trace_events: background thread metadata events

src/node.cc

@@ -289,11 +289,11 @@ static struct {
 #if NODE_USE_V8_PLATFORM
   void Initialize(int thread_pool_size) {
     tracing_agent_.reset(new tracing::Agent(trace_file_pattern));
-    platform_ = new NodePlatform(thread_pool_size,
-        tracing_agent_->GetTracingController());
+    auto controller = tracing_agent_->GetTracingController();
+    tracing::TraceEventHelper::SetTracingController(controller);
+    StartTracingAgent();
+    platform_ = new NodePlatform(thread_pool_size, controller);
     V8::InitializePlatform(platform_);
-    tracing::TraceEventHelper::SetTracingController(
-        tracing_agent_->GetTracingController());
   }
 
   void Dispose() {
@@ -4406,8 +4406,6 @@ int Start(int argc, char** argv) {
 #endif  // HAVE_OPENSSL
 
   v8_platform.Initialize(v8_thread_pool_size);
-  // Enable tracing when argv has --trace-events-enabled.
-  v8_platform.StartTracingAgent();
   V8::Initialize();
   performance::performance_v8_start = PERFORMANCE_NOW();
   v8_initialized = true;

src/node_platform.cc

@@ -16,8 +16,10 @@ using v8::Platform;
 using v8::Task;
 using v8::TracingController;
 
-static void BackgroundRunner(void* data) {
-  TaskQueue<Task>* background_tasks = static_cast<TaskQueue<Task>*>(data);
+static void BackgroundRunner(void *data) {
+  TRACE_EVENT_METADATA1("__metadata", "thread_name", "name",
+                        "BackgroundTaskRunner");
+  TaskQueue<Task> *background_tasks = static_cast<TaskQueue<Task> *>(data);
   while (std::unique_ptr<Task> task = background_tasks->BlockingPop()) {
     task->Run();
     background_tasks->NotifyOfCompletion();

test/cctest/node_test_fixture.h

@@ -64,12 +64,12 @@ class NodeTestFixture : public ::testing::Test {
   v8::Isolate* isolate_;
 
   static void SetUpTestCase() {
-    platform.reset(new node::NodePlatform(4, nullptr));
     tracing_controller.reset(new v8::TracingController());
-    allocator.reset(v8::ArrayBuffer::Allocator::NewDefaultAllocator());
-    params.array_buffer_allocator = allocator.get();
     node::tracing::TraceEventHelper::SetTracingController(
         tracing_controller.get());
+    platform.reset(new node::NodePlatform(4, nullptr));
+    allocator.reset(v8::ArrayBuffer::Allocator::NewDefaultAllocator());
+    params.array_buffer_allocator = allocator.get();
     CHECK_EQ(0, uv_loop_init(&current_loop));
     v8::V8::InitializePlatform(platform.get());
     v8::V8::Initialize();

test/parallel/test-trace-events-metadata.js

@@ -22,5 +22,8 @@ proc.once('exit', common.mustCall(() => {
     assert(traces.some((trace) =>
       trace.cat === '__metadata' && trace.name === 'thread_name' &&
         trace.args.name === 'JavaScriptMainThread'));
+    assert(traces.some((trace) =>
+      trace.cat === '__metadata' && trace.name === 'thread_name' &&
+        trace.args.name === 'BackgroundTaskRunner'));
   }));
 }));