Add compute api to js engine.

lib/foundation/js_pool.dart

@@ -0,0 +1,163 @@
+import 'dart:async';
+import 'dart:isolate';
+import 'package:flutter/services.dart';
+import 'package:flutter_qjs/flutter_qjs.dart';
+import 'package:venera/foundation/js_engine.dart';
+import 'package:venera/foundation/log.dart';
+
+class JSPool {
+  static final int _maxInstances = 4;
+  final List<IsolateJsEngine> _instances = [];
+  bool _isInitializing = false;
+
+  static final JSPool _singleton = JSPool._internal();
+  factory JSPool() {
+    return _singleton;
+  }
+  JSPool._internal();
+
+  Future<void> init() async {
+    if (_isInitializing) return;
+    _isInitializing = true;
+    var jsInitBuffer = await rootBundle.load("assets/init.js");
+    var jsInit = jsInitBuffer.buffer.asUint8List();
+    for (int i = 0; i < _maxInstances; i++) {
+      _instances.add(IsolateJsEngine(jsInit));
+    }
+    _isInitializing = false;
+  }
+
+  Future<dynamic> execute(String jsFunction, List<dynamic> args) async {
+    await init();
+    var selectedInstance = _instances[0];
+    for (var instance in _instances) {
+      if (instance.pendingTasks < selectedInstance.pendingTasks) {
+        selectedInstance = instance;
+      }
+    }
+    return selectedInstance.execute(jsFunction, args);
+  }
+}
+
+class _IsolateJsEngineInitParam {
+  final SendPort sendPort;
+
+  final Uint8List jsInit;
+
+  _IsolateJsEngineInitParam(this.sendPort, this.jsInit);
+}
+
+class IsolateJsEngine {
+  Isolate? _isolate;
+
+  SendPort? _sendPort;
+  ReceivePort? _receivePort;
+
+  int _counter = 0;
+  final Map<int, Completer<dynamic>> _tasks = {};
+
+  bool _isClosed = false;
+
+  int get pendingTasks => _tasks.length;
+
+  IsolateJsEngine(Uint8List jsInit) {
+    _receivePort = ReceivePort();
+    _receivePort!.listen(_onMessage);
+    Isolate.spawn(_run, _IsolateJsEngineInitParam(_receivePort!.sendPort, jsInit));
+  }
+
+  void _onMessage(dynamic message) {
+    if (message is SendPort) {
+      _sendPort = message;
+    } else if (message is TaskResult) {
+      final completer = _tasks.remove(message.id);
+      if (completer != null) {
+        if (message.error != null) {
+          completer.completeError(message.error!);
+        } else {
+          completer.complete(message.result);
+        }
+      }
+    } else if (message is Exception) {
+      Log.error("IsolateJsEngine", message.toString());
+      for (var completer in _tasks.values) {
+        completer.completeError(message);
+      }
+      _tasks.clear();
+      close();
+    }
+  }
+
+  static void _run(_IsolateJsEngineInitParam params) async {
+    var sendPort = params.sendPort;
+    final port = ReceivePort();
+    sendPort.send(port.sendPort);
+    final engine = JsEngine();
+    try {
+      JsEngine.cacheJsInit(params.jsInit);
+      await engine.init();
+    }
+    catch(e, s) {
+      sendPort.send(Exception("Failed to initialize JS engine: $e\n$s"));
+      return;
+    }
+    await for (final message in port) {
+      if (message is Task) {
+        try {
+          final jsFunc = engine.runCode(message.jsFunction);
+          if (jsFunc is! JSInvokable) {
+            throw Exception("The provided code does not evaluate to a function.");
+          }
+          final result = jsFunc.invoke(message.args);
+          jsFunc.free();
+          sendPort.send(TaskResult(message.id, result, null));
+        } catch (e) {
+          sendPort.send(TaskResult(message.id, null, e.toString()));
+        }
+      }
+    }
+  }
+
+  Future<dynamic> execute(String jsFunction, List<dynamic> args) async {
+    if (_isClosed) {
+      throw Exception("IsolateJsEngine is closed.");
+    }
+    while (_sendPort == null) {
+      await Future.delayed(const Duration(milliseconds: 10));
+    }
+    final completer = Completer<dynamic>();
+    final taskId = _counter++;
+    _tasks[taskId] = completer;
+    final task = Task(taskId, jsFunction, args);
+    _sendPort?.send(task);
+    return completer.future;
+  }
+
+  void close() async {
+    if (!_isClosed) {
+      _isClosed = true;
+      while (_tasks.isNotEmpty) {
+        await Future.delayed(const Duration(milliseconds: 100));
+      }
+      _receivePort?.close();
+      _isolate?.kill(priority: Isolate.immediate);
+      _isolate = null;
+    }
+  }
+}
+
+class Task {
+  final int id;
+  final String jsFunction;
+  final List<dynamic> args;
+
+  const Task(this.id, this.jsFunction, this.args);
+}
+
+class TaskResult {
+  final int id;
+  final Object? result;
+  final String? error;
+
+  const TaskResult(this.id, this.result, this.error);
+}