examples/layers/services/isolate.dart - mirrors/flutter - Git at Google

 // Copyright 2014 The Flutter Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 import 'dart:convert';
 import 'dart:isolate';

 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';

 typedef OnProgressListener = void Function(double completed, double total);
 typedef OnResultListener = void Function(String result);

 // An encapsulation of a large amount of synchronous processing.
 //
 // The choice of JSON parsing here is meant as an example that might surface
 // in real-world applications.
 class Calculator {
   Calculator({ required this.onProgressListener, required this.onResultListener, String? data })
     : assert(onProgressListener != null),
       assert(onResultListener != null),
       // In order to keep the example files smaller, we "cheat" a little and
       // replicate our small json string into a 10,000-element array.
       _data = _replicateJson(data, 10000);

   final OnProgressListener onProgressListener;
   final OnResultListener onResultListener;
   final String _data;
   // This example assumes that the number of objects to parse is known in
   // advance. In a real-world situation, this might not be true; in that case,
   // the app might choose to display an indeterminate progress indicator.
   static const int _NUM_ITEMS = 110000;
   static const int _NOTIFY_INTERVAL = 1000;

   // Run the computation associated with this Calculator.
   void run() {
     int i = 0;
     final JsonDecoder decoder = JsonDecoder(
       (dynamic key, dynamic value) {
         if (key is int && i++ % _NOTIFY_INTERVAL == 0)
           onProgressListener(i.toDouble(), _NUM_ITEMS.toDouble());
         return value;
       },
     );
     try {
       final List<dynamic> result = decoder.convert(_data) as List<dynamic>;
       final int n = result.length;
       onResultListener('Decoded $n results');
     } on FormatException catch (e, stack) {
       debugPrint('Invalid JSON file: $e');
       debugPrint('$stack');
     }
   }

   static String _replicateJson(String? data, int count) {
     final StringBuffer buffer = StringBuffer()..write('[');
     for (int i = 0; i < count; i++) {
       buffer.write(data);
       if (i < count - 1)
         buffer.write(',');
     }
     buffer.write(']');
     return buffer.toString();
   }
 }

 // The current state of the calculation.
 enum CalculationState {
   idle,
   loading,
   calculating
 }

 // Structured message to initialize the spawned isolate.
 class CalculationMessage {
   CalculationMessage(this.data, this.sendPort);
   String data;
   SendPort sendPort;
 }

 // A manager for the connection to a spawned isolate.
 //
 // Isolates communicate with each other via ReceivePorts and SendPorts.
 // This class manages these ports and maintains state related to the
 // progress of the background computation.
 class CalculationManager {
   CalculationManager({ required this.onProgressListener, required this.onResultListener })
     : assert(onProgressListener != null),
       assert(onResultListener != null),
       _receivePort = ReceivePort() {
     _receivePort.listen(_handleMessage);
   }

   CalculationState _state = CalculationState.idle;
   CalculationState get state => _state;
   bool get isRunning => _state != CalculationState.idle;

   double _completed = 0.0;
   double _total = 1.0;

   final OnProgressListener onProgressListener;
   final OnResultListener onResultListener;

   // Start the background computation.
   //
   // Does nothing if the computation is already running.
   void start() {
     if (!isRunning) {
       _state = CalculationState.loading;
       _runCalculation();
     }
   }

   // Stop the background computation.
   //
   // Kills the isolate immediately, if spawned. Does nothing if the
   // computation is not running.
   void stop() {
     if (isRunning) {
       _state = CalculationState.idle;
       if (_isolate != null) {
         _isolate!.kill(priority: Isolate.immediate);
         _isolate = null;
         _completed = 0.0;
         _total = 1.0;
       }
     }
   }

   final ReceivePort _receivePort;
   Isolate? _isolate;

   void _runCalculation() {
     // Load the JSON string. This is done in the main isolate because spawned
     // isolates do not have access to the root bundle. However, the loading
     // process is asynchronous, so the UI will not block while the file is
     // loaded.
     rootBundle.loadString('services/data.json').then<void>((String data) {
       if (isRunning) {
         final CalculationMessage message = CalculationMessage(data, _receivePort.sendPort);
         // Spawn an isolate to JSON-parse the file contents. The JSON parsing
         // is synchronous, so if done in the main isolate, the UI would block.
         Isolate.spawn<CalculationMessage>(_calculate, message).then<void>((Isolate isolate) {
           if (!isRunning) {
             isolate.kill(priority: Isolate.immediate);
           } else {
             _state = CalculationState.calculating;
             _isolate = isolate;
           }
         });
       }
     });
   }

   void _handleMessage(dynamic message) {
     if (message is List<double>) {
       _completed = message[0];
       _total = message[1];
       onProgressListener(_completed, _total);
     } else if (message is String) {
       _completed = 0.0;
       _total = 1.0;
       _isolate = null;
       _state = CalculationState.idle;
       onResultListener(message);
     }
   }

   // Main entry point for the spawned isolate.
   //
   // This entry point must be static, and its (single) argument must match
   // the message passed in Isolate.spawn above. Typically, some part of the
   // message will contain a SendPort so that the spawned isolate can
   // communicate back to the main isolate.
   //
   // Static and global variables are initialized anew in the spawned isolate,
   // in a separate memory space.
   static void _calculate(CalculationMessage message) {
     final SendPort sender = message.sendPort;
     final Calculator calculator = Calculator(
       onProgressListener: (double completed, double total) {
         sender.send(<double>[ completed, total ]);
       },
       onResultListener: sender.send,
       data: message.data,
     );
     calculator.run();
   }
 }

 // Main app widget.
 //
 // The app shows a simple UI that allows control of the background computation,
 // as well as an animation to illustrate that the UI does not block while this
 // computation is performed.
 //
 // This is a StatefulWidget in order to hold the CalculationManager and
 // the AnimationController for the running animation.
 class IsolateExampleWidget extends StatefulWidget {
   const IsolateExampleWidget({super.key});

   @override
   IsolateExampleState createState() => IsolateExampleState();
 }

 // Main application state.
 class IsolateExampleState extends State<StatefulWidget> with SingleTickerProviderStateMixin {

   String _status = 'Idle';
   String _label = 'Start';
   String _result = ' ';
   double _progress = 0.0;
   late final AnimationController _animation = AnimationController(
     duration: const Duration(milliseconds: 3600),
     vsync: this,
   )..repeat();
   late final CalculationManager _calculationManager = CalculationManager(
     onProgressListener: _handleProgressUpdate,
     onResultListener: _handleResult,
   );

   @override
   void dispose() {
     _animation.dispose();
     super.dispose();
   }

   @override
   Widget build(BuildContext context) {
     return Material(
       child: Column(
         mainAxisAlignment: MainAxisAlignment.spaceAround,
         children: <Widget>[
           RotationTransition(
             turns: _animation,
             child: Container(
               width: 120.0,
               height: 120.0,
               color: const Color(0xFF882222),
             ),
           ),
           Opacity(
             opacity: _calculationManager.isRunning ? 1.0 : 0.0,
             child: CircularProgressIndicator(
               value: _progress,
             ),
           ),
           Text(_status),
           Center(
             child: ElevatedButton(
               onPressed: _handleButtonPressed,
               child: Text(_label),
             ),
           ),
           Text(_result),
         ],
       ),
     );
   }

   void _handleProgressUpdate(double completed, double total) {
     _updateState(' ', completed / total);
   }

   void _handleResult(String result) {
     _updateState(result, 0.0);
   }

   void _handleButtonPressed() {
     if (_calculationManager.isRunning)
       _calculationManager.stop();
     else
       _calculationManager.start();
     _updateState(' ', 0.0);
   }

   String _getStatus(CalculationState state) {
     switch (state) {
       case CalculationState.loading:
         return 'Loading...';
       case CalculationState.calculating:
         return 'In Progress';
       case CalculationState.idle:
         return 'Idle';
     }
   }

   void _updateState(String result, double progress) {
     setState(() {
       _result = result;
       _progress = progress;
       _label = _calculationManager.isRunning ? 'Stop' : 'Start';
       _status = _getStatus(_calculationManager.state);
     });
   }
 }

 void main() {
   runApp(const MaterialApp(home: IsolateExampleWidget()));
 }
	// Copyright 2014 The Flutter Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	import 'dart:convert';
	import 'dart:isolate';

	import 'package:flutter/material.dart';
	import 'package:flutter/services.dart';

	typedef OnProgressListener = void Function(double completed, double total);
	typedef OnResultListener = void Function(String result);

	// An encapsulation of a large amount of synchronous processing.
	//
	// The choice of JSON parsing here is meant as an example that might surface
	// in real-world applications.
	class Calculator {
	Calculator({ required this.onProgressListener, required this.onResultListener, String? data })
	: assert(onProgressListener != null),
	assert(onResultListener != null),
	// In order to keep the example files smaller, we "cheat" a little and
	// replicate our small json string into a 10,000-element array.
	_data = _replicateJson(data, 10000);

	final OnProgressListener onProgressListener;
	final OnResultListener onResultListener;
	final String _data;
	// This example assumes that the number of objects to parse is known in
	// advance. In a real-world situation, this might not be true; in that case,
	// the app might choose to display an indeterminate progress indicator.
	static const int _NUM_ITEMS = 110000;
	static const int _NOTIFY_INTERVAL = 1000;

	// Run the computation associated with this Calculator.
	void run() {
	int i = 0;
	final JsonDecoder decoder = JsonDecoder(
	(dynamic key, dynamic value) {
	if (key is int && i++ % _NOTIFY_INTERVAL == 0)
	onProgressListener(i.toDouble(), _NUM_ITEMS.toDouble());
	return value;
	},
	);
	try {
	final List<dynamic> result = decoder.convert(_data) as List<dynamic>;
	final int n = result.length;
	onResultListener('Decoded $n results');
	} on FormatException catch (e, stack) {
	debugPrint('Invalid JSON file: $e');
	debugPrint('$stack');
	}
	}

	static String _replicateJson(String? data, int count) {
	final StringBuffer buffer = StringBuffer()..write('[');
	for (int i = 0; i < count; i++) {
	buffer.write(data);
	if (i < count - 1)
	buffer.write(',');
	}
	buffer.write(']');
	return buffer.toString();
	}
	}

	// The current state of the calculation.
	enum CalculationState {
	idle,
	loading,
	calculating
	}

	// Structured message to initialize the spawned isolate.
	class CalculationMessage {
	CalculationMessage(this.data, this.sendPort);
	String data;
	SendPort sendPort;
	}

	// A manager for the connection to a spawned isolate.
	//
	// Isolates communicate with each other via ReceivePorts and SendPorts.
	// This class manages these ports and maintains state related to the
	// progress of the background computation.
	class CalculationManager {
	CalculationManager({ required this.onProgressListener, required this.onResultListener })
	: assert(onProgressListener != null),
	assert(onResultListener != null),
	_receivePort = ReceivePort() {
	_receivePort.listen(_handleMessage);
	}

	CalculationState _state = CalculationState.idle;
	CalculationState get state => _state;
	bool get isRunning => _state != CalculationState.idle;

	double _completed = 0.0;
	double _total = 1.0;

	final OnProgressListener onProgressListener;
	final OnResultListener onResultListener;

	// Start the background computation.
	//
	// Does nothing if the computation is already running.
	void start() {
	if (!isRunning) {
	_state = CalculationState.loading;
	_runCalculation();
	}
	}

	// Stop the background computation.
	//
	// Kills the isolate immediately, if spawned. Does nothing if the
	// computation is not running.
	void stop() {
	if (isRunning) {
	_state = CalculationState.idle;
	if (_isolate != null) {
	_isolate!.kill(priority: Isolate.immediate);
	_isolate = null;
	_completed = 0.0;
	_total = 1.0;
	}
	}
	}

	final ReceivePort _receivePort;
	Isolate? _isolate;

	void _runCalculation() {
	// Load the JSON string. This is done in the main isolate because spawned
	// isolates do not have access to the root bundle. However, the loading
	// process is asynchronous, so the UI will not block while the file is
	// loaded.
	rootBundle.loadString('services/data.json').then<void>((String data) {
	if (isRunning) {
	final CalculationMessage message = CalculationMessage(data, _receivePort.sendPort);
	// Spawn an isolate to JSON-parse the file contents. The JSON parsing
	// is synchronous, so if done in the main isolate, the UI would block.
	Isolate.spawn<CalculationMessage>(_calculate, message).then<void>((Isolate isolate) {
	if (!isRunning) {
	isolate.kill(priority: Isolate.immediate);
	} else {
	_state = CalculationState.calculating;
	_isolate = isolate;
	}
	});
	}
	});
	}

	void _handleMessage(dynamic message) {
	if (message is List<double>) {
	_completed = message[0];
	_total = message[1];
	onProgressListener(_completed, _total);
	} else if (message is String) {
	_completed = 0.0;
	_total = 1.0;
	_isolate = null;
	_state = CalculationState.idle;
	onResultListener(message);
	}
	}

	// Main entry point for the spawned isolate.
	//
	// This entry point must be static, and its (single) argument must match
	// the message passed in Isolate.spawn above. Typically, some part of the
	// message will contain a SendPort so that the spawned isolate can
	// communicate back to the main isolate.
	//
	// Static and global variables are initialized anew in the spawned isolate,
	// in a separate memory space.
	static void _calculate(CalculationMessage message) {
	final SendPort sender = message.sendPort;
	final Calculator calculator = Calculator(
	onProgressListener: (double completed, double total) {
	sender.send(<double>[ completed, total ]);
	},
	onResultListener: sender.send,
	data: message.data,
	);
	calculator.run();
	}
	}

	// Main app widget.
	//
	// The app shows a simple UI that allows control of the background computation,
	// as well as an animation to illustrate that the UI does not block while this
	// computation is performed.
	//
	// This is a StatefulWidget in order to hold the CalculationManager and
	// the AnimationController for the running animation.
	class IsolateExampleWidget extends StatefulWidget {
	const IsolateExampleWidget({super.key});

	@override
	IsolateExampleState createState() => IsolateExampleState();
	}

	// Main application state.
	class IsolateExampleState extends State<StatefulWidget> with SingleTickerProviderStateMixin {

	String _status = 'Idle';
	String _label = 'Start';
	String _result = ' ';
	double _progress = 0.0;
	late final AnimationController _animation = AnimationController(
	duration: const Duration(milliseconds: 3600),
	vsync: this,
	)..repeat();
	late final CalculationManager _calculationManager = CalculationManager(
	onProgressListener: _handleProgressUpdate,
	onResultListener: _handleResult,
	);

	@override
	void dispose() {
	_animation.dispose();
	super.dispose();
	}

	@override
	Widget build(BuildContext context) {
	return Material(
	child: Column(
	mainAxisAlignment: MainAxisAlignment.spaceAround,
	children: <Widget>[
	RotationTransition(
	turns: _animation,
	child: Container(
	width: 120.0,
	height: 120.0,
	color: const Color(0xFF882222),
	),
	),
	Opacity(
	opacity: _calculationManager.isRunning ? 1.0 : 0.0,
	child: CircularProgressIndicator(
	value: _progress,
	),
	),
	Text(_status),
	Center(
	child: ElevatedButton(
	onPressed: _handleButtonPressed,
	child: Text(_label),
	),
	),
	Text(_result),
	],
	),
	);
	}

	void _handleProgressUpdate(double completed, double total) {
	_updateState(' ', completed / total);
	}

	void _handleResult(String result) {
	_updateState(result, 0.0);
	}

	void _handleButtonPressed() {
	if (_calculationManager.isRunning)
	_calculationManager.stop();
	else
	_calculationManager.start();
	_updateState(' ', 0.0);
	}

	String _getStatus(CalculationState state) {
	switch (state) {
	case CalculationState.loading:
	return 'Loading...';
	case CalculationState.calculating:
	return 'In Progress';
	case CalculationState.idle:
	return 'Idle';
	}
	}

	void _updateState(String result, double progress) {
	setState(() {
	_result = result;
	_progress = progress;
	_label = _calculationManager.isRunning ? 'Stop' : 'Start';
	_status = _getStatus(_calculationManager.state);
	});
	}
	}

	void main() {
	runApp(const MaterialApp(home: IsolateExampleWidget()));
	}