Posted on Apr 4, 2021

About Dart's Isolate (1)

#dart #isolate #dartlang

I want to explain about How to distribute the load with Isolate.
And In this Document, I'll confirm about isolate basic usage before explain it.

Hello Isolate

We can write multi-threads like programming code to use Isolate.

import 'dart:isolate' as iso;

onMain(message) async {
  //
  print("child:arg:${message}");
  for (var i = 0; i < 5; i++) {
    await Future.delayed(Duration(milliseconds: 100));
    print("child:print:${i}");
  }
}

main() async {
  iso.Isolate.spawn(onMain, "Hi");
  for (var i = 0; i < 5; i++) {
    await Future.delayed(Duration(milliseconds: 100));
    print("parent:print:${i}");
  }
}

$ dart bin/main_example_isolate_01.dart 
child:arg:Hi
parent:print:0
child:print:0
parent:print:1
child:print:1
parent:print:2
child:print:2
parent:print:3
child:print:3
parent:print:4

code https://github.com/kyorohiro/hao_dart_server_and_systemd/blob/master/bin/main_example_isolate_01.dart

Communication For Each Isolate

Parent Isolate and Child Isolate can not share memory.
if you want to share data both isolate, you must to use SendPort and ReceivePort.

import 'dart:isolate' as iso;

onMain(message) async {
  //
  print("child:arg:${message}");
  iso.SendPort sendPort = message['p'];
  for (var i = 0; i < 5; i++) {
    await Future.delayed(Duration(milliseconds: 100));
    print("child:print:${i}");
    sendPort.send("hi${i}");
  }
}

main() async {
  iso.ReceivePort receivePort = iso.ReceivePort();
  receivePort.listen((message) {
    print("parent:onMessage: ${message}");
  });
  iso.Isolate.spawn(onMain, {"v": "Hi", "p": receivePort.sendPort});
  for (var i = 0; i < 5; i++) {
    await Future.delayed(Duration(milliseconds: 100));
    print("parent:print:${i}");
  }
  receivePort.close();
}

$ dart bin/main_example_isolate_02.dart 
child:arg:{v: Hi, p: SendPort}
parent:print:0
child:print:0
parent:onMessage: hi0
parent:print:1
child:print:1
parent:onMessage: hi1
parent:print:2
child:print:2
parent:onMessage: hi2
parent:print:3
child:print:3
parent:onMessage: hi3
parent:print:4
child:print:4
parent:onMessage: hi4