From 5ef225853c0f81ba0a7d1ce888ab3b2d283eae0a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bartek=20Iwa=C5=84czuk?= <biwanczuk@gmail.com>
Date: Wed, 14 Jun 2023 16:21:06 +0200
Subject: perf: don't run microtask checkpoint if macrotask callback did no
 work (#19492)

Most of the time there's no firing timers, nor pending promise
rejections, so it's wasteful to run microtask checkpoint
additionally twice on each tick of the event loop.

Closes https://github.com/denoland/deno/issues/18871
Ref https://github.com/denoland/deno/issues/19451
---
 core/01_core.js | 9 +++++++++
 1 file changed, 9 insertions(+)

(limited to 'core')

diff --git a/core/01_core.js b/core/01_core.js
index 13aa17c7e..d4a6508cb 100644
--- a/core/01_core.js
+++ b/core/01_core.js
@@ -187,7 +187,16 @@
       const cb = macrotaskCallbacks[i];
       while (true) {
         const res = cb();
+
+        // If callback returned `undefined` then it has no work to do, we don't
+        // need to perform microtask checkpoint.
+        if (res === undefined) {
+          break;
+        }
+
         ops.op_run_microtasks();
+        // If callback returned `true` then it has no more work to do, stop
+        // calling it then.
         if (res === true) {
           break;
         }
-- 
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