src: refactor tracing agent code

Avoid unnecessary operations, add a bit of documentation,
and turn the `ClientHandle` smart pointer alias into a real
class.

This should allow de-coupling the unnecessary combination of
a single specific `file_writer` from `Agent`.

PR-URL: https://github.com/nodejs/node/pull/21867
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Eugene Ostroukhov <eostroukhov@google.com>
Reviewed-By: Ali Ijaz Sheikh <ofrobots@google.com>

2 files changed, 4 insertions, 10 deletions

diff --git a/src/inspector/tracing_agent.cc b/src/inspector/tracing_agent.cc
index c0425aab29..92c3597590 100644
--- a/src/inspector/tracing_agent.cc
+++ b/src/inspector/tracing_agent.cc
@@ -46,9 +46,7 @@ class InspectorTraceWriter : public node::tracing::AsyncTraceWriter {
 }  // namespace
 
 TracingAgent::TracingAgent(Environment* env)
-                           : env_(env),
-                             trace_writer_(
-                                  tracing::Agent::EmptyClientHandle()) {
+                           : env_(env) {
 }
 
 TracingAgent::~TracingAgent() {
@@ -62,7 +60,7 @@ void TracingAgent::Wire(UberDispatcher* dispatcher) {
 
 DispatchResponse TracingAgent::start(
     std::unique_ptr<protocol::NodeTracing::TraceConfig> traceConfig) {
-  if (trace_writer_ != nullptr) {
+  if (!trace_writer_.empty()) {
     return DispatchResponse::Error(
         "Call NodeTracing::end to stop tracing before updating the config");
   }
diff --git a/src/inspector/tracing_agent.h b/src/inspector/tracing_agent.h
index 478107c5ac..029fce7c19 100644
--- a/src/inspector/tracing_agent.h
+++ b/src/inspector/tracing_agent.h
@@ -2,16 +2,13 @@
 #define SRC_INSPECTOR_TRACING_AGENT_H_
 
 #include "node/inspector/protocol/NodeTracing.h"
+#include "tracing/agent.h"
 #include "v8.h"
 
 
 namespace node {
 class Environment;
 
-namespace tracing {
-class Agent;
-}  // namespace tracing
-
 namespace inspector {
 namespace protocol {
 
@@ -32,8 +29,7 @@ class TracingAgent : public NodeTracing::Backend {
   void DisconnectTraceClient();
 
   Environment* env_;
-  std::unique_ptr<std::pair<tracing::Agent*, int>,
-                  void (*)(std::pair<tracing::Agent*, int>*)> trace_writer_;
+  tracing::AgentWriterHandle trace_writer_;
   std::unique_ptr<NodeTracing::Frontend> frontend_;
 };