Creating a separate thread for a question stated in a comment...
How does ObjectBox handle concurrent(by different threads/isolates) write requests? example of my use case: FCM "onBackgroundmessage" call runs in a different isolate, the same time multiple write requests might happen. "Hive" is failing in this case completely. Is there any inbuild solution in ObjectBox?
ObjectBox for dart is based on a native ObjectBox core library that handles concurrency using Transactions. Let me pick out few points relevant to the question:
As for the isolates in Dart/Flutter - yes, they can safely access the same store, you just need to make sure it really is the same native store instance. To do so, you do the following steps:
Store() instance in your main isolate, as you normally would.ByteData store.reference which contains the information about the native store.SendPort.Store instance, using Store.fromReference(getObjectBoxModel(), msg as ByteData).Store instances which internally use the same underlying native store. Therefore, their transactions are synchronized, they both see the same data and get notifications on data changes. 🎉You can see the code I've just described this test case: https://github.com/objectbox/objectbox-dart/blob/461a948439dcc42f3956b7d21b232eb9c2bc26e1/objectbox/test/isolates_test.dart#L50
Make sure you don't close the store while another isolate is still using it. Better not close it at all - that's best practice in normal applications without huge amounts of background work.
A few years later from the accepted answer, objectbox now has an additional function that can work well with an isolate.
This is the Store.attach() function. Using this function, you can attach a store by providing the database path without having to worry about a separate isolate closing the store:
The actual underlying store is only closed when the last store instance is closed (e.g. when the app exits).
In my own case, I had to use the workmanager package to execute a background task that depends on the objectbox store.
You can create an "initializer" class like so:
class ObjectBox {
static late final Store store;
static Future initialize() async {
var docsDir = await getApplicationDocumentsDirectory();
var dbPath = p.join(docsDir.path, "objectbox");
if (Store.isOpen(dbPath)) {
store = Store.attach(getObjectBoxModel(), dbPath);
} else {
store = await openStore(directory: dbPath);
}
}
}
Once you have this, you can then use the initialize() in your isolate. Example with the workmanager package:
main.dart
@pragma("vm:entry-point")
void callbackDispatcher() {
Workmanager().executeTask((taskName, inputData) async {
await ObjectBox.initialize(); // Initialize in background isolate.
return true;
});
}
Future<void> main() async {
WidgetsFlutterBinding.ensureInitialized();
await ObjectBox.initialize(); // Initialize in main isolate
Workmanager().initialize(callbackDispatcher);
runApp(const MyApp());
}
This way, even if you close the database in your main isolate, the background isolate will still continue to function. The underlying store itself is closed once all store instances are closed.
Feel free to check isolated_box library. This box is build on top on Hive with the same API but different init and is multi-isolate.
