From 1becba6284bdb3edb6bb7af8e2efbcaca69455e4 Mon Sep 17 00:00:00 2001
From: Filip Skokan <panva.ip@gmail.com>
Date: Thu, 1 Oct 2026 11:39:46 +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
---
 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 96930ca56878..cf53d6360011 100644
--- a/lib/internal/bench_runner/cli.js
+++ b/lib/internal/bench_runner/cli.js
@@ -954,10 +954,11 @@ 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 000000000000..3d439aa579fc
--- /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 000000000000..99bf9b58b27c
--- /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);