trace_events: fix trace events JS API writing

The Trace Events JS API isn't functional if none of
--trace-events-enabled or --trace-event-categories is passed as a CLI
argument. This commit fixes that.

In addition, we currently don't test the trace_events JS API in the
casewhere no CLI args are provided. This commit adds that test.

Fixes https://github.com/nodejs/node/issues/24944

PR-URL: https://github.com/nodejs/node/pull/24945
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ali Ijaz Sheikh <ofrobots@google.com>

1 files changed, 12 insertions, 4 deletions

diff --git a/src/node_v8_platform-inl.h b/src/node_v8_platform-inl.h
index ed91ee3a02..2c89ee9e52 100644
--- a/src/node_v8_platform-inl.h
+++ b/src/node_v8_platform-inl.h
@@ -85,7 +85,11 @@ struct V8Platform {
         tracing_agent_->GetTracingController();
     trace_state_observer_.reset(new NodeTraceStateObserver(controller));
     controller->AddTraceStateObserver(trace_state_observer_.get());
-    StartTracingAgent();
+    tracing_file_writer_ = tracing_agent_->DefaultHandle();
+    // Only start the tracing agent if we enabled any tracing categories.
+    if (!per_process::cli_options->trace_event_categories.empty()) {
+      StartTracingAgent();
+    }
     // Tracing must be initialized before platform threads are created.
     platform_ = new NodePlatform(thread_pool_size, controller);
     v8::V8::InitializePlatform(platform_);
@@ -111,9 +115,9 @@ struct V8Platform {
   }
 
   inline void StartTracingAgent() {
-    if (per_process::cli_options->trace_event_categories.empty()) {
-      tracing_file_writer_ = tracing_agent_->DefaultHandle();
-    } else {
+    // Attach a new NodeTraceWriter only if this function hasn't been called
+    // before.
+    if (tracing_file_writer_.IsDefaultHandle()) {
       std::vector<std::string> categories =
           SplitString(per_process::cli_options->trace_event_categories, ',');
 
@@ -163,6 +167,10 @@ namespace per_process {
 extern struct V8Platform v8_platform;
 }
 
+inline void StartTracingAgent() {
+  return per_process::v8_platform.StartTracingAgent();
+}
+
 inline tracing::AgentWriterHandle* GetTracingAgentWriter() {
   return per_process::v8_platform.GetTracingAgentWriter();
 }