From 0a51aa8fdb37771c5f5ee88e5b082ae3c1603d56 Mon Sep 17 00:00:00 2001
From: Gerhard Stoebich <18708370+Flarna@users.noreply.github.com>
Date: Mon, 3 Aug 2020 23:19:54 +0200
Subject: [PATCH] async_hooks: avoid unneeded AsyncResource creation

Inspired by the callstack at https://github.com/nodejs/node/issues/34556#issuecomment-666743528

If the wanted store is equal to the active store it's not needed to
create an AsyncResource.

Refs: https://github.com/nodejs/node/issues/34556#issuecomment-666743528

PR-URL: https://github.com/nodejs/node/pull/34616
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Stephen Belanger <admin@stephenbelanger.com>
Reviewed-By: Vladimir de Turckheim <vlad2t@hotmail.com>
Reviewed-By: Andrey Pechkurov <apechkurov@gmail.com>
---
 lib/async_hooks.js                              |  5 +++++
 .../test-async-local-storage-run-resource.js    | 17 +++++++++++++++--
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/lib/async_hooks.js b/lib/async_hooks.js
index 02362973ae1de6..758c4eab10fe83 100644
--- a/lib/async_hooks.js
+++ b/lib/async_hooks.js
@@ -3,6 +3,7 @@
 const {
   NumberIsSafeInteger,
   ObjectDefineProperties,
+  ObjectIs,
   ReflectApply,
   Symbol,
 } = primordials;
@@ -288,6 +289,10 @@ class AsyncLocalStorage {
   }
 
   run(store, callback, ...args) {
+    // Avoid creation of an AsyncResource if store is already active
+    if (ObjectIs(store, this.getStore())) {
+      return callback(...args);
+    }
     const resource = new AsyncResource('AsyncLocalStorage');
     return resource.runInAsyncScope(() => {
       this.enterWith(store);
diff --git a/test/async-hooks/test-async-local-storage-run-resource.js b/test/async-hooks/test-async-local-storage-run-resource.js
index 9a7479f699246c..21bc70051bd718 100644
--- a/test/async-hooks/test-async-local-storage-run-resource.js
+++ b/test/async-hooks/test-async-local-storage-run-resource.js
@@ -10,8 +10,21 @@ const asyncLocalStorage = new AsyncLocalStorage();
 
 const outerResource = executionAsyncResource();
 
-asyncLocalStorage.run(new Map(), () => {
-  assert.notStrictEqual(executionAsyncResource(), outerResource);
+const store = new Map();
+asyncLocalStorage.run(store, () => {
+  assert.strictEqual(asyncLocalStorage.getStore(), store);
+  const innerResource = executionAsyncResource();
+  assert.notStrictEqual(innerResource, outerResource);
+  asyncLocalStorage.run(store, () => {
+    assert.strictEqual(asyncLocalStorage.getStore(), store);
+    assert.strictEqual(executionAsyncResource(), innerResource);
+    const otherStore = new Map();
+    asyncLocalStorage.run(otherStore, () => {
+      assert.strictEqual(asyncLocalStorage.getStore(), otherStore);
+      assert.notStrictEqual(executionAsyncResource(), innerResource);
+      assert.notStrictEqual(executionAsyncResource(), outerResource);
+    });
+  });
 });
 
 assert.strictEqual(executionAsyncResource(), outerResource);