JS thread stalls while using Hermes with iOS on RN 0.68.3

[jkepps]

Bug Description

Similarly to this issue, I'm attempting to enable hermes on my react native app, but when I do so, the iOS (iPhone 14 Pro simulator) app freezes for minutes (10-20+ min) with no errors, crashes, or logs of any kind. I've done some profiling as suggested in the issue reference above, and here is the output.

The nested objects with the highest % of Retained size all cause the Allocation stack section to display "Stack was not recorded for this object because it had been allocated before this profiling recording started."

• I have run gradle clean and confirmed this bug does not occur with JSC

Hermes version: unsure
React Native version (if any): 0.68.3
OS version (if any): iOS 16
Platform (most likely one of arm64-v8a, armeabi-v7a, x86, x86_64): unsure

[jpporto]

Hi,

Thank you for reporting this. Can you provide a repro? Otherwise it won't be possible to debug what's going on.

John Paulo

[jkepps]

@jpporto thanks for the quick reply. turns out i wasn't polyfilling the Intl module correctly so the js thread was grinding to a halt while trying to parse some dates shortly after rendering the home screen. I was also on a really old version of Luxon (v1), so I wasn't getting the typical error that most others get when they forget to polyfill 🫠. This is ultimately what helped me, in case anyone else stumbles upon this same problem.