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--watch mode disables IPC communication between a spawning process and the actual child process #50880
Description
Activity
Ok, it turns out the fix is extremely simple, I'm happy to open a PR for this, I'm just not sure how to go about testing it. I think it's probably fine to require the parent process filter out unrelated (e.g., messages with
watch:prefixed keys) IPC messages.in 'lib/internal/files_watcher.js', add:
#setupIPC(child) { process.on("message", message => child.send(message)); child.on("message", message => process.send(message)); }then modify
constructorto have:#wantsPassthroughIPC = false; constructor({ throttle = 500, mode = 'filter' } = kEmptyObject) { super(); this.#wantsPassthroughIPC = !!process.send;then modify
watchChildProcessModulesto have:watchChildProcessModules(child, key = null) { if (this.#wantsPassthroughIPC) { this.#setupIPC(child); }Sound like a great solution,
for testing I would just add an extra case to https://github.com/nodejs/node/blob/main/test/sequential/test-watch-mode.mjs
with a fixture printing messages, validating it receives messages- added 2 commits that reference this issue
on Nov 24, 2023
Version
v18.17.1
Platform
Linux zacknewsham-xps 6.2.0-33-generic #33~22.04.1-Ubuntu SMP PREEMPT_DYNAMIC Thu Sep 7 10:33:52 UTC 2 x86_64 x86_64 x86_64 GNU/Linux
Subsystem
No response
What steps will reproduce the bug?
This isn't quite a bug, nor is it quite a feature request, but somewhere in between when using watch mode.
in
parent.jsin
child.jsHow often does it reproduce? Is there a required condition?
Always
What is the expected behavior? Why is that the expected behavior?
I expect to be able to communicate with a spawned child process, even when using
--watch.What do you see instead?
Because the
--watchmode uses IPC itself (to listen to messages from the child process) it doesn't pass through messages from the child to the parent, or the parent to the child.Additional information
As I said, this isn't quite a bug - but not quite a feature request either. I believe the fix is relatively simple, if the process has IPC enabled, then pass through messages (that aren't watch related) from the child -> parent and all messages from parent -> child