process: simplify the setup of async hooks trace events

- Remove `trace_category_state` from `Environment` - since this is
  only accessed in the bootstrap process and later in the
  trace category update handler, we could just pass the initial
  values into JS land via the trace_events binding, and pass
  the dynamic values directly to the handler later, instead of
  accessing them out-of-band via the AliasedBuffer.
- Instead of creating the hooks directly in
  `trace_events_async_hooks.js`, export the hook factory and
  create the hooks in trace category state toggle.

PR-URL: https://github.com/nodejs/node/pull/26062
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/internal/bootstrap/pre_execution.js

@@ -1,6 +1,9 @@
 'use strict';
 
 const { getOptionValue } = require('internal/options');
+// Lazy load internal/trace_events_async_hooks only if the async_hooks
+// trace event category is enabled.
+let traceEventsAsyncHook;
 
 function prepareMainThreadExecution() {
   setupTraceCategoryState();
@@ -27,32 +30,27 @@ function prepareMainThreadExecution() {
 
 function setupTraceCategoryState() {
   const {
-    traceCategoryState,
+    asyncHooksEnabledInitial,
     setTraceCategoryStateUpdateHandler
   } = internalBinding('trace_events');
-  const kCategoryAsyncHooks = 0;
-  let traceEventsAsyncHook;
 
-  function toggleTraceCategoryState() {
-    // Dynamically enable/disable the traceEventsAsyncHook
-    const asyncHooksEnabled = !!traceCategoryState[kCategoryAsyncHooks];
-
-    if (asyncHooksEnabled) {
-      // Lazy load internal/trace_events_async_hooks only if the async_hooks
-      // trace event category is enabled.
-      if (!traceEventsAsyncHook) {
-        traceEventsAsyncHook = require('internal/trace_events_async_hooks');
-      }
-      traceEventsAsyncHook.enable();
-    } else if (traceEventsAsyncHook) {
-      traceEventsAsyncHook.disable();
-    }
-  }
-
-  toggleTraceCategoryState();
+  toggleTraceCategoryState(asyncHooksEnabledInitial);
   setTraceCategoryStateUpdateHandler(toggleTraceCategoryState);
 }
 
+// Dynamically enable/disable the traceEventsAsyncHook
+function toggleTraceCategoryState(asyncHooksEnabled) {
+  if (asyncHooksEnabled) {
+    if (!traceEventsAsyncHook) {
+      traceEventsAsyncHook =
+        require('internal/trace_events_async_hooks').createHook();
+    }
+    traceEventsAsyncHook.enable();
+  } else if (traceEventsAsyncHook) {
+    traceEventsAsyncHook.disable();
+  }
+}
+
 // In general deprecations are intialized wherever the APIs are implemented,
 // this is used to deprecate APIs implemented in C++ where the deprecation
 // utitlities are not easily accessible.

lib/internal/trace_events_async_hooks.js

@@ -83,4 +83,4 @@ function createHook() {
   };
 }
 
-module.exports = createHook();
+exports.createHook = createHook;

src/env-inl.h

@@ -455,11 +455,6 @@ Environment::should_abort_on_uncaught_toggle() {
   return should_abort_on_uncaught_toggle_;
 }
 
-inline AliasedBuffer<uint8_t, v8::Uint8Array>&
-Environment::trace_category_state() {
-  return trace_category_state_;
-}
-
 inline AliasedBuffer<int32_t, v8::Int32Array>&
 Environment::stream_base_state() {
   return stream_base_state_;

src/env.cc

@@ -21,6 +21,7 @@
 namespace node {
 
 using errors::TryCatchScope;
+using v8::Boolean;
 using v8::Context;
 using v8::EmbedderGraph;
 using v8::External;
@@ -152,9 +153,8 @@ void Environment::TrackingTraceStateObserver::UpdateTraceCategoryState() {
     return;
   }
 
-  env_->trace_category_state()[0] =
-      *TRACE_EVENT_API_GET_CATEGORY_GROUP_ENABLED(
-          TRACING_CATEGORY_NODE1(async_hooks));
+  bool async_hooks_enabled = (*(TRACE_EVENT_API_GET_CATEGORY_GROUP_ENABLED(
+                                 TRACING_CATEGORY_NODE1(async_hooks)))) != 0;
 
   Isolate* isolate = env_->isolate();
   HandleScope handle_scope(isolate);
@@ -163,8 +163,9 @@ void Environment::TrackingTraceStateObserver::UpdateTraceCategoryState() {
     return;
   TryCatchScope try_catch(env_);
   try_catch.SetVerbose(true);
-  cb->Call(env_->context(), Undefined(isolate),
-           0, nullptr).ToLocalChecked();
+  Local<Value> args[] = {Boolean::New(isolate, async_hooks_enabled)};
+  cb->Call(env_->context(), Undefined(isolate), arraysize(args), args)
+      .ToLocalChecked();
 }
 
 static std::atomic<uint64_t> next_thread_id{0};
@@ -183,7 +184,6 @@ Environment::Environment(IsolateData* isolate_data,
       tick_info_(context->GetIsolate()),
       timer_base_(uv_now(isolate_data->event_loop())),
       should_abort_on_uncaught_toggle_(isolate_, 1),
-      trace_category_state_(isolate_, kTraceCategoryCount),
       stream_base_state_(isolate_, StreamBase::kNumStreamBaseStateFields),
       flags_(flags),
       thread_id_(thread_id == kNoThreadId ? AllocateThreadId() : thread_id),

src/env.h

@@ -707,7 +707,6 @@ class Environment {
   inline AliasedBuffer<uint32_t, v8::Uint32Array>&
   should_abort_on_uncaught_toggle();
 
-  inline AliasedBuffer<uint8_t, v8::Uint8Array>& trace_category_state();
   inline AliasedBuffer<int32_t, v8::Int32Array>& stream_base_state();
 
   // The necessary API for async_hooks.
@@ -1022,8 +1021,6 @@ class Environment {
   AliasedBuffer<uint32_t, v8::Uint32Array> should_abort_on_uncaught_toggle_;
   int should_not_abort_scope_counter_ = 0;
 
-  // Attached to a Uint8Array that tracks the state of trace category
-  AliasedBuffer<uint8_t, v8::Uint8Array> trace_category_state_;
   std::unique_ptr<TrackingTraceStateObserver> trace_state_observer_;
 
   AliasedBuffer<int32_t, v8::Int32Array> stream_base_state_;

src/node_trace_events.cc

@@ -1,6 +1,7 @@
 #include "base_object-inl.h"
 #include "env.h"
 #include "node.h"
+#include "node_internals.h"
 #include "node_v8_platform-inl.h"
 #include "tracing/agent.h"
 
@@ -10,6 +11,7 @@
 namespace node {
 
 using v8::Array;
+using v8::Boolean;
 using v8::Context;
 using v8::Function;
 using v8::FunctionCallbackInfo;
@@ -148,9 +150,14 @@ void NodeCategorySet::Initialize(Local<Object> target,
   target->Set(context, trace,
               binding->Get(context, trace).ToLocalChecked()).FromJust();
 
-  target->Set(context,
-              FIXED_ONE_BYTE_STRING(env->isolate(), "traceCategoryState"),
-              env->trace_category_state().GetJSArray()).FromJust();
+  // Initial value of async hook trace events
+  bool async_hooks_enabled = (*(TRACE_EVENT_API_GET_CATEGORY_GROUP_ENABLED(
+                                 TRACING_CATEGORY_NODE1(async_hooks)))) != 0;
+  target
+      ->Set(context,
+            FIXED_ONE_BYTE_STRING(env->isolate(), "asyncHooksEnabledInitial"),
+            Boolean::New(env->isolate(), async_hooks_enabled))
+      .FromJust();
 }
 
 }  // namespace node