Is this a case where stream sync would occur with an Isolate

[Silfalion]

Hello there,

Hope you're doing well.

So I've got a small issue where I'm trying to modify the DB from a background isolate, I can confirm the changes occur as when I switch widget(trigger a stream creation), the data is there and changed, but it doesn't happen synchronously. This is the code I'm using:

@pragma('vm:entry-point')
Future<void> isolateEntryPoint(int objectId, RootIsolateToken? token) async {
  void terminateIsolate() {
    debugPrint('Isolate terminated');

    IsolateNameServer.removePortNameMapping(objectId.toString());
    Isolate.current.kill();
  }

  final receivePort = ReceivePort();
  IsolateNameServer.registerPortWithName(
    receivePort.sendPort,
    objectId.toString(),
  );

  debugPrint('checking token');
  if (token == null) {
    terminateIsolate();
    return;
  }

  final databaseConnection = await DriftIsolate.inCurrent(
    () {
      BackgroundIsolateBinaryMessenger.ensureInitialized(token);

      return openConnection();
    },
    killIsolateWhenDone: true,
  ).connect();

  final localDataBaseRepository = LocalDatabaseRepositoryDriftImpl.createWithDb(
    driftLocalDatabase: DriftLocalDatabase(databaseConnection),
  );

  final objectManagerService =
      ObjectManagerServiceAndroid(database: localDataBaseRepository);

  await objectManagerService.changeobjectStatus(objectId: objectId, status: false);

  debugPrint('stats changed');

  receivePort.listen((message) {
    print('objectManagerService: $message');
  });

  terminateIsolate();
}

@pragma('vm:entry-point')
void printHello(int objectId) {
  final token = RootIsolateToken.instance;
  Isolate.spawn((message) => isolateEntryPoint(objectId, token), null);
}

printHello can be invoked while the app is in the background or when it's in the foreground.

I need the sync when the app is in the foreground for the UI, so for that I thought I could create an isolate to which the isolate above send a message like "give me the serialized connection" to use the same connection as the DB. It would create its own connection if no response is sent. Only thing is I'm wondering if there is an easier way to achieve this with drift existing API. Thank you in advance.

[Silfalion]

Managed to get it working initially, for one execution, with the following code that uses a separate isolate to sendPort(passing DriftIsolate fails with Isolate.spawn):

@pragma('vm:entry-point')
Future<void> isolateEntryPoint(int objectId, RootIsolateToken? token) async {
  var usesLocalConnection = false;
  late final DriftIsolate driftIsolate;

  DatabaseConnection? databaseConnection;

  late final LocalDatabaseRepository localDataBaseRepository;

  Future<void> terminateIsolate() async {
    IsolateNameServer.removePortNameMapping(objectId.toString());
    if (!usesLocalConnection) {
      await driftIsolate.shutdownAll();
    }

    debugPrint('Isolate terminated');
    Isolate.current.kill();
  }

  final receivePort = ReceivePort();
  IsolateNameServer.registerPortWithName(
    receivePort.sendPort,
    objectId.toString(),
  );

  final completer = Completer<SendPort>();

  debugPrint('checking token');
  if (token == null) {
    await terminateIsolate();
    return;
  }

  receivePort.listen((message) {
    if (message is SendPort) {
      debugPrint('received drift isolate');
      completer.complete(message);
      return;
    }
    debugPrint('objectManagerService: $message');
  });

  final sendPortLocalDrift =
      IsolateNameServer.lookupPortByName('localDriftDbIsolate');

  if (sendPortLocalDrift != null) {
    debugPrint('sending object id to locla drift isolate');
    sendPortLocalDrift.send('object:$objectId');

    await Future<void>.delayed(const Duration(milliseconds: 200));
  }
  if (completer.isCompleted) {
    debugPrint('connection isolate received from local drift isolate');
    usesLocalConnection = true;
    driftIsolate = DriftIsolate.fromConnectPort(await completer.future);
  } else {
    debugPrint(
      'no response from drift isolate, continuing with new connection',
    );

    driftIsolate = DriftIsolate.inCurrent(
      () {
        BackgroundIsolateBinaryMessenger.ensureInitialized(token);

        return openConnection();
      },
    );
  }

  databaseConnection = await driftIsolate.connect(isolateDebugLog: true);


  localDataBaseRepository = LocalDatabaseRepositoryDriftImpl.createWithDb(
    driftLocalDatabase: DriftLocalDatabase(databaseConnection),
  );

  final objectManagerService =
      objectManagerServiceAndroid(database: localDataBaseRepository);

  await objectManagerService.changeobjectStatus(objectId: objectId, status: false);

  debugPrint('stats changed');

  await terminateIsolate();
}

@pragma('vm:entry-point')
void printHello(int objectId) {
  final token = RootIsolateToken.instance;
  Isolate.spawn((message) => isolateEntryPoint(objectId, token), null);
}

However now, it hangs here on the second execution:

  databaseConnection = await driftIsolate.connect(isolateDebugLog: true);

any ideas?

Edit:

Corrected the line that's hanging

[simolus3]

If you're not already using a DriftIsolate, serializableConnection() returns a short-lived RPC server that can only be connected to once.

Are you using NativeDatabase.createInBackground() when connecting to the database in the UI? The problem should not happen that way, as we then create a long-lived database isolate either way.
The only other alternative I see is to have isolateEntryPoint always ask for the serialized connection and getting a new serializableConnection() every time. That should work if it connects to that once.

[Silfalion]

ohhh I see. Yes, I'm using NativeDatabase.createInBackground(). Hm, so the issue is serializableConnection. I'm reusing the same receive port for all requets. I guess I'll create a receiveport on the main isolate that will generate on a new connection on demand then.