[firebase_app_installations] Android ID-change callback throws on a background thread

[youngminz]

Is there an existing issue for this?

• I have searched the existing issues.

Which plugins are affected?

App Installations

Which platforms are affected?

Android

Description

On a fresh install, firebase_app_installations calls EventSink.success() from a Firebase background thread, causing a main-thread exception at TokenChannelStreamHandler.kt:25.

Reproduced in debug and release with the attached minimal project, which uses only Firebase Core and Installations.

Expected: ID-change events are delivered without a thread exception.

Environment: Samsung SM-S936N / Android 16; Dart 3.13.2; AGP 9.1.0 / Gradle 9.3.1.

Disclaimer: This issue report was written by GPT-6 Astra.

Reproducing the issue

1. Register a Firebase Android app for dev.example.installations_thread_mrp.
2. Create .local/firebase.json from config/firebase.example.json and fill in your Firebase configuration.
3. Uninstall any previous copy of the MRP, then run:

fvm flutter run --debug --dart-define-from-file=.local/firebase.json

The app subscribes to onIdChange and calls getId() followed by getToken() immediately after Firebase initialization. Leave it untouched and inspect adb logcat: getId() completes, then the native exception occurs.

Core sequence from the MRP (UI and logging omitted; firebaseOptions contains your Firebase app configuration):

await Firebase.initializeApp(options: firebaseOptions);

final installations = FirebaseInstallations.instance;
_subscription = installations.onIdChange.listen((_) {});

// No delay after initialization.
await installations.getId();
await installations.getToken();

flutterfire-installations-mrp.zip

Firebase Core version

4.14.0

Flutter Version

3.47.2

Relevant Log Output

java.lang.RuntimeException: Methods marked with @UiThread must be executed on the main thread. Current thread: Firebase Blocking Thread #0
	at io.flutter.embedding.engine.FlutterJNI.ensureRunningOnMainThread(FlutterJNI.java:1695)
	at io.flutter.embedding.engine.FlutterJNI.dispatchPlatformMessage(FlutterJNI.java:1177)
	at io.flutter.embedding.engine.dart.DartMessenger.send(DartMessenger.java:275)
	at io.flutter.embedding.engine.dart.DartExecutor$DefaultBinaryMessenger.send(DartExecutor.java:457)
	at io.flutter.embedding.engine.dart.DartExecutor.send(DartExecutor.java:217)
	at io.flutter.plugin.common.EventChannel$IncomingStreamRequestHandler$EventSinkImplementation.success(EventChannel.java:251)
	at io.flutter.plugins.firebase.installations.firebase_app_installations.TokenChannelStreamHandler.createTokenEventListener$lambda$0(TokenChannelStreamHandler.kt:25)
	at io.flutter.plugins.firebase.installations.firebase_app_installations.TokenChannelStreamHandler$$ExternalSyntheticLambda0.onFidChanged(D8$$SyntheticClass:0)
	at com.google.firebase.installations.FirebaseInstallations.checkAndUpdateFidListeners(FirebaseInstallations.java:454)
	at com.google.firebase.installations.FirebaseInstallations.doNetworkCallIfNecessary(FirebaseInstallations.java:413)
	at com.google.firebase.installations.FirebaseInstallations.lambda$doRegistrationOrRefresh$3$com-google-firebase-installations-FirebaseInstallations(FirebaseInstallations.java:382)
	at com.google.firebase.installations.FirebaseInstallations$$ExternalSyntheticLambda1.run(D8$$SyntheticClass:0)
	at com.google.firebase.concurrent.SequentialExecutor$1.run(SequentialExecutor.java:117)
	at com.google.firebase.concurrent.SequentialExecutor$QueueWorker.workOnQueue(SequentialExecutor.java:229)
	at com.google.firebase.concurrent.SequentialExecutor$QueueWorker.run(SequentialExecutor.java:174)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1100)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at com.google.firebase.concurrent.CustomThreadFactory.lambda$newThread$0$com-google-firebase-concurrent-CustomThreadFactory(CustomThreadFactory.java:47)
	at com.google.firebase.concurrent.CustomThreadFactory$$ExternalSyntheticLambda0.run(D8$$SyntheticClass:0)
	at java.lang.Thread.run(Thread.java:1572)

Flutter dependencies

Dependency versions

firebase_core: 4.14.0
firebase_app_installations: 0.4.3
firebase_core_platform_interface: 8.1.1
firebase_app_installations_platform_interface: 0.1.5
_flutterfire_internals: 1.3.77

The complete pubspec.lock is included in the project ZIP.

Additional context and comments

Suggested fix

Dispatch the event on the main looper:

return FidListener { token ->
  Handler(Looper.getMainLooper()).post {
    events.success(mapOf("token" to token))
  }
}

This change resolved the exception in the original application's release build.

[SelaseKay]

Hi @youngminz, thanks for the report. I'm looking into it.

[SelaseKay]

Hi @youngminz, thanks for the report and the MRP — that sequence made this straightforward to confirm.

This is a bug in the Android plugin. FidListener is invoked on Firebase’s blocking executor, and we were calling EventSink.success() on that same thread. Flutter requires platform messages on the main thread, which is what produced the @UiThread exception.

Your suggested main-looper hop is the right fix. That’s now in #18652 — events are posted onto Looper.getMainLooper(), and we also unregister the FidListenerHandle on cancel.