trace_events: adds a new trace_events api

Removes the requirement to use `--trace-events-enabled` to enable
trace events. Tracing is enabled automatically if there are any
enabled categories.

Adds a new `trace_events` module with an API for enabling/disabling
trace events at runtime without a command line flag.

```js
const trace_events = require('trace_events');
const categories = [ 'node.perf', 'node.async_hooks' ];
const tracing = trace_events.createTracing({ categories });
tracing.enable();
// do stuff
tracing.disable();
```

Multiple `Tracing` objects may exist and be enabled at any point
in time. The enabled trace event categories is the union of all
enabled `Tracing` objects and the `--trace-event-categories`
flag.

PR-URL: https://github.com/nodejs/node/pull/19803
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Ali Ijaz Sheikh <ofrobots@google.com>
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>

1 files changed, 18 insertions, 1 deletions

diff --git a/src/tracing/agent.h b/src/tracing/agent.h
index 9d6bc4e90a..ca5fd35417 100644
--- a/src/tracing/agent.h
+++ b/src/tracing/agent.h
@@ -5,9 +5,14 @@
 #include "uv.h"
 #include "v8.h"
 
+#include <set>
+#include <string>
+
 namespace node {
 namespace tracing {
 
+using v8::platform::tracing::TraceConfig;
+
 class TracingController : public v8::platform::tracing::TracingController {
  public:
   TracingController() : v8::platform::tracing::TracingController() {}
@@ -20,17 +25,29 @@ class TracingController : public v8::platform::tracing::TracingController {
 class Agent {
  public:
   explicit Agent(const std::string& log_file_pattern);
-  void Start(const std::string& enabled_categories);
   void Stop();
 
   TracingController* GetTracingController() { return tracing_controller_; }
 
+  void Enable(const std::string& categories);
+  void Enable(const std::set<std::string>& categories);
+  void Disable(const std::set<std::string>& categories);
+  std::string GetEnabledCategories();
+
  private:
   static void ThreadCb(void* arg);
 
+  void Start();
+  void RestartTracing();
+
+  TraceConfig* CreateTraceConfig();
+
+  const std::string& log_file_pattern_;
   uv_thread_t thread_;
   uv_loop_t tracing_loop_;
   bool started_ = false;
+
+  std::multiset<std::string> categories_;
   TracingController* tracing_controller_ = nullptr;
 };