Dart / Flutter: async behaviour of an Isolate's top level function

Question

Aye Aye good people, I'm experiencing a weird behavior

when using the top level function of an isolate asynchronously;

you can find example code HERE, but in short

as top level function of an isolate this works:

String _syncHandle(int data) {
  return 'done';
}

and this doesn't:

Future<String> _syncHandle(int data) async {
  return 'done';
}

can anybody explain me why?

(or if should work, why isn't doing so in my code?)

thank you in advance

Francesco

...

[edit: just noticed that a similar question has been asked,

nevertheless it is still unanswered Call async function from Isolate function,

plus issue open on github ]

Hi sir, I have same problem as you. Have you solved it yet? – hoangquyy Oct 01 '19 at 05:02 — hoangquyy, Oct 01 '19 at 05:02

score 0 · Accepted Answer · answered Oct 01 '19 at 21:40

forgot to update this :/ if you look at the code linked in the question

isolates_logging/lib/provider/test_isolate.dart

  Future<void> _handle(int _m) async {
    final response = ReceivePort();
    isolateTest = await Isolate.spawn(_isolate, response.sendPort);
    final sendPort = await response.first as SendPort;
    final answer = ReceivePort();
    sendPort.send([_m, answer.sendPort]);
    await answer.first.then((p) { 
      _outbound.sink.add(p);});
  }

  static void _isolate(SendPort _initialReplyTo) {
    final port =  ReceivePort();
    _initialReplyTo.send(port.sendPort);
    port.listen((message) {
      final data = message[0] as int;
      final send = message[1] as SendPort;
      send.send(_syncHandle(data));
    });
  }
}

Future<String> _syncHandle(int data) async {
  return 'done';
}

note the send.send(_syncHandle(data)); part

if you do so, you can send only primitives and not futures, basically that's it

Don't we need to create functions that we pass into the isolates as top level functions ?? Can we declare them inside, let's say a class ? I tried your code and It seems as everything is working even If I put it inside a class. What's the difference? — Divyam Dhadwal, Jan 26 '23 at 21:17

Dart / Flutter: async behaviour of an Isolate's top level function

1 Answers1

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