flutter-handling-concurrency

$2a

Decision Matrix: Async vs. Isolates

Apply the following conditional logic to determine the correct concurrency approach:

• If the task is I/O bound (e.g., HTTP request, database read) -> **Use async/await** on the Main Isolate.

• If the task is CPU-bound but executes quickly (< 16ms) -> **Use async/await** on the Main Isolate.

• If the task is CPU-bound, takes significant time, and runs once (e.g., parsing a massive JSON payload) -> **Use Isolate.run()**.

• If the task requires continuous or repeated background processing with multiple messages passed over time -> **Use Isolate.spawn() with ReceivePort and SendPort**.

Workflows

Implementing Standard Asynchronous UI

Use this workflow to fetch and display non-blocking asynchronous data.

Task Progress:

• Mark the data-fetching function with the async keyword.

• Return a Future<T> from the function.

• Use the await keyword to yield execution until the operation completes.

• Wrap the UI component in a FutureBuilder<T> (or StreamBuilder for streams).

• Handle ConnectionState.waiting, hasError, and hasData states within the builder.

• Run validator -> review UI for loading indicators -> fix missing states.

Offloading Short-Lived Heavy Computation

Use this workflow for one-off, CPU-intensive tasks using Dart 2.19+.

Task Progress:

• Identify the CPU-bound operation blocking the Main Isolate.

• Extract the computation into a standalone callback function.

• Ensure the callback function signature accepts exactly one required, unnamed argument (as per specific architectural constraints).

• Invoke Isolate.run() passing the callback.

• await the result of Isolate.run() in the Main Isolate.

• Assign the returned value to the application state.

Establishing Long-Lived Worker Isolates

Use this workflow for persistent background processes requiring continuous bidirectional communication.

Task Progress:

• Instantiate a ReceivePort on the Main Isolate to listen for messages.

• Spawn the worker isolate using Isolate.spawn(), passing the ReceivePort.sendPort as the initial message.

• In the worker isolate, instantiate its own ReceivePort.

• Send the worker's SendPort back to the Main Isolate via the initial port.

• Store the worker's SendPort in the Main Isolate for future message dispatching.

• Implement listeners on both ReceivePort instances to handle incoming messages.

• Run validator -> review memory leaks -> ensure ports are closed when the isolate is no longer needed.

Examples

Example 1: Asynchronous UI with FutureBuilder

// 1. Define the async operation

Future<String> fetchUserData() async {

  await Future.delayed(const Duration(seconds: 2)); // Simulate network I/O

  return "User Data Loaded";

}

// 2. Consume in the UI

Widget build(BuildContext context) {

  return FutureBuilder<String>(

    future: fetchUserData(),

    builder: (context, snapshot) {

      if (snapshot.connectionState == ConnectionState.waiting) {

        return const CircularProgressIndicator();

      } else if (snapshot.hasError) {

        return Text('Error: ${snapshot.error}');

      } else {

        return Text('Result: ${snapshot.data}');

      }

    },

  );

}

Example 2: Short-Lived Isolate ( Isolate.run )

import 'dart:isolate';

import 'dart:convert';

// 1. Define the heavy computation callback

// Note: Adhering to the strict single-argument signature requirement.

List<dynamic> decodeHeavyJson(String jsonString) {

  return jsonDecode(jsonString) as List<dynamic>;

}

// 2. Offload to a worker isolate

Future<List<dynamic>> processDataInBackground(String rawJson) async {

  // Isolate.run spawns the isolate, runs the computation, returns the value, and exits.

  final result = await Isolate.run(() => decodeHeavyJson(rawJson));

  return result;

}

Example 3: Long-Lived Isolate ( ReceivePort / SendPort )

import 'dart:isolate';

class WorkerManager {

  late SendPort _workerSendPort;

  final ReceivePort _mainReceivePort = ReceivePort();

  Isolate? _isolate;

  Future<void> initialize() async {

    // 1. Spawn isolate and pass the Main Isolate's SendPort

    _isolate = await Isolate.spawn(_workerEntry, _mainReceivePort.sendPort);

    // 2. Listen for messages from the Worker Isolate

    _mainReceivePort.listen((message) {

      if (message is SendPort) {

        // First message is the Worker's SendPort

        _workerSendPort = message;

        _startCommunication();

      } else {

        // Subsequent messages are data payloads

        print('Main Isolate received: $message');

      }

    });

  }

  void _startCommunication() {

    // Send data to the worker

    _workerSendPort.send("Process this data");

  }

  // 3. Worker Isolate Entry Point

  static void _workerEntry(SendPort mainSendPort) {

    final workerReceivePort = ReceivePort();

    // Send the Worker's SendPort back to the Main Isolate

    mainSendPort.send(workerReceivePort.sendPort);

    // Listen for incoming tasks

    workerReceivePort.listen((message) {

      print('Worker Isolate received: $message');

      // Perform work and send result back

      final result = "Processed: $message";

      mainSendPort.send(result);

    });

  }

  void dispose() {

    _mainReceivePort.close();

    _isolate?.kill();

  }

}