Periodic failures with parallel/test-child-process-stdout-flush-exit

[grahamc]

Test

parallel/test-child-process-stdout-flush-exit

Platform

Linux ARM64

Console output

2026-01-15T19:40:03.5158785Z     not ok 572 parallel/test-child-process-stdout-flush-exit
2026-01-15T19:40:03.5158846Z       ---
2026-01-15T19:40:03.5159008Z       duration_ms: 418.60800
2026-01-15T19:40:03.5159093Z       severity: fail
2026-01-15T19:40:03.5159158Z       exitcode: 1
2026-01-15T19:40:03.5159224Z       stack: |-
2026-01-15T19:40:03.5159287Z         node:assert:90
2026-01-15T19:40:03.5159370Z           throw new AssertionError(obj);
2026-01-15T19:40:03.5159426Z           ^
2026-01-15T19:40:03.5159799Z         
2026-01-15T19:40:03.5160025Z         AssertionError [ERR_ASSERTION]: Expected values to be strictly equal:
2026-01-15T19:40:03.5160103Z         + actual - expected
2026-01-15T19:40:03.5160161Z         
2026-01-15T19:40:03.5160227Z         + '\nfiller\n'
2026-01-15T19:40:03.5160288Z         - 'goodbye\n'
2026-01-15T19:40:03.5160616Z             at ChildProcess.<anonymous> (/build/node-v20.19.6/test/parallel/test-child-process-stdout-flush-exit.js:54:12)
2026-01-15T19:40:03.5160814Z             at ChildProcess.<anonymous> (/build/node-v20.19.6/test/common/index.js:474:15)
2026-01-15T19:40:03.5160926Z             at ChildProcess.emit (node:events:524:28)
2026-01-15T19:40:03.5161053Z             at maybeClose (node:internal/child_process:1104:16)
2026-01-15T19:40:03.5161228Z             at ChildProcess._handle.onexit (node:internal/child_process:304:5) {
2026-01-15T19:40:03.5161308Z           generatedMessage: true,
2026-01-15T19:40:03.5161380Z           code: 'ERR_ASSERTION',
2026-01-15T19:40:03.5161452Z           actual: '\nfiller\n',
2026-01-15T19:40:03.5161523Z           expected: 'goodbye\n',
2026-01-15T19:40:03.5161601Z           operator: 'strictEqual'
2026-01-15T19:40:03.5161658Z         }
2026-01-15T19:40:03.5161717Z         
2026-01-15T19:40:03.5161783Z         Node.js v20.19.6

Build links

• (none public, sorry)

Additional information

I'm not sure if this is the right place to report this. However, we ran into this flaky test when building Node on a machine with a high core count and a lot of other compilation jobs happening.

[LocutusOfBorg]

Hello, I see this at least on amd64 on Ubuntu 26.04 (20.19.4)
And I also have logs:
https://autopkgtest.ubuntu.com/results/autopkgtest-resolute/resolute/amd64/n/nodejs/20260115_194106_96c3b@/log.gz

[Han5991]

This flaky issue was inadvertently fixed by PR #62020 (specifically commit f951acf).

The root cause was the explicit process.exit(0) call. Under high load, when the stdout pipe buffer gets full, console.log('goodbye') becomes asynchronous. The immediate process.exit(0) forced the process to terminate before the event loop could flush the remaining buffer, cutting off the output.

Since PR #62020 removed that unnecessary process.exit(0), the process now naturally waits for the I/O event loop to drain, so this race condition will no longer occur. I believe this issue can be safely closed.