Disconnect while connecting (fetching credentials)

[js2702]

In our app we would like to do some checks during the fetch credentials callback and depending on the result abort the retry mechanism.

If we disconnect we get a recursive lock error, so we looked into the code and saw there is an internal function: _abortCurrentSync. We tried exposing it and it works as expected.

Is there any other way to do what we are trying to do or exposing this internal function would be the only way? If so we can open a PR.

[simolus3]

We can't expose _abortCurrentSync as-is without possibly introducing concurrrency issues. I we can make calling disconnect() work though (as long as you don't await it, that's an immediate deadlock). I'll take a look!

[davidmartos96]

@simolus3 Thank you! We are trying the new commit, but we are still finding the LockError when calling disconnect in the fetchCredentials callback.

What would be the code from the user perspective?

Future<PowerSyncCredentials?> fetchCredentials() async {
    // some checks
   
    psDb.disconnect();
    throw Exception("Forced disconnection");
}

We've also tried disconnect with a Future.microtask, returning null, and a combination. But all are throwing the LockError.

LockError: Recursive lock is not allowed
[Flutter] │ #0   SimpleMutex.lock (package:sqlite_async/src/native/native_isolate_mutex.dart:37:7)
[Flutter] │ #1   PowerSyncDatabaseMixin.disconnect (package:powersync_core/src/database/powersync_db_mixin.dart:348:41)

[simolus3]

Thanks for the follow-up. I agree that the code is correct from a user perspective, and I'm quite confused that this apparently works in a test.

A quick workaround might be to do Zone.root.run(psDb.disconnect) (not a huge fan of that though).

[davidmartos96]

@simolus3 Using Zone.root.run(psDb.disconnect) works. Thank you!

Could it be because our Flutter app uses the following configuration in main?

await runZonedGuarded(() async {
    WidgetsFlutterBinding.ensureInitialized();
    runApp(...);
  }, (exception, stackTrace) async {
    await Sentry.captureException(exception, stackTrace: stackTrace);
  });

[simolus3]

Good catch, but it really shouldn't. The fix involved remembering the Zone that called connect itself and then binding async callbacks (like fetchCredentials) to that zone. So since the outer zone doesn't have the mutex in its zone variables (otherwise it couldn't connect), fetchCredentials should be able to call disconnect().

[davidmartos96]

@simolus3 After another try, it seems like the commit works by default. Not really sure what was happening. Sorry for the confusion!
Thank you!