Checking whether Fabric is enabled

[joemun]

👋 We are in the process of migrating our app to New Architecture, and we've hit a crash where Reanimated thinks it's running in old arch, specifically the code here where the _IS_FABRIC check is returning undefined. This code is being run on module load, so I do wonder if there's perhaps a race condition where this value has yet to be set. I do see that it's being set in RNRuntimeDecorator.cpp

Also, I'm curious what is the proper way of checking for fabric. RN Screens also checks for _IS_FABRIC, but RNGH checks for global.nativeFabricUIManager. The RNGH check is interesting because we had to patch on our end to change it from checking global?.nativeFabricUIManager to global._IS_FABRIC, as it was causing an intermittent crash for some users.

[tjzel]

Hi @joemun. We recently had a fix to _IS_FABRIC on UI thread #5143. Although it doesn't seem to be the case, could you see if it's fixed for you on our nightly version? yarn add react-native-reanimated@nightly.

[joemun]

@tjzel I'm sorry for the belated response. We are still hitting this issue. We just bumped to version 3.6.0-nightly-20231016-02551af17.

[tjzel]

@joemun I'm afraid without a reproduction I can't help you. Injection of e.g. _IS_FABRIC to both RN and UI threads is done synchronously so it's hard to have a race condition here. Feel free to open an issue with the reproduction.