Generailze reusuable worker

lib/src/embedded/isolate_dispatcher.dart

@@ -11,7 +11,7 @@ import 'package:stream_channel/stream_channel.dart';
 
 import 'concurrency.dart' if (dart.library.js) 'js/concurrency.dart';
 import 'embedded_sass.pb.dart';
-import 'isolate_main.dart';
+import 'isolate_main.dart' if (dart.library.js) 'js/isolate_main.dart';
 import 'reusable_isolate.dart' if (dart.library.js) 'js/reusable_isolate.dart';
 import 'util/proto_extensions.dart';
 import 'utils.dart';

lib/src/embedded/js/isolate_main.dart

@@ -0,0 +1,14 @@
+// Copyright 2024 Google Inc. Use of this source code is governed by an
+// MIT-style license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'dart:js_interop';
+
+import 'js.dart';
+
+@JS('process.argv')
+external JSArray<JSAny?> get _argv;
+
+(String, JSArray<JSString>) isolateMain() {
+  return (_argv[1]! as String, _argv.slice(2) as JSArray<JSString>);
+}

lib/src/embedded/js/js.dart

@@ -0,0 +1,14 @@
+// Copyright 2024 Google Inc. Use of this source code is governed by an
+// MIT-style license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'dart:js_interop';
+
+extension JSTypedArrayExtension on JSTypedArray {
+  external JSArrayBuffer get buffer;
+}
+
+extension JSArrayExtension<T extends JSAny?> on JSArray<T> {
+  external T operator [](int index);
+  external JSArray<T> slice([int start, int end]);
+}

lib/src/embedded/js/reusable_isolate.dart

@@ -7,11 +7,14 @@ import 'dart:js_interop';
 import 'dart:typed_data';
 
 import '../../io.dart';
+import 'js.dart';
 import 'sync_message_port.dart';
 import 'worker_threads.dart';
 
-@JS('process.argv')
-external JSArray<JSString> get _argv;
+/// The entrypoint for a [ReusableIsolate].
+///
+/// This must return a Record of filename and argv for creating the Worker.
+typedef ReusableIsolateEntryPoint = (String, JSArray<JSAny?>) Function();
 
 class ReusableIsolate {
   /// The worker.
@@ -33,17 +36,17 @@ class ReusableIsolate {
       this._worker, this._sendPort, this._receivePort, this._subscription);
 
   /// Spawns a [ReusableIsolate] that runs the the entrypoint script.
-  static Future<ReusableIsolate> spawn(Function unused,
+  static Future<ReusableIsolate> spawn(ReusableIsolateEntryPoint entryPoint,
       {Function? onError}) async {
+    var (filename, argv) = entryPoint();
     var channel = SyncMessagePort.createChannel();
-    var argv = _argv.toDart;
     var worker = Worker(
-        argv[1].toDart,
+        filename,
         WorkerOptions(
             workerData: channel.port2,
             transferList: [channel.port2].toJS,
-            argv: argv.sublist(2).toJS));
-    worker.on(
+            argv: argv));
+    worker.once(
         'exit',
         (int code) {
           // Worker exit code 1 means it is killed by worker.terminate()

lib/src/embedded/js/sync_receive_port.dart

@@ -7,6 +7,7 @@ import 'dart:typed_data';
 
 import '../sync_receive_port.dart';
 import 'isolate.dart';
+import 'js.dart';
 import 'sync_message_port.dart';
 import 'worker_threads.dart';
 

lib/src/embedded/js/worker_threads.dart

@@ -4,10 +4,6 @@
 
 import 'dart:js_interop';
 
-extension JSUint8ArrayExt on JSUint8Array {
-  external JSObject get buffer;
-}
-
 @JS('worker_threads.isMainThread')
 external bool get isMainThread;
 
@@ -17,14 +13,14 @@ external JSAny? get workerData;
 @JS('worker_threads.Worker')
 extension type Worker._(JSObject _) implements JSObject {
   external Worker(String filename, WorkerOptions options);
-  external void on(String type, JSFunction listener);
+  external void once(String type, JSFunction listener);
   external void terminate();
 }
 
 @JS()
 extension type WorkerOptions._(JSObject _) implements JSObject {
   external WorkerOptions(
-      {JSArray<JSAny> argv,
+      {JSArray<JSAny?> argv,
       JSObject env,
       bool eval,
       JSArray<JSString> execArgv,
@@ -35,7 +31,7 @@ extension type WorkerOptions._(JSObject _) implements JSObject {
       bool trackUnmanagedFds,
       JSArray<JSAny> transferList,
       ResourceLimits resourceLimits});
-  external JSArray<JSAny> get argv;
+  external JSArray<JSAny?> get argv;
   external JSObject get env;
   external bool get eval;
   external JSArray<JSString> get execArgv;