dart compute Illegal argument in isolate message

Question

I am using compute to do some work while keeping the UI running. The compute was working until I added another http call before it.

The working code is as follow

final ListRequest request =
        ListRequest(baseUrl: env['SERVER_URL']!, path: '/Items');

_mainController.updateListItems(
        await compute(_service.getItems, request));

I read some articles saying the function compute calls should be a top level function or a static function. However, the getItems is an instance function and there was no exception.

Recently I added a few lines and the code became

final Filter? filter = await _service.getFilter();

final ListRequest request =
        ListRequest(baseUrl: env['SERVER_URL']!, path: '/Items');

request.filter = filter;

_mainController.updateListItems(
        await compute(_service.getItems, request));

getFilter is a http call to retrieve some filter parameters from the backend.

Then I got the following error

Invalid argument(s): Illegal argument in isolate message: (object extends NativeWrapper - Library:'dart:io' Class: _SecureFilterImpl@13069316)

My dart and flutter versions are

Dart SDK version: 2.15.1 (stable)
Flutter 2.8.1

Thank you

=========================================================

Update

The Filter is

Filter {
  String? itemLocationSuburb;
  String? itemLocationPostcode;
}

Can you provide the definition for the `Filter` class? My guess is that `Filter` has a property of a type that is not supported by [SendPort.send](https://api.dart.dev/stable/2.17.3/dart-isolate/SendPort/send.html). — mmcdon20, Jun 18 '22 at 19:13
Hi @mmcdon20, thank you for your advice. I added the implementation of Filter. Both of them are nullable string so not sure what could be wrong. — Ben, Jun 19 '22 at 00:54
Nullable Strings should work fine, so I guess that isn't it. Is it possible to create a [minimal complete reproducible example](https://stackoverflow.com/help/minimal-reproducible-example)? — mmcdon20, Jun 19 '22 at 01:10
Thank you @mmcdon20, I will come back when the example is created. — Ben, Jun 20 '22 at 13:57

score 0 · Answer 1 · answered Jun 24 '22 at 12:49

Your _service service presumably contains a HttpClient. When you make a request through this client, it opens a connection to the HTTP server, and may maintain the connection after the request completes.

The HttpClient cannot be sent through a SendPort when it has open connections, but it is included in the scope of the getItems method.

To work around this issue, you can do one of the following:

Disable persistent connections with the HttpClientRequest.persistentConnection property
Make a new HttpClient to send through the compute function every time
Implement a long-lived background isolate to maintain its own HttpClient
Use the HttpClient in the main isolate, and only perform other work like parsing with compute (there's no significant benefit to using an isolate to make HTTP requests anyway)

dart compute Illegal argument in isolate message

1 Answers1