isolate_manager 4.2.2

An easy way to create multiple isolates for a function, also keep it active to send and receive data multiple times (also supports Worker on Web).

Isolate Manager

Features

• An easy way to create multiple isolates for a function and keep it active to send and receive data multiple times.

• Supports Worker on the Web (Worker is the real Isolate on the Web). The plugin will use Future (and Stream) if Worker is unavailable in the working browser or is not configured.

• Multiple compute operations are allowed because the plugin will queue the input data and send it to a free isolate later.

• Supports try-catch blocks.

• If you don't need to control your own function, you can use isolates_helper - a simpler version of this package that allows you to compute with multiple functions.

Basic Usage (Use built-in function)

There are multiple ways to use this package. The only thing to notice is that the function has to be a static or top-level function to work.

Step 1: Create a top-level or static function

Future<Map<String, dynamic>> fetchAndDecode(String url) async {
  final response = await http.Client().get(Uri.parse(url));
  return jsonDecode(response.body);
}

Step 2: Create an IsolateManager instance for that function

final isolateFetchAndDecode = IsolateManager.create(
  fetchAndDecode, // Function you want to compute
  concurrent: 4, // Number of concurrent isolates. Default is 1
);

Step 3 [Optional]: Initialize the instance; this step is not required because it's automatically called when you use .compute for the first time

await isolateManager.start();

You can also run this method when creating the instance:

final isolateManager = IsolateManager.create(
  fetchAndDecode, // Function you want to compute
  concurrent: 4, // Number of concurrent isolates. Default is 1
)..start();

Step 4: Send and receive data

final result = await isolateManager.compute('https://path/to/json.json');

You can send even more times than concurrent because the plugin will queue the input data and send it to a free isolate later.

You can listen to the result as a stream:

isolateManager.stream.listen((result) => print(result));

Build your widget with StreamBuilder:

StreamBuilder(
  stream: isolateManager.stream,
  builder: (context, snapshot) {
    if (!snapshot.hasData) {
      return const Center(
        child: CircularProgressIndicator(),
      );
    }
    return Text('Data: ${snapshot.data}');
  },
),

Step 5: Restart the IsolateManager if needed

await isolateManager.restart();

Step 6: Stop IsolateManager when it finishes work

await isolateManager.stop();

Worker Configuration

Step 1: Create a Worker file

Create a worker.dart file with this content

import 'package:isolate_manager/isolate_manager.dart';

main() {
  // The function `fetchAndDecode` MUST NOT depend on any Flutter library
  IsolateFunctionHelper.workerFunction(fetchAndDecode);
}

Step 2: Compile to JS

Run dart compile js worker.dart -o worker.js -O4 to compile Dart to JS (The flag -O4 is the obfuscated level of JS, the lowest value is -O0 and the highest value is -O4)

Step 3: Copy to the Web folder

Copy worker.js to the Web folder (the same folder with index.html)

Step 4: Add it to the IsolateManager

Update the isolateManager like below

final isolateManager = IsolateManager.create(
    fetchAndDecode,
    workerName: 'worker', // The name of the file, don't need to add the extension
  );

Now the plugin will handle all other action to make the real isolate works on Web.

Note: If you want to use Worker more effectively, convert all parameters and results to JSON (or String) before sending them.

Advanced Usage (Use your own function)

You can control everything with this method when you want to create multiple isolates for a function. With this method, you can also do one-time stuff when the isolate is started or each-time stuff when you call compute or sendMessage.

Step 1: Create a function of this form

Let it automatically handles the result and the Exception:

void customIsolateFunction(dynamic params) {
  IsolateFunctionHelper.customFunction<int, int>(
    params,
    onEvent: (controller, message) {
      /* This event will be executed every time the `message` is received from the main isolate */
      return fetchAndDecode(message);
    },
    onInitial: (controller, initialParams) {
       /* This event will be excuted before all other events and should not be a `Future` event */
    },
    onDispose: (controller) {
       /* This event will be excuted after all other events and should not be a `Future` event */
    },
  );
}

Handle the result and the Exception by your self:

void customIsolateFunction(dynamic params) {
  IsolateFunctionHelper.customFunction<int, int>(
    params,
    onEvent: (controller, message) async {
      /* This event will be executed every time the `message` is received from the main isolate */
      try {
        final result = await fetchAndDecode(message);
        controller.sendResult(result);
      } catch (err, stack) {
        controller.sendResultError(IsolateException(err, stack));
      }

      // Just returns something that unused to complete this method.
      return 0;
    },
    onInitial: (controller, initialParams) {
       /* This event will be executed before all the other events and should not be a `Future` event */
    },
    onDispose: (controller) {
       /* This event will be executed after all the other events and should not be a `Future` event */
    },
    autoHandleException: false,
    autoHandleResult: false,
  );
}

Step 2: Create an IsolateManager instance for your own function

final isolateManager = IsolateManager.createCustom(
    customIsolateFunction,
    initialParams: 'This is initialParams',
    debugMode: true,
  );

Step 3:

Now you can use everything as above from this step.

Additional features

• You can use try-catch to catch exceptions:

try {
  final result = await isolateManager.compute('https://path/to/json.json');
} on Exception catch (e1) {
  print(e1);
} catch (e2) {
  print(e2);
}

• You can even manage the final result by using this callback, useful when you create your own function that needs to send the progress value before returning the final result (look at the example in the method isolateProgressFunction for more details):

final result = await isolateManager.compute('https://path/to/json.json',
      callback: (value) {
        // Condition to recognize the progress value. Ex:
        final decoded = jsonDecode(value);
        if (decoded.containsKey('progress')) {
          print(decoded['progress']);

          // Mark this value as not the final result
          return false;
        }

        print('The final result is: $value');
        // Mark this value as the final result and send it into the `result`.
        return true;
      }
    )

Additional

• Use queuesLength to get the current number of queued computation.

• Use ensureStarted to able to wait for the start method to finish when you want to call the start method manually without await and wait for it later.

• Use isStarted to check if the start method is completed or not.

• The result that you get from the isolate (or Worker) is sometimes different from the result that you want to get from the return type in the main app, you can use converter and workerConverter parameters to convert the result received from the Isolate (converter) and Worker (workerConverter). Example:

  final isolateManager = IsolateManager.create(
    convertToMap,
    // Ex: 'worker' if the name is 'worker.js'
    workerName: 'worker',
    // Convert the data from worker to fix the issue related to the different data type between dart and js
    workerConverter: (result) {
      final Map<int, double> convert = {};
  
      // Convert Map<String, String> (received from Worker) to Map<int, double>
      final decodedMap = jsonDecode(result) as Map;
      decodedMap.forEach((key, value) => convert.addAll({int.parse(key): double.parse(value)}));
  
      return convert;
    },
  );
  

  Data flow: Main -> Isolate or Worker -> Converter -> Result

• If you want to use Worker more effectively, convert all parameters and results to JSON (or String) before sending them.

Contributions

• If you encounter any problems or feel the library is missing a feature, feel free to open an issue. Pull requests are also welcome.

• If you like my work or the free stuff on this channel and want to say thanks, or encourage me to do more, you can buy me a coffee. Thank you so much!
  

To-do list

• Find the best way to prevent using dart compile js.