samples/isolate_example/lib/page_three.dart

// Copyright 2019-present the Flutter authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'dart:isolate';
import 'dart:math';

class DataTransferPageStarter extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ChangeNotifierProvider(
      builder: (context) => DataTransferIsolateController(),
      child: DataTransferPage(),
    );
  }
}

class DataTransferPage extends StatelessWidget {
  @override
  Widget build(context) {
    return SafeArea(
      child: Column(
        mainAxisSize: MainAxisSize.min,
        children: [
          Container(
            child: Text(
              'Number Generator Progress',
              style: Theme.of(context).textTheme.title,
            ),
            padding: EdgeInsets.all(8),
          ),
          LinearProgressIndicator(
            value: Provider.of<DataTransferIsolateController>(context)
                .progressPercent,
            backgroundColor: Colors.grey[200],
          ),
          Expanded(child: RunningList()),
          Column(
            mainAxisSize: MainAxisSize.min,
            children: [
              Row(
                mainAxisAlignment: MainAxisAlignment.center,
                children: [createButtons(context)],
              ),
            ],
          ),
        ],
      ),
    );
  }
}

class DataTransferIsolateController extends ChangeNotifier {
  Isolate _newIsolate;
  ReceivePort _mIceRP;
  SendPort _newIceSP;

  final currentProgress = <String>[];
  bool running = false;
  Stopwatch _timer = Stopwatch();
  double progressPercent = 0;

  DataTransferIsolateController() {
    createIsolate();
    listen();
  }

  Future<void> createIsolate() async {
    _mIceRP = ReceivePort();
    _newIsolate =
        await Isolate.spawn(_secondIsolateEntryPoint, _mIceRP.sendPort);
  }

  void listen() {
    _mIceRP.listen((dynamic message) {
      if (message is SendPort) _newIceSP = message;

      if (message is int) {
        currentProgress.insert(
            0, '$message% - ${_timer.elapsedMilliseconds / 1000} Sec');
        progressPercent = message / 100;
      }

      if (message is String && message == 'done') {
        running = false;
        _timer.stop();
      }

      notifyListeners();
    });
  }

  void generateOnSecondaryIsolate() {
    if (running) return;

    running = true;
    _timer.reset();
    currentProgress.clear();

    _timer.start();
    _newIceSP.send('start');

    notifyListeners();
  }

  Future<void> generateRandomNumbers() async {
    if (running) return;

    running = true;
    Random rng = Random();
    _timer = Stopwatch();

    currentProgress.clear();
    _timer.start();

    List<int> randNums = [];
    for (int i = 0; i < 100; i++) {
      randNums.clear();

      for (int j = 0; j < 1000000; j++) {
        randNums.add(rng.nextInt(100));
      }
      await sendNumbers(randNums);
    }
  }

  Future<void> sendNumbers(List<int> numList) async {
    return Future<void>(() {
      _newIceSP.send(numList);
    });
  }

  Isolate get newIsolate => _newIsolate;

  void dispose() {
    super.dispose();
    _newIsolate?.kill(priority: Isolate.immediate);
    _newIsolate = null;
  }
}

class RunningList extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final controller = Provider.of<DataTransferIsolateController>(context);
    final progress = controller.currentProgress;

    return DecoratedBox(
      decoration: BoxDecoration(
        color: Colors.grey[200],
      ),
      child: ListView.builder(
        itemCount: progress.length,
        itemBuilder: (context, index) {
          return Column(
            children: [
              Card(
                child: ListTile(
                  title: Text(progress[index]),
                ),
                color: Colors.lightGreenAccent,
              ),
              Divider(
                color: Colors.blue,
                height: 3,
              ),
            ],
          );
        },
      ),
    );
  }
}

Future<void> _secondIsolateEntryPoint(SendPort callerSP) async {
  ReceivePort newIceRP = ReceivePort();
  callerSP.send(newIceRP.sendPort);

  newIceRP.listen(
    (dynamic message) async {
      if (message is String && message == 'start') {
        await generateAndSum(callerSP, createNums());

        callerSP.send('done');
      } else {
        await generateAndSum(callerSP, message as List<int>);

        callerSP.send('done');
      }
    },
  );
}

Iterable<int> createNums() sync* {
  final rng = Random();
  for (int i = 0; i < 100000000; i++) {
    yield rng.nextInt(100);
  }
}

Future<void> generateAndSum(SendPort callerSP, Iterable<int> iter) async {
  int sum = 0;
  int count = 0;

  for (int x in iter) {
    sum += x;
    count++;
    if ((count + 1) % 1000000 == 0) {
      callerSP.send((count + 1) ~/ 1000000);
    }
  }

  return sum;
}

Widget createButtons(BuildContext context) {
  final controller =
      Provider.of<DataTransferIsolateController>(context, listen: false);
  return ButtonBar(
    alignment: MainAxisAlignment.center,
    children: [
      Column(
        children: [
          RaisedButton(
            child: const Text('Transfer Data to 2nd Isolate'),
            elevation: 8.0,
            onPressed: controller.generateRandomNumbers,
          ),
          RaisedButton(
            child: const Text('Generate on 2nd Isolate'),
            elevation: 8.0,
            onPressed: controller.generateOnSecondaryIsolate,
          ),
        ],
      ),
    ],
  );
}