async_hooks: lazy loading for startup performance

PR-URL: #20567
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>

lib/internal/inspector_async_hook.js

@@ -1,49 +1,56 @@
 'use strict';
 
-const { createHook } = require('async_hooks');
 const inspector = process.binding('inspector');
-const config = process.binding('config');
 
 if (!inspector || !inspector.asyncTaskScheduled) {
   exports.setup = function() {};
   return;
 }
 
-const hook = createHook({
-  init(asyncId, type, triggerAsyncId, resource) {
+let hook;
+let config;
+
+function lazyHookCreation() {
+  const { createHook } = require('async_hooks');
+  config = process.binding('config');
+
+  hook = createHook({
+    init(asyncId, type, triggerAsyncId, resource) {
     // It's difficult to tell which tasks will be recurring and which won't,
     // therefore we mark all tasks as recurring. Based on the discussion
     // in https://github.com/nodejs/node/pull/13870#discussion_r124515293,
     // this should be fine as long as we call asyncTaskCanceled() too.
-    const recurring = true;
-    if (type === 'PROMISE')
-      this.promiseIds.add(asyncId);
-    else
-      inspector.asyncTaskScheduled(type, asyncId, recurring);
-  },
+      const recurring = true;
+      if (type === 'PROMISE')
+        this.promiseIds.add(asyncId);
+      else
+        inspector.asyncTaskScheduled(type, asyncId, recurring);
+    },
 
-  before(asyncId) {
-    if (this.promiseIds.has(asyncId))
-      return;
-    inspector.asyncTaskStarted(asyncId);
-  },
+    before(asyncId) {
+      if (this.promiseIds.has(asyncId))
+        return;
+      inspector.asyncTaskStarted(asyncId);
+    },
 
-  after(asyncId) {
-    if (this.promiseIds.has(asyncId))
-      return;
-    inspector.asyncTaskFinished(asyncId);
-  },
+    after(asyncId) {
+      if (this.promiseIds.has(asyncId))
+        return;
+      inspector.asyncTaskFinished(asyncId);
+    },
 
-  destroy(asyncId) {
-    if (this.promiseIds.has(asyncId))
-      return this.promiseIds.delete(asyncId);
-    inspector.asyncTaskCanceled(asyncId);
-  },
-});
+    destroy(asyncId) {
+      if (this.promiseIds.has(asyncId))
+        return this.promiseIds.delete(asyncId);
+      inspector.asyncTaskCanceled(asyncId);
+    },
+  });
 
-hook.promiseIds = new Set();
+  hook.promiseIds = new Set();
+}
 
 function enable() {
+  if (hook === undefined) lazyHookCreation();
   if (config.bits < 64) {
     // V8 Inspector stores task ids as (void*) pointers.
     // async_hooks store ids as 64bit numbers.
@@ -61,6 +68,7 @@ function enable() {
 }
 
 function disable() {
+  if (hook === undefined) lazyHookCreation();
   hook.disable();
 }