Ports shared through IsolateNameServer have unexpected behavior

[iazel]

Steps to reproduce

1. Register a port through IsolateNameServer.registerPortWithName
2. Either don't listen on the port, or close the port, or Isolate.kill() the given isolate
3. Retrieve the port through IsolateNameServer.lookupPortByName
4. Send a custom class through send

Please be aware that it is important to send a custom class, otherwise the issue does not exist.

Another interesting aspect is that if we get port before it is closed, and keep using it, then no issue arise.

Expected results

Ports normally exhibit the following behavior:

• Messages sent to a port that isn't ready (i.e. not listening), will be delivered as soon as listen is called
• Sending messages to a closed port is a no-op
• Data can be sent according to documentation, including the same-code ones

Actual results

When using data types supported across different code-bases (e.g: int, string, etc...), no issues arise.

When using data types supported only on same code-bases (e.g. custom classes), then ArgumentError is thrown on port.send if the receiving end is somehow closed or not ready.

Code sample

Code sample

import 'dart:isolate';
import 'dart:ui';

import 'package:flutter_test/flutter_test.dart';

final class A {
}

void main() {
  test('isolate', () async {
    TestWidgetsFlutterBinding.ensureInitialized();
    await Isolate.spawn(
      (_) {
        final port = ReceivePort();
        port.listen((_) {
          Isolate.exit();
        });
        IsolateNameServer.registerPortWithName(port.sendPort, 'test');
      },
      null,
    );

    while (IsolateNameServer.lookupPortByName('test') == null) {
      await Future<void>.delayed(const Duration(milliseconds: 100));
    }

    for (var i = 0; i < 10; ++i) {
      IsolateNameServer.lookupPortByName('test')?.send(A());
      await Future<void>.delayed(const Duration(milliseconds: 100));
    }
  });
}

Screenshots or Video

No response

Logs

Logs

dart:isolate                  _SendPort.send
test/isolate_test.dart 28:51  main.<fn>

Invalid argument: is a regular instance reachable via : Instance of 'A'

Flutter Doctor output

Doctor output

Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel stable, 3.19.6, on Ubuntu 23.10 6.5.0-28-generic, locale en_US.UTF-8)
[✓] Android toolchain - develop for Android devices (Android SDK version 34.0.0)
[✓] Chrome - develop for the web
[✓] Linux toolchain - develop for Linux desktop
[✓] Android Studio (version 2023.2)
[✓] IntelliJ IDEA Community Edition (version 2023.3)
[✓] Connected device (2 available)
[✓] Network resources

• No issues found!

[iazel]

After further analysis on Android, in case the main Activity is destroyed (i.e. AppLifecycleState.detached), even though the Isolate still runs in background, once we open back the app, port will be limited on sending data as if they didn't share the same codebase.

Notice that even if we get paused, the app will work without problems. It is only the detached state that causes problems.

This can be easily tested on Android by enabling Don't keep activities in Developer options settings.

Code sample:

import 'dart:async';
import 'dart:isolate';
import 'dart:ui';

import 'package:flutter/material.dart';

void main() {
    runApp(MyApp());
}

final class A {}

final class MyApp extends StatefulWidget {
  const MyApp({super.key});

  @override
  State<StatefulWidget> createState() {
    return _MyAppState();
  }
}

final class _MyAppState extends State<MyApp> {
  @override
  void initState() {
    super.initState();
    final port = IsolateNameServer.lookupPortByName('name');
    if (port == null) {
      Isolate.spawn((_) async {
        final port = ReceivePort();
        port.listen((message) {
          print('got $message');
        });
        IsolateNameServer.registerPortWithName(port.sendPort, 'name');
        var i = 0;
        while (true) {
          ++i;
          await Future<void>.delayed(const Duration(seconds: 5));
          print('looped $i times');
        }
      }, null);
    } else {
      port.send(A());
    }
  }

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      home: Scaffold(
        body: Text('Hello World'),
      ),
    );
  }
}

By changing send to something like:

port.send('restarted');

It will work as expected.

[huycozy]

Thanks for the report. I also see the issue with the test and Don't keep activities on app as reported. This doesn't seem to belong to Android as I see the same test failed on macOS. Labeling the issue for engine team input.

flutter doctor -v (stable and master)

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[!] Flutter (Channel master, 3.22.0-18.0.pre.53, on macOS 14.1 23B74 darwin-x64, locale en-VN)
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[✓] Android toolchain - develop for Android devices (Android SDK version 34.0.0)
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    • Platform android-34, build-tools 34.0.0
    • ANDROID_HOME = /Users/huynq/Library/Android/sdk
    • Java binary at: /Applications/Android Studio.app/Contents/jbr/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 17.0.9+0-17.0.9b1087.7-11185874)
    • All Android licenses accepted.

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    • Build 15E204a
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[✓] Chrome - develop for the web
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! Doctor found issues in 1 category.

[a-siva]

//cc @aam

[aam]

The issue with original code #147469 (comment) is that registered isolate exits once it receives first message, so no further sends will work. It's confusing of course that the error talks about invalid object and only shows up if it's an instance of user-defined class being sent, it silently does nothing if primitive object is being sent.

[iazel]

The issue with original code #147469 (comment) is that registered isolate exits once it receives first message, so no further sends will work. It's confusing of course that the error talks about invalid object and only shows up if it's an instance of user-defined class being sent, it silently does nothing if primitive object is being sent.

Yes, we exit the isolate just to showcase the diverging behaviour. Is it expected for send to fail in case the port is closed/not available?

[aam]

Is it expected for send to fail in case the port is closed/not available?

No, it's not. Send should not behave differently whether port is open or closed. The underlying root cause of the exception is gap in the dart vm api Dart_NewSendPort/Dart_SendPortGetId that IsolateNameServer uses to keep track of opened send ports.

[aam]

The fix should have been rolled in flutter at 21da3a8, main channel at this point

[iazel]

@aam do you know if the fix will also solve #113825 and #119589 ?

[aam]

@aam do you know if the fix will also solve #113825 and #119589 ?

I don't think those issues are related to this.