util: optimize promise introspection

Use V8's builtin ObjectIsPromise() to check that the value is a promise before creating the promise mirror. Reduces garbage collector strain in the (common) non-promise case, which is beneficial when inspecting deep object graphs. PR-URL: #3130 Reviewed-By: Evan Lucas <[email protected]> Reviewed-By: Sakthipriyan Vairamani <[email protected]>
nodejs · Oct 2, 2015 · d8ab4e1 · d8ab4e1
1 parent a0b35bf
commit d8ab4e1
Showing 1 changed file with 15 additions and 3 deletions.
diff --git a/lib/util.js b/lib/util.js
@@ -3,7 +3,9 @@
 const uv = process.binding('uv');
 const Buffer = require('buffer').Buffer;
 const internalUtil = require('internal/util');
+
 var Debug;
+var ObjectIsPromise;
 
 const formatRegExp = /%[sdj%]/g;
 exports.format = function(f) {
@@ -183,11 +185,21 @@ function getConstructorOf(obj) {
 }
 
 
+function ensureDebugIsInitialized() {
+  if (Debug === undefined) {
+    const runInDebugContext = require('vm').runInDebugContext;
+    const result = runInDebugContext('[Debug, ObjectIsPromise]');
+    Debug = result[0];
+    ObjectIsPromise = result[1];
+  }
+}
+
+
 function inspectPromise(p) {
-  Debug = Debug || require('vm').runInDebugContext('Debug');
-  var mirror = Debug.MakeMirror(p, true);
-  if (!mirror.isPromise())
+  ensureDebugIsInitialized();
+  if (!ObjectIsPromise(p))
     return null;
+  const mirror = Debug.MakeMirror(p, true);
   return {status: mirror.status(), value: mirror.promiseValue().value_};
 }