Fix database open failing consistently when reloading the app through the dev menu on Android.

[lachenmayer]

Hi there, thanks so much for this module! We're finding this super useful so far, really great to have a working leveldown implementation for React Native.

I discovered a slight rough edge in the Android bindings: it's not possible to open a database once the app has been reloaded using the dev menu.

To reproduce

1. open a database.
2. Reload the app using the dev menu.
3. open the database again (in our case, this is happening automatically on app startup.)

Expected

The database opens as usual.

Actual

The following error is thrown:

Possible Unhandled Promise Rejection (id: 0):
[OpenError: Error opening database cache: com.github.hf.leveldb.exception.LevelDBIOException: IO error: lock /data/user/0/chat.picnic.app.dev/files/cache.db/LOCK: already held by process]

Strangely, it's not possible to catch this error by wrapping open in try/catch. I still need to investigate why that is the case, but I thought it'd be better to fix this first.

Solution

onHostDestroy is a lifecycle event for the ReactRootView activity. We currently close all resources in this method. However, this does not get called when the dev menu reload happens, as the actual root view activity does not get destroyed. Instead, we use the onCatalystInstanceDestroy() method to trigger this close.

In classic React Native style, this isn't documented anywhere, and it took me ages to find out how to intercept this reload event. See facebook/react-native#9773 for similar frustrations. Linked from this I found invertase/react-native-firebase#1535, which implements the same solution.

Hope this makes sense, let me know if there's anything you need me to do to get this released :)

[andymatuschak]

Very nice sleuthing! Thank you for this.