JArray.getRange() has thread-safety problem

[brandon3343]

Future<Uint8List> getIcon(String packageName) async {
    final JArray<jbyte> jArray = await getIconFromAndroid(packageName);

    // There is a thread safety issue with the following line of code, 
    return jArray.getRange(0, jArray.length).buffer.asUint8List();
}

multiple executions test(), the return value maybe incorrect.

Isolate.run(() async {
    final icon = getIcon('package1'); // maybe incorret
});
Isolate.run(() async  {
    final icon = getIcon('package2'); // maybe incorret
});

[HosseinYousefi]

What is getIconFromAndroid? Also you're not awaiting the result of getIcon in Isolate.run.

Please post a minimal reproducible failing code without external dependencies.

[brandon3343]

Sorry, this is the smallest example.

the code is in app_icon.dart -> _AppIconState -> _getIcon()

class _AppIconState extends State<AppIcon> {
···
  @override
  void initState() {
    super.initState();
    _getIcon();  
    // _getIconFixed();
  }
···
}

file

jnigen_example.zip

screenshot when called _getIcon()

screenshot when called _getIconFixed()

[HosseinYousefi]

This seems to be a problem with the native finalizer @dcharkes.

When I try using a custom allocator (that is not recognized by package:jni to have a nativeFree), it works:

class CustomAlloc implements Allocator {
  @override
  Pointer<T> allocate<T extends NativeType>(int byteCount, {int? alignment}) {
    return malloc.allocate(byteCount, alignment: alignment);
  }

  @override
  void free(Pointer<NativeType> pointer) {
    return malloc.free(pointer);
  }
}

And later on:

final list = iconByteArray
    .getRange(0, iconByteArray.length, allocator: CustomAlloc())
    .buffer
    .asUint8List();

In general you would want to manage the memory yourself, since keeping all of the lists inside the _cache Map would keep them forever. So your implementation of CustomAlloc could also manage the images, for instance, based on the view portion of the list view.

[HosseinYousefi]

As mentioned, this is happening due to dart-lang/sdk#55800. Moving this to backlog.