dnfield

fml/trace_event.cc

@@ -56,6 +56,10 @@ bool TraceHasTimelineEventHandler() {
       gTimelineEventHandler.load(std::memory_order_relaxed));
 }
 
+int64_t TraceGetTimelineMicros() {
+  return gTimelineMicrosSource.load()();
+}
+
 void TraceSetTimelineMicrosSource(TimelineMicrosSource source) {
   gTimelineMicrosSource = source;
 }
@@ -316,6 +320,10 @@ bool TraceHasTimelineEventHandler() {
   return false;
 }
 
+int64_t TraceGetTimelineMicros() {
+  return -1;
+}
+
 void TraceSetTimelineMicrosSource(TimelineMicrosSource source) {}
 
 size_t TraceNonce() {

fml/trace_event.h

@@ -163,6 +163,8 @@ bool TraceHasTimelineEventHandler();
 
 void TraceSetTimelineMicrosSource(TimelineMicrosSource source);
 
+int64_t TraceGetTimelineMicros();
+
 void TraceTimelineEvent(TraceArg category_group,
                         TraceArg name,
                         int64_t timestamp_micros,

runtime/dart_vm.cc

@@ -463,7 +463,8 @@ DartVM::DartVM(std::shared_ptr<const DartVMData> vm_data,
     params.entropy_source = dart::bin::GetEntropy;
     params.get_service_assets = GetVMServiceAssetsArchiveCallback;
     DartVMInitializer::Initialize(&params,
-                                  settings_.enable_timeline_event_handler);
+                                  settings_.enable_timeline_event_handler,
+                                  settings_.trace_systrace);
     // 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

@@ -80,7 +80,8 @@ void ReportUnhandledException(Dart_Handle exception_handle,
 }  // namespace
 
 void DartVMInitializer::Initialize(Dart_InitializeParams* params,
-                                   bool enable_timeline_event_handler) {
+                                   bool enable_timeline_event_handler,
+                                   bool trace_systrace) {
   FML_DCHECK(!gDartInitialized);
 
   char* error = Dart_Initialize(params);
@@ -92,7 +93,16 @@ void DartVMInitializer::Initialize(Dart_InitializeParams* params,
   }
 
   if (enable_timeline_event_handler) {
-    fml::tracing::TraceSetTimelineMicrosSource(Dart_TimelineGetMicros);
+    if (!trace_systrace) {
+      // Systrace on all platforms except Fuchsia ignores the timestamp provided
+      // here. On Android in particular, calls to get the system clock show up
+      // in profiles.
+      // Fuchsia does not use the TraceSetTimelineMicrosSource.
+      fml::tracing::TraceSetTimelineMicrosSource(Dart_TimelineGetMicros);
+    } else {
+      fml::tracing::TraceSetTimelineMicrosSource(
+          []() -> int64_t { return -1; });
+    }
     fml::tracing::TraceSetTimelineEventHandler(LogDartTimelineEvent);
   }
 

runtime/dart_vm_initializer.h

@@ -11,7 +11,8 @@
 class DartVMInitializer {
  public:
   static void Initialize(Dart_InitializeParams* params,
-                         bool enable_timeline_event_handler);
+                         bool enable_timeline_event_handler,
+                         bool trace_systrace);
   static void Cleanup();
 
  private:

runtime/dart_vm_unittests.cc

@@ -52,5 +52,13 @@ TEST_F(DartVMTest, DisableTimelineEventHandler) {
   ASSERT_FALSE(fml::tracing::TraceHasTimelineEventHandler());
 }
 
+TEST_F(DartVMTest, TraceGetTimelineMicrosDoesNotGetClockWhenSystraceIsEnabled) {
+  ASSERT_FALSE(DartVMRef::IsInstanceRunning());
+  auto settings = CreateSettingsForFixture();
+  settings.trace_systrace = true;
+  auto vm = DartVMRef::Create(settings);
+  ASSERT_EQ(-1, fml::tracing::TraceGetTimelineMicros());
+}
+
 }  // namespace testing
 }  // namespace flutter