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cluster: report EADDRINUSE when a worker listens twice on the same port #65020

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cluster: report EADDRINUSE when a worker listens twice on the same port #65020

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ed8f6a3
cluster: report EADDRINUSE when a worker listens twice on the same port
islandryu Aug 4, 2026
d095f6e
test: cover SCHED_NONE and SCHED_RR in cluster listen-twice-same-port…
islandryu Aug 23, 2026
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12 changes: 11 additions & 1 deletion lib/internal/cluster/primary.js
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Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,7 @@ const {
} = require('internal/errors');

const assert = require('internal/assert');
const { UV_EADDRINUSE } = internalBinding('uv');
const { fork } = require('child_process');
const path = require('path');
const EventEmitter = require('events');
Expand Down Expand Up @@ -274,7 +275,16 @@ function queryServer(worker, message) {
`${message.fd}` + (message.port === 0 ? `:${message.index}` : '');
const cachedHandle = handles.get(key);
let handle;
if (cachedHandle && !cachedHandle.has(worker)) {
if (cachedHandle) {
if (cachedHandle.has(worker)) {
send(worker, {
errno: UV_EADDRINUSE,
key,
ack: message.seq,
data: cachedHandle.data,
});
return;
}
handle = cachedHandle;
}

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29 changes: 29 additions & 0 deletions test/sequential/test-cluster-listen-twice-same-port.js
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Original file line number Diff line number Diff line change
@@ -0,0 +1,29 @@
'use strict';

const common = require('../common');
const assert = require('assert');
const cluster = require('cluster');
const net = require('net');

@PickBas PickBas Aug 10, 2026

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I have a suggestion for the test: it passes on an unpatched build under SCHED_RR (the POSIX default), so it wouldn't catch a regression on Linux/macOS. The PR fixes behavior with SCHED_NONE, so could the tests cover both SCHED_RR and SCHED_NONE policies regardless of the OS?

@islandryu islandryu Aug 23, 2026

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Good catch! I've covered both policies.

if (cluster.isPrimary) {
cluster.fork().on('exit', common.mustCall((code) => {
assert.strictEqual(code, 0);
}));
return;
}

function listen() {
return new Promise((resolve, reject) => {
const server = net.createServer();
server.once('error', reject);
server.once('listening', () => resolve(server));
server.listen({ host: '127.0.0.1', port: common.PORT });
});
}

(async () => {
const server1 = await listen();
await assert.rejects(listen(), { code: 'EADDRINUSE' });
await new Promise((resolve) => server1.close(resolve));
cluster.worker.disconnect();
})().then(common.mustCall());
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