src: trace_events: background thread events

V8 uses a thread pool provided by the host to schedule background tasks
for concurrent GC and compiation. Emit trace events to identify the
background threads. Ensure that the tracing infrastructure is started
before the thread pool is initialized.

PR-URL: https://github.com/nodejs/node/pull/20823
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

4 files changed, 14 insertions, 11 deletions

diff --git a/src/node.cc b/src/node.cc
index 5313063578..27fccca6ee 100644
--- a/src/node.cc
+++ b/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;
diff --git a/src/node_platform.cc b/src/node_platform.cc
index b8f1344727..2885c72ed7 100644
--- a/src/node_platform.cc
+++ b/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();
diff --git a/test/cctest/node_test_fixture.h b/test/cctest/node_test_fixture.h
index e0740a4709..f43cb56cd3 100644
--- a/test/cctest/node_test_fixture.h
+++ b/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();
diff --git a/test/parallel/test-trace-events-metadata.js b/test/parallel/test-trace-events-metadata.js
index f8fcdcfe5b..eccec1ecf0 100644
--- a/test/parallel/test-trace-events-metadata.js
+++ b/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'));
   }));
 }));