http requests throw when called from Isolate.run() but work when called from compute()

[Wizzel1]

• Dart v2.19.6
• MacOS

I am trying to execute a http request from an Isolate.

Future<String> myRequest(String argument) async {
  final response = await http.get(
   ///request Code
  );
  return response.body;
}

when I try to run it with Isolate.run() like this

 final test = await Isolate.run(
        () => myRequest(argument),
      );

I am getting an error :
ArgumentError (Invalid argument(s): Illegal argument in isolate message: (object extends NativeWrapper - Library:'dart:ui' Class: Paragraph))
but when I run it with compute

 final test = await compute(myRequest, argument);

it works. Is this intended?

[julemand101]

Are you running your code in a browser?
Also, it seems you forgot to paste the error message into your issue. Can you please add it?

[Wizzel1]

@julemand101
No, it is running on a mac. Sorry, I have edited the error message.

[lrhn]

Definitely not running in a browser, since dart:isolate is not available on the web.

My best guess is that the closure () => myRequest(argument) closes over more state than necessary, and some of that state cannot be sent. (And the error message supports that.)

Try adding a top-level helper like:

R Function() curryFunction<R, T>(R Function(T) function, T argument) => () => function(argument);

and do:

final test = await Isolate.run(curryFunction(myRequest, argument));`

That should ensure that the ()=>myRequest(argument) closure is created in a scope with no extra variables to over-capture.

Q.v. #36983

[Wizzel1]

Yes, now it works. However, I don't quite understand the problem. Is this a mistake I made or a bug in dart?

[lrhn]

I think it's a bug, which is why #36983 (and the duplicate #50462 that I filed) exist.

It's a gnarly problem for the VM implementation, because it goes to the heart of their closure implementation, but I hope it will be fixed eventually. (Preferably soon, because this is just the most visible way to see the problem, but overcapturing can also have a memory cost if large values are kept alive, even if nobody needs them.)

[Wizzel1]

I see. Thanks for your quick help!