MultipleSyncAgents: Multiple sync agents attempted to join the same session #1708
Comments
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➤ PM Bot commented: Jira ticket: RDART-1049 |
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This exception gets thrown when you have multiple processes trying to open the same synchronized realm. This is not yet supported, though we do have work ongoing to enable it. My best guess here would be that you have a widget or a notification handler that's trying to open the Realm while the main app is also using it. |
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Thanks for the response. This is not the case in my app. I am just opening the realm once my app opens. Are you suggesting that I might call the Realm() constructor more than once? |
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Calling it in the same app/process multiple times is totally fine. If your app doesn't offer any multiprocess support, it's not obvious to me why you'd get that error. I'll need to check in with our android experts to see if they have an idea what could be going on. |
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@nirinchev I just remembered that there also was a similar ticket in realm-core (realm/realm-core#7190). Not sure if it helps |
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Hello @Navil
Does it crash on the second open? If so, please check the debug logs to see if there was a MultipleSyncAgents exception. |
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Hey @serhii-k. My app does not close when I press the "Back" button. However I tried the following things:
None of those led to the issue |
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Hello, |
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Thank you @Navil for trying. I see this error in a very simple usecase. I'm creating a flexible sync realm at the beginning of the main() function, and immediately closing this realm (so there shouldn't be any process connected to the realm). Then the app simply shows an empty scaffold. If I close this app with a "Back" button gesture, on the second run the app crashes with this error. I've tested on emulators with SDK 33 and 34. As well, as @tanguy-penfen has mentioned, this error is easily reproducible with the hot-reload feature. But in my case even with the internet connection. However, if I'm adding a realm.subscriptions.update(), followed by a call to waitForSynchronization(), this error doesn't occur on the second run. Here is a code for someone who can investigate this issue: import 'package:flutter/material.dart';
import 'package:realm/realm.dart';
import 'package:realm_test/model/model.dart';
Future<void> main() async {
WidgetsFlutterBinding.ensureInitialized();
// Create the app.
// Obtain the current user.
final config = Configuration.flexibleSync(
user,
[Point.schema],
);
final realm = Realm(config);
// If uncommented, there is no MultipleSyncAgents error.
// realm.subscriptions.update((mutableSubscriptions) {});
// await realm.subscriptions.waitForSynchronization();
realm.close();
runApp(const MaterialApp(home: Scaffold()));
} |
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@serhii-k Could I ask you to try building the app with this pattern: final app = App.getById(appId) ?? App(AppConfiguration(appId, ...));and report back. |
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@nielsenko |
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@tanguy-penfen print(Isolate.current.hashCode);
final app = App.getById(appId) ?? App(AppConfiguration(appId, ...));and report the values traced? |
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@nielsenko |
@nielsenko Awesome! This pattern actually worked great. I couldn't reproduce the error any more. As for the isolate hash, on my part it also changes for every run. Here are some values: |
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Thanks for confirming that the isolate changes. I would expect the same. BTW, be aware that the trick of calling We will need some time to replicate and discuss this. |
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It seems to be related not only to Android. I've started testing Realm on an iOS device, and by restarting a simple Flutter project, the same issue arises (I'm pressing Ctrl+R in Android Studio while the app is already running). It only happens with this setup: The simple code is mentioned in this comment. And the exception: |
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We have seen instances of this error too on hot restart (SHIFT + R) - will copy the stack trace when we see it again. We have to kill the app and 'flutter run' to start up from scratch to get past this error. |
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Also get this error on hot restart. final app = App.getById(appId) ?? App(AppConfiguration(appId));Seems to fix it. |
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This is however not a good solution as mentioned before. But it might be better than the app crashing. @nielsenko Do you know what kind of troubles we will run into using the workaround? |
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The problem is that the Client passed with Remember only the main isolate, not the process dies. Either when exiting and entering an app on Android, or hot-restarting the app on any platform (which is of course only happens for a developer, not a user). In particular there is a lot of cached stuff that still exists in core, which is why we end up here. My work-around might actually work if the old isolate can be kept alive under the hood, so that core can still call into it, but that will just be an ugly work-around, and I'm not sure it is even possible. The correct way to fix this is in core. I know they have been looking into it, but no fix exists yet. There is a lot of ongoing work regarding smarter multiprocess sync that is overlapping with this. |
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@Navil That said, I'm fairly certain you can lower the frequency of crashes with my work-around. This might bring you on the right side of the Android Store threshold, which I assume has value in itself. |
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I spend some time today, investigating when this regression was introduced. It turns out it was introduced with realm 2.1.0, which uses realm-core 14.5.2. The actual commit in realm-core is: realm/realm-core@255cb33 Now that we have pinpointed when the issue was introduced I suspect a fix will land soon, but if you feel the need you can downgrade to 2.0.0. Due to a breaking change in sane_uuid 1.0.0 that is not reflected in the version number, it is slightly complicated., but you can do it by adding the following dependency overrides to your dependency_overrides:
sane_uuid: 1.0.0-alpha.5
ejson: 0.3.0
realm: 2.0.0
realm_common: 2.0.0
realm_dart: 2.0.0
realm_generator: 2.0.0Also, don't use a newer version of Dart than 3.4.4 (ie. Flutter 3.22.3), as Dart 3.5 removed the deprecated UnmodifiableByteBufferView (see https://github.com/dart-lang/sdk/blob/main/CHANGELOG.md#darttyped_data) |
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Related to realm/realm-core#7190 |
Can you please illustrate with an example? I have the same problem. This could be the solution but I don't really understand how to do it. Thank you |
What happened?
I am seeing crashes for my users related to realm. I do not know how to reproduce it, but is is a crash that happens often enough to push my app above the Android Store threshold. This makes this topic relatively import for us.
Repro steps
Version
Flutter - Channel stable, 3.22.1
What Atlas Services are you using?
Both Atlas Device Sync and Atlas App Services
What type of application is this?
Flutter Application
Client OS and version
e.g. Redmi gale (Redmi 13C) Android 13 (SDK 33)
Code snippets
No response
Stacktrace of the exception/crash you're getting
Relevant log output
No response
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