From f9defa61fa95bcce4fa2e04b1204ca703d6604a2 Mon Sep 17 00:00:00 2001
From: Filip Skokan <panva.ip@gmail.com>
Date: Thu, 8 Oct 2026 11:58:29 +0200
Subject: [PATCH] lib: fix benchmark record acknowledgement race

The child can receive an acknowledgement and send its next record before
the parent's send callback runs. Clear recordPending before sending the
acknowledgement to avoid rejecting that record as an invalid sequence.

Add a regression test that delays send callbacks until the child sends
its next record or closes.

Signed-off-by: Filip Skokan <panva.ip@gmail.com>
Assisted-by: Codex
PR-URL: https://github.com/nodejs/node/pull/66430
Reviewed-By: James M Snell <jasnell@gmail.com>
---
 lib/internal/bench_runner/cli.js           |  7 ++---
 test/fixtures/bench-runner/delayed-ack.cjs | 31 ++++++++++++++++++++++
 test/parallel/test-bench-cli-ack.js        | 23 ++++++++++++++++
 3 files changed, 58 insertions(+), 3 deletions(-)
 create mode 100644 test/fixtures/bench-runner/delayed-ack.cjs
 create mode 100644 test/parallel/test-bench-cli-ack.js

diff --git a/lib/internal/bench_runner/cli.js b/lib/internal/bench_runner/cli.js
index 48af55c9cf1..5884046e146 100644
--- a/lib/internal/bench_runner/cli.js
+++ b/lib/internal/bench_runner/cli.js
@@ -956,10 +956,11 @@ async function runChild(path, options, scope, onRecord) {
         }
         const pending = handleRecord(record);
         if (protocolError === undefined) {
-          const acknowledged = PromisePrototypeThen(
-            PromiseResolve(pending), () => sendAck(child, message.id));
-          trackPending(PromisePrototypeThen(acknowledged, () => {
+          trackPending(PromisePrototypeThen(PromiseResolve(pending), () => {
+            // The child can receive the acknowledgement and send its next
+            // record before the send callback runs.
             recordPending = false;
+            return sendAck(child, message.id);
           }));
         }
       } catch (error) {
diff --git a/test/fixtures/bench-runner/delayed-ack.cjs b/test/fixtures/bench-runner/delayed-ack.cjs
new file mode 100644
index 00000000000..3d439aa579f
--- /dev/null
+++ b/test/fixtures/bench-runner/delayed-ack.cjs
@@ -0,0 +1,31 @@
+'use strict';
+
+const common = require('../../common');
+const childProcess = require('child_process');
+const { spawn } = childProcess;
+
+childProcess.spawn = (...args) => {
+  const child = spawn(...args);
+  const { send } = child;
+  child.send = function(message, handle, options, callback) {
+    if (message?.type === 'node:bench:ack') {
+      // Report send completion only after the child has responded to the ack.
+      const onComplete = common.mustCall(() => {
+        child.removeListener('message', onComplete);
+        child.removeListener('close', onComplete);
+        callback(null);
+      });
+      child.once('message', onComplete);
+      child.once('close', onComplete);
+      return send.call(this, message, handle, options, (error) => {
+        if (error) {
+          child.removeListener('message', onComplete);
+          child.removeListener('close', onComplete);
+          callback(error);
+        }
+      });
+    }
+    return send.call(this, message, handle, options, callback);
+  };
+  return child;
+};
diff --git a/test/parallel/test-bench-cli-ack.js b/test/parallel/test-bench-cli-ack.js
new file mode 100644
index 00000000000..99bf9b58b27
--- /dev/null
+++ b/test/parallel/test-bench-cli-ack.js
@@ -0,0 +1,23 @@
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+const { spawnSync } = require('child_process');
+const fixtures = require('../common/fixtures');
+
+const result = spawnSync(process.execPath, [
+  '--no-warnings', '--experimental-bench', '--bench',
+  '--require', fixtures.path('bench-runner/delayed-ack.cjs'),
+  '--bench-reporter=json',
+  fixtures.path('bench-runner/acknowledged-records.mjs'),
+], { encoding: 'utf8', timeout: common.platformTimeout(30_000) });
+
+assert.ifError(result.error);
+assert.strictEqual(result.signal, null);
+assert.strictEqual(result.status, 0, result.stdout + result.stderr);
+assert.strictEqual(result.stderr, '');
+const records = result.stdout.trim().split('\n').map((line) => JSON.parse(line));
+const diagnostics = records.filter(({ type }) => type === 'bench:diagnostic');
+assert.strictEqual(diagnostics.length, 32);
+assert(diagnostics.every(({ data }) => /^acknowledged 10\d{3}$/.test(data.message)));
+assert.strictEqual(records.at(-1).data.success, true);