src: allow non-Node.js TracingControllers

We do not need a Node.js-provided `v8::TracingController`, generally.
Loosen that restriction in order to make it easier for embedders
to provide their own subclass of `v8::TracingController`,
or none at all.

Refs: electron/electron@9c36576

Author: addaleax

src/api/environment.cc

@@ -496,6 +496,14 @@ MultiIsolatePlatform* GetMultiIsolatePlatform(IsolateData* env) {
 MultiIsolatePlatform* CreatePlatform(
     int thread_pool_size,
     node::tracing::TracingController* tracing_controller) {
+  return CreatePlatform(
+      thread_pool_size,
+      static_cast<v8::TracingController*>(tracing_controller));
+}
+
+MultiIsolatePlatform* CreatePlatform(
+    int thread_pool_size,
+    v8::TracingController* tracing_controller) {
   return MultiIsolatePlatform::Create(thread_pool_size, tracing_controller)
       .release();
 }
@@ -506,7 +514,7 @@ void FreePlatform(MultiIsolatePlatform* platform) {
 
 std::unique_ptr<MultiIsolatePlatform> MultiIsolatePlatform::Create(
     int thread_pool_size,
-    node::tracing::TracingController* tracing_controller) {
+    v8::TracingController* tracing_controller) {
   return std::make_unique<NodePlatform>(thread_pool_size, tracing_controller);
 }
 

src/node.h

@@ -329,7 +329,7 @@ class NODE_EXTERN MultiIsolatePlatform : public v8::Platform {
 
   static std::unique_ptr<MultiIsolatePlatform> Create(
       int thread_pool_size,
-      node::tracing::TracingController* tracing_controller = nullptr);
+      v8::TracingController* tracing_controller = nullptr);
 };
 
 enum IsolateSettingsFlags {
@@ -487,9 +487,13 @@ NODE_EXTERN MultiIsolatePlatform* GetMultiIsolatePlatform(Environment* env);
 NODE_EXTERN MultiIsolatePlatform* GetMultiIsolatePlatform(IsolateData* env);
 
 // Legacy variants of MultiIsolatePlatform::Create().
+// TODO(addaleax): Deprecate in favour of the v8::TracingController variant.
 NODE_EXTERN MultiIsolatePlatform* CreatePlatform(
     int thread_pool_size,
     node::tracing::TracingController* tracing_controller);
+NODE_EXTERN MultiIsolatePlatform* CreatePlatform(
+    int thread_pool_size,
+    v8::TracingController* tracing_controller);
 NODE_EXTERN void FreePlatform(MultiIsolatePlatform* platform);
 
 NODE_EXTERN void EmitBeforeExit(Environment* env);

src/node_platform.cc

@@ -13,7 +13,6 @@ using v8::Isolate;
 using v8::Object;
 using v8::Platform;
 using v8::Task;
-using node::tracing::TracingController;
 
 namespace {
 
@@ -325,12 +324,16 @@ void PerIsolatePlatformData::DecreaseHandleCount() {
 }
 
 NodePlatform::NodePlatform(int thread_pool_size,
-                           TracingController* tracing_controller) {
-  if (tracing_controller) {
+                           v8::TracingController* tracing_controller) {
+  if (tracing_controller != nullptr) {
     tracing_controller_ = tracing_controller;
   } else {
-    tracing_controller_ = new TracingController();
+    tracing_controller_ = new v8::TracingController();
   }
+  // TODO(addaleax): It's a bit icky that we use global state here, but we can't
+  // really do anything about it unless V8 starts exposing a way to access the
+  // current v8::Platform instance.
+  tracing::TraceEventHelper::SetTracingController(tracing_controller_);
   worker_thread_task_runner_ =
       std::make_shared<WorkerThreadsTaskRunner>(thread_pool_size);
 }
@@ -519,7 +522,7 @@ double NodePlatform::CurrentClockTimeMillis() {
   return SystemClockTimeMillis();
 }
 
-TracingController* NodePlatform::GetTracingController() {
+v8::TracingController* NodePlatform::GetTracingController() {
   CHECK_NOT_NULL(tracing_controller_);
   return tracing_controller_;
 }

src/node_platform.h

@@ -138,7 +138,7 @@ class WorkerThreadsTaskRunner {
 class NodePlatform : public MultiIsolatePlatform {
  public:
   NodePlatform(int thread_pool_size,
-               node::tracing::TracingController* tracing_controller);
+               v8::TracingController* tracing_controller);
   ~NodePlatform() override = default;
 
   void DrainTasks(v8::Isolate* isolate) override;
@@ -160,7 +160,7 @@ class NodePlatform : public MultiIsolatePlatform {
   bool IdleTasksEnabled(v8::Isolate* isolate) override;
   double MonotonicallyIncreasingTime() override;
   double CurrentClockTimeMillis() override;
-  node::tracing::TracingController* GetTracingController() override;
+  v8::TracingController* GetTracingController() override;
   bool FlushForegroundTasks(v8::Isolate* isolate) override;
 
   void RegisterIsolate(v8::Isolate* isolate, uv_loop_t* loop) override;
@@ -185,7 +185,7 @@ class NodePlatform : public MultiIsolatePlatform {
     IsolatePlatformDelegate*, std::shared_ptr<PerIsolatePlatformData>>;
   std::unordered_map<v8::Isolate*, DelegatePair> per_isolate_;
 
-  node::tracing::TracingController* tracing_controller_;
+  v8::TracingController* tracing_controller_;
   std::shared_ptr<WorkerThreadsTaskRunner> worker_thread_task_runner_;
 };
 

src/tracing/agent.cc

@@ -242,8 +242,9 @@ void TracingController::AddMetadataEvent(
       TRACE_EVENT_FLAG_NONE,
       CurrentTimestampMicroseconds(),
       CurrentCpuTimestampMicroseconds());
-  node::tracing::TraceEventHelper::GetAgent()->AddMetadataEvent(
-      std::move(trace_event));
+  Agent* node_agent = node::tracing::TraceEventHelper::GetAgent();
+  if (node_agent != nullptr)
+    node_agent->AddMetadataEvent(std::move(trace_event));
 }
 
 }  // namespace tracing

src/tracing/trace_event.cc

@@ -4,17 +4,23 @@ namespace node {
 namespace tracing {
 
 Agent* g_agent = nullptr;
+v8::TracingController* g_controller = nullptr;
 
 void TraceEventHelper::SetAgent(Agent* agent) {
   g_agent = agent;
+  g_controller = agent->GetTracingController();
 }
 
 Agent* TraceEventHelper::GetAgent() {
   return g_agent;
 }
 
-TracingController* TraceEventHelper::GetTracingController() {
-  return g_agent->GetTracingController();
+v8::TracingController* TraceEventHelper::GetTracingController() {
+  return g_controller;
+}
+
+void TraceEventHelper::SetTracingController(v8::TracingController* controller) {
+  g_controller = controller;
 }
 
 }  // namespace tracing

src/tracing/trace_event.h

@@ -314,7 +314,9 @@ const uint64_t kNoId = 0;
 // Refs: https://github.com/nodejs/node/pull/28724
 class NODE_EXTERN TraceEventHelper {
  public:
-  static TracingController* GetTracingController();
+  static v8::TracingController* GetTracingController();
+  static void SetTracingController(v8::TracingController* controller);
+
   static Agent* GetAgent();
   static void SetAgent(Agent* agent);
 };
@@ -505,9 +507,10 @@ static V8_INLINE void AddMetadataEventImpl(
     arg_convertibles[1].reset(reinterpret_cast<v8::ConvertableToTraceFormat*>(
         static_cast<intptr_t>(arg_values[1])));
   }
-  node::tracing::TracingController* controller =
-      node::tracing::TraceEventHelper::GetTracingController();
-  return controller->AddMetadataEvent(
+  node::tracing::Agent* agent =
+      node::tracing::TraceEventHelper::GetAgent();
+  if (agent == nullptr) return;
+  return agent->GetTracingController()->AddMetadataEvent(
       category_group_enabled, name, num_args, arg_names, arg_types, arg_values,
       arg_convertibles, flags);
 }