fix(babel-register): preserve app-managed graceful shutdown by jibin7jose · Pull Request #18137 · babel/babel

jibin7jose · 2026-07-17T04:16:50Z

Description:
This PR addresses an issue where @babel/register forces an early process.exit(0) when receiving SIGTERM or SIGINT signals, which inadvertently interrupts any application-managed graceful shutdown routines.

Changes:

Updated the signal listener in packages/babel-register/src/index.ts to check process.listenerCount(signal).
If @babel/register is the only listener, it removes itself and re-raises the signal using process.kill() to preserve default Node.js termination behavior.
If there are other listeners present, it simply cleans up its worker client and avoids forcing process.exit(0), allowing the rest of the application's shutdown handlers to run naturally.

babel-bot · 2026-07-17T04:18:53Z

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/61948

pkg-pr-new · 2026-07-17T04:47:41Z

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commit: 246e809

JLHwung · 2026-07-17T14:35:04Z

Thank you. Recently we have added a test framework for -r @babel/register in #18131, could you rebase on the main and add a new test for the change?

jibin7jose · 2026-07-17T16:34:05Z

@JLHwung Thanks for the review!

I've rebased the branch on top of main and added a new test for the graceful shutdown behavior in packages/babel-register/test/fixtures/preload/--require/graceful-shutdown using the new test framework as requested.

However, it looks like the CI is having some infrastructure issues:

One of the jobs threw a 403 Forbidden error with actions/download-artifact (likely a fork PR permission issue).
The test262 (4) shard failed after 50 minutes (likely a flaky timeout or related to the artifact download issue).
Could you take a look or re-run the failed jobs when you have a moment? Let me know if there's anything else you need me to change on my end!

JLHwung

Thank you. This PR does reveal a question that we never think about before:

Does user expect @babel/register to still work in the shutdown listener?

Currently when @babel/register is preloaded, the babel-register listener is very likely the first registered listener and thus executed earlier than any other user-defined listeners. At the point when user-defined listener runs, @babel/register has already reverted, so any require to other files will not be transpiled.

If @babel/register should be the last listener being removed, we should run the whole client teardown logic only when the listenerCount is 1, though if a user-defined listener does not de-register itself, the @babel/register will never get a chance to be removed.

@nicolo-ribaudo @liuxingbaoyu WDYT?

JLHwung · 2026-07-17T16:47:14Z

-        // eslint-disable-next-line n/no-process-exit
-        process.exit(0);
+        if (process.listenerCount(signalOrCode) === 1) {
+          process.off(signalOrCode, listener!);


We should remove listeners for the other two signals as well, because at this point the client has been closed and re-entry to the listener via a different signal will exit early but we didn't get a chance to remove the listener for that signal.

JLHwung · 2026-07-17T16:55:57Z

@JLHwung Thanks for the review!

I've rebased the branch on top of main and added a new test for the graceful shutdown behavior in packages/babel-register/test/fixtures/preload/--require/graceful-shutdown using the new test framework as requested.

However, it looks like the CI is having some infrastructure issues:

One of the jobs threw a 403 Forbidden error with actions/download-artifact (likely a fork PR permission issue). The test262 (4) shard failed after 50 minutes (likely a flaky timeout or related to the artifact download issue). Could you take a look or re-run the failed jobs when you have a moment? Let me know if there's anything else you need me to change on my end!

Thanks, the CI error is probably not related. You can naturally retry the CI after addressing my review comments above.

jibin7jose · 2026-07-17T17:03:15Z

@JLHwung Thanks for the explanation! I've updated the shutdown logic to cleanly remove the listeners for exit, SIGINT, and SIGTERM as you suggested.

liuxingbaoyu · 2026-07-18T06:06:43Z

@JLHwung
Is listening exit enough?
Uninstalling the hook might not be very important, as long as we save the cache correctly.

JLHwung · 2026-07-20T13:54:17Z

@JLHwung Is listening exit enough?

No. Per Node.js docs https://nodejs.org/api/process.html#process_event_exit, the exit event will be fired when

The process.exit() method being called explicitly;
The Node.js event loop no longer having any additional work to perform.

The default SIGINT handler does not fire the exit event: nodejs/node#2853.

Uninstalling the hook might not be very important, as long as we save the cache correctly.

The timing of hook uninstalling does yield observable behaviour differences: The current behaviour is any user-land exit listener will not be run with babel-register, because at the moment when they run, babel-register has been uninstalled.

liuxingbaoyu · 2026-07-20T16:49:56Z

Oops, I realize we didn't actually uninstall the hook, it just saved the cache.
I pushed a commit to reflect this.

liuxingbaoyu · 2026-07-20T16:52:01Z

This PR also fixes another issue: previously, the SIGINT signal would always cause the program to exit, but now users can catch it without exiting.
Thanks! @jibin7jose

nicolo-ribaudo · 2026-08-07T13:46:05Z

Looking at the code I cannot figure out where in the listener we would be uninstalling @babel/register, was that about an older version of the patch and now it's not happening anymore?

liuxingbaoyu · 2026-08-07T14:15:20Z

In the past, we thought that @babel/register would be unloaded when exit was called, but we later found that we never automatically called revert, and ACTIONS.CLOSE only saved the cache.
Since that's the case, the original behavior doesn't need to be changed.

nicolo-ribaudo · 2026-08-07T14:19:53Z

Thanks!

jibin7jose · 2026-08-07T14:50:58Z

Hi @nicolo-ribaudo — thank you for reviewing and merging the PR. Since the core fix and implementation originated from my contribution in this PR, I’d like to be formally credited as a co-author.
Could you please add the following line to the commit message?
Co-authored-by: Jibin Jose [email protected]
This will ensure my contribution is properly attributed to my GitHub profile and contribution history. Thank you!

nicolo-ribaudo · 2026-08-07T14:54:02Z

You are already credited as the main author of the commit: https://github.com/babel/babel/commit/36057c706ce82a0d0a1c8a5f7721e6fcae4ab1b6.patch

jibin7jose · 2026-08-07T14:55:19Z

Thanks

jibin7jose added 3 commits July 17, 2026 20:50

fix(babel-register): preserve app-managed graceful shutdown

c70cb9d

chore(babel-register): fix typescript type error

9b9cc7b

test(babel-register): add graceful shutdown test

b80ff22

jibin7jose force-pushed the fix-babel-register-graceful-shutdown branch from 6edcf71 to b80ff22 Compare July 17, 2026 15:25

JLHwung approved these changes Jul 17, 2026

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fix(babel-register): remove all listeners on shutdown

e26424e

improve

246e809

liuxingbaoyu added PR: Bug Fix 🐛 A type of pull request used for our changelog categories pkg: register labels Jul 20, 2026

harshmathurx mentioned this pull request Aug 5, 2026

fix(register): preserve app signal shutdown handlers #18170

Closed

liuxingbaoyu requested a review from nicolo-ribaudo August 7, 2026 13:28

nicolo-ribaudo approved these changes Aug 7, 2026

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nicolo-ribaudo merged commit 36057c7 into babel:main Aug 7, 2026
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