From f59f41f6fcd6675b013f739200747bbdda67a247 Mon Sep 17 00:00:00 2001
From: Joyee Cheung <joyeec9h3@gmail.com>
Date: Fri, 1 Feb 2019 01:04:44 +0800
Subject: [PATCH] perf_hooks: only enable GC tracking when it's requested

Previously a GC prologue callback and a GC epilogue callback
are always unconditionally enabled during bootstrap when
the `performance` binding is loaded, even when the user does
not use the performance timeline API to enable GC tracking.
This patch makes the callback addition conditional and only
enables them when the user explicitly requests
`observer.observe(['gc'])` to avoid the overhead.
---
 lib/perf_hooks.js | 10 +++++++++-
 src/node_perf.cc  |  8 +++++---
 2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/lib/perf_hooks.js b/lib/perf_hooks.js
index cb1640ef9bd679..583ffb56cae5e3 100644
--- a/lib/perf_hooks.js
+++ b/lib/perf_hooks.js
@@ -11,7 +11,8 @@ const {
   timeOrigin,
   timeOriginTimestamp,
   timerify,
-  constants
+  constants,
+  setupGarbageCollectionTracking
 } = internalBinding('performance');
 
 const {
@@ -273,6 +274,8 @@ class PerformanceObserverEntryList {
   }
 }
 
+let gcTrackingIsEnabled = false;
+
 class PerformanceObserver extends AsyncResource {
   constructor(callback) {
     if (typeof callback !== 'function') {
@@ -334,6 +337,11 @@ class PerformanceObserver extends AsyncResource {
     if (entryTypes.length === 0) {
       throw new errors.ERR_VALID_PERFORMANCE_ENTRY_TYPE();
     }
+    if (entryTypes.includes(NODE_PERFORMANCE_ENTRY_TYPE_GC) &&
+      !gcTrackingIsEnabled) {
+      setupGarbageCollectionTracking();
+      gcTrackingIsEnabled = true;
+    }
     this.disconnect();
     this[kBuffer][kEntries] = [];
     L.init(this[kBuffer][kEntries]);
diff --git a/src/node_perf.cc b/src/node_perf.cc
index cefd0ff26dbf95..33dd1d2051872c 100644
--- a/src/node_perf.cc
+++ b/src/node_perf.cc
@@ -296,8 +296,10 @@ void MarkGarbageCollectionEnd(Isolate* isolate,
                          entry);
 }
 
+static void SetupGarbageCollectionTracking(
+    const FunctionCallbackInfo<Value>& args) {
+  Environment* env = Environment::GetCurrent(args);
 
-inline void SetupGarbageCollectionTracking(Environment* env) {
   env->isolate()->AddGCPrologueCallback(MarkGarbageCollectionStart,
                                         static_cast<void*>(env));
   env->isolate()->AddGCEpilogueCallback(MarkGarbageCollectionEnd,
@@ -416,6 +418,8 @@ void Initialize(Local<Object> target,
   env->SetMethod(target, "markMilestone", MarkMilestone);
   env->SetMethod(target, "setupObservers", SetupPerformanceObservers);
   env->SetMethod(target, "timerify", Timerify);
+  env->SetMethod(
+      target, "setupGarbageCollectionTracking", SetupGarbageCollectionTracking);
 
   Local<Object> constants = Object::New(isolate);
 
@@ -452,8 +456,6 @@ void Initialize(Local<Object> target,
                             env->constants_string(),
                             constants,
                             attr).ToChecked();
-
-  SetupGarbageCollectionTracking(env);
 }
 
 }  // namespace performance