Convert most of the javascript isolate code into Dart, inject JS code only when

frog/lib/isolate.dart

Index: frog/lib/isolate.dart
diff --git a/frog/lib/isolate.dart b/frog/lib/isolate.dart
index fd52f4e7bb120a915afb15b43ee0e94ee4e6373f..80f210ed03f6cc36828981d8954810502bde88a1 100644
--- a/frog/lib/isolate.dart
+++ b/frog/lib/isolate.dart
@@ -2,6 +2,308 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+/**
+ * A native object that is shared across isolates. This object is visible to all
+ * isolates running on the same worker (either UI or background web worker).
+ *
+ * This is code that is intended to 'escape' the isolate boundaries in order to
+ * implement the semantics of friendly isolates in JavaScript. Without this we
+ * would have been forced to implement more code (including the top-level event
+ * loop) in JavaScript itself.
+ */
+GlobalState get _globalState() native "return \$globalState;";
+set _globalState(GlobalState val) native "\$globalState = val;";
+
+/**
+ * Wrapper that takes the dart entry point and runs it within an isolate. The
+ * frog compiler will inject a call of the form [: startAsIsolate(main); :] when
+ * it determines that this wrapping is needed. For single-isolate applications
+ * (e.g. hello world), this call is not emited.

[mattsh, 2011/11/16 19:09:17]

emitted

[Siggi Cherem (dart-lang), 2011/11/17 02:03:04]

Done.

+ */
+void startAsIsolate(entry) {

[mattsh, 2011/11/16 19:09:17]

startRootIsolate

[Siggi Cherem (dart-lang), 2011/11/17 02:03:04]

Done.

+  _globalState = new GlobalState();
+
+  // Don't start the main loop again, if we are in a worker.
+  if (_globalState.inWorker) return;
+  final entryIsolate = new IsolateContext();

[mattsh, 2011/11/16 19:09:17]

maybe rootContext

[Siggi Cherem (dart-lang), 2011/11/17 02:03:04]

Done.

+  _globalState.rootIsolate = entryIsolate;
+
+  // BUG(5151491): Setting _thisISolate should not be necessary, but because
+  // closures passed to the DOM as event handlers do not bind their isolate
+  // automatically we try to give them a reasonable context to live in by having
+  // a "default" isolate (the first one created).
+  _globalState.currentIsolate = entryIsolate;

[jimhug, 2011/11/16 18:00:45]

I'm glad there's a bug here - this should be fixed.

+
+  entryIsolate.eval(entry);
+  _globalState.topEventLoop.run();
+}
+
+/** Global state associated with the current worker. See [_globalState]. */

[mattsh, 2011/11/16 19:09:17]

mabye call this WorkerState or ThreadState?  It looks like there is one instance
of this per-worker plus one instance for the UI thread, is that right?
Actually reading more, it looks like this merges together fields that are global
to all workers (like 'supportsWorkers') and fields that are per-worker (like
'topEventLoop', and also fields that are only needed by the main thread (like
the 'workers' registy).  Perhaps have separate structures for each of these? 
(e.g. GlobalState,   ThreadState, and MainThreadState)

[Siggi Cherem (dart-lang), 2011/11/17 02:03:04]

yeah - this is a nice suggestion. I'm hope that we only have 2 - thread/worker
and main-thread.

+class GlobalState {
+
+  /** Next available isolate id. */
+  int nextIsolateId = 0;
+
+  /** Worker id associated with this worker. */
+  int currentWorkerId = 0;
+
+  /**
+   * Next available worker id. Only used by the main worker to assign a unique
+   * id to each worker created by it.
+   */
+  int nextWorkerId = 1;
+
+  /** Context for the currently running [Isolate]. */
+  IsolateContext currentIsolate = null;

[mattsh, 2011/11/16 19:09:17]

isolateContext

[Siggi Cherem (dart-lang), 2011/11/17 02:03:04]

Done

+
+  /** Context for the root [Isolate] that first run in this worker. */
+  IsolateContext rootIsolate = null;

[mattsh, 2011/11/16 19:09:17]

rootContext

[Siggi Cherem (dart-lang), 2011/11/17 02:03:04]

Done.

+
+  /** The top-level event loop. */
+  EventLoop topEventLoop;
+
+  /** Whether this program is running in a background worker. */
+  bool inWorker;

[mattsh, 2011/11/16 19:09:17]

inWorker suggests this value might change.  Perhaps calls it 'isWorker'?

[Siggi Cherem (dart-lang), 2011/11/17 02:03:04]

Done.

+
+  /** Whether this program is running in a UI worker. */
+  bool inWindow;
+
+  /** Whether we support spawning workers. */
+  bool supportsWorkers;
+
+  /**
+   * Whether to use web workers when implementing isolates. Set to false for
+   * debugging/testing.
+   */
+  bool get useWorkers() => supportsWorkers;

[Jennifer Messerly, 2011/11/17 02:28:11]

a lot of these properties are redundant?
Should this have a setter (given the comment says "set to false...")?

[Siggi Cherem (dart-lang), 2011/11/17 16:50:11]

For now the 'set to false' is only done by modifying the code by hand. 

A lot of these properties I copied over from the JS version, I was trying not to
change too much how things were initially implemented.

+
+  /**
+   * Whether to use the web-worker JSON-based message serialization protocol,
+   * even if not using web workers. Set to true to always use the web-worker
+   * JSON-based message serialization protocol, e.g. for testing purposes.
+   */
+  bool get useWorkerSerializationProtocol() => useWorkers;

[Jennifer Messerly, 2011/11/17 02:28:11]

Was this an old name? It's reeeeeeallllllyyyy long :)

[Siggi Cherem (dart-lang), 2011/11/17 16:50:11]

I know :) - copied from JS. I'll think of something shorter.

+
+  /**
+   * Registry of isolates. Isolates must be registered if, and only if, receive
+   * ports are alive.  Normally no open receive-ports means that the isolate is
+   * dead, but DOM callbacks could resurrect it.
+   */
+  Map<int, IsolateContext> isolates;
+
+  /** Reference to the main worker. */
+  MainWorker mainWorker;

[mattsh, 2011/11/16 19:09:17]

I think we're using somewhat confusing terminology, we should decide if we want
to call the main window thread to be considered a "worker" or not.  (Elsewhere
we use the term 'worker' to mean everything except the main thread, so we should
decide what it means.)

+
+  /** Registry of active workers. Only used in the main worker. */
+  Map<int, var> workers;

[mattsh, 2011/11/16 19:09:17]

I think let's have a separate structure for fields only needed in the main
thread.

+
+  GlobalState() {
+    topEventLoop = new EventLoop();
+    isolates = {};
+    workers = {};
+    mainWorker = new MainWorker();
+    _nativeInit();
+  }
+
+  void _nativeInit() native @"""
+    this.inWorker = typeof ($globalThis['importScripts']) != 'undefined';
+    this.inWindow = typeof(window) !== 'undefined';
+    this.supportsWorkers = this.inWorker ||
+        ((typeof $globalThis['Worker']) != 'undefined');
+
+    // if workers are supported, treat this as a main worker:
+    if (this.supportsWorkers) {
+      $globalThis.onmessage = function(e) {
+        IsolateNatives._processWorkerMessage(this.mainWorker, e);

[Jennifer Messerly, 2011/11/17 02:28:11]

does the compiler know to emit this if _nativeInit is called?

[Siggi Cherem (dart-lang), 2011/11/17 16:50:11]

It doesn't - fortunately that method is also reachable from 'spawnWorker' below.

+      };
+    }
+  """;
+
+  /**
+   * Close the worker running this code, called when there is nothing else to
+   * run.
+   */
+  void closeWorker() {
+    if (inWorker) {
+      if (!isolates.isEmpty()) return;
+      mainWorker.postMessage(
+          _serializeMessage({'command': 'close'}));
+    } else if (isolates.containsKey(rootIsolate.id) && workers.isEmpty() &&
+               !supportsWorkers && !inWindow) {
+      // This should only trigger when running on the command-line.
+      // We don't want this check to execute in the browser where the isolate
+      // might still be alive due to DOM callbacks.
+      throw new Exception("Program exited with open ReceivePorts.");
+    }
+  }
+}
+
+_serializeMessage(message) {
+  if (_globalState.useWorkerSerializationProtocol) {
+    return new Serializer().traverse(message);
+  } else {
+    return new Copier().traverse(message);
+  }
+}
+
+_deserializeMessage(message) {
+  if (_globalState.useWorkerSerializationProtocol) {
+    return new Deserializer().deserialize(message);
+  } else {
+    // Nothing more to do.
+    return message;
+  }
+}
+
+/** Default worker. */
+class MainWorker {
+  int id = 0;
+  void postMessage(msg) native "return \$globalThis.postMessage(msg);";
+}
+
+/** Context information tracked for each isolate. */
+class IsolateContext {
+  /** Current isolate id. */
+  int id;
+
+  /** Registry of receive ports currently active on this isolate. */
+  Map<int, ReceivePort> ports;
+
+  /** Holds isolate globals (statics and top-level properties). */
+  var isolateStatics; // native object containing all globals of an isolate.
+
+  IsolateContext() {
+    id = _globalState.nextIsolateId++;
+    ports = {};
+    initGlobals();
+  }
+
+  // TODO(sigmund): actually do the initialization too.
+  void initGlobals() native "this.isolateStatics = {};";
+
+  /**
+   * Run [code] in the context of the isolate represented by [this]. Note this
+   * is marked as native because it is called from JavaScript (see $wrap_call in
+   * corejs.dart).
+   */
+  void eval(Function code) native {
+    var old = _globalState.currentIsolate;
+    _globalState.currentIsolate = this;
+    var result = null;
+    try {
+      result = code();
+    } finally {
+      _globalState.currentIsolate = old;
+    }
+    return result;
+  }
+
+  /** Lookup a port registered for this isolate. */
+  ReceivePort lookup(int id) => ports[id];
+
+  /** Register a port on this isolate. */
+  void register(int portId, ReceivePort port)  {
+    if (ports.containsKey(portId)) {
+      throw new Exception("Registry: ports must be registered only once.");
+    }
+    ports[portId] = port;
+    _globalState.isolates[id] = this; // indicate this isolate is active
+  }
+
+  /** Unregister a port on this isolate. */
+  void unregister(int portId) {
+    ports.remove(portId);
+    if (ports.isEmpty()) {
+      _globalState.isolates.remove(id); // indicate this isolate is not active
+    }
+  }
+}
+
+/** Represent the event loop on a javascript thread (DOM or worker). */
+class EventLoop {
+  Queue<IsolateEvent> events;
+
+  EventLoop() : events = new Queue<IsolateEvent>();
+
+  void enqueue(isolate, fn, msg) {
+    events.addLast(new IsolateEvent(isolate, fn, msg));
+  }
+
+  IsolateEvent dequeue() {
+    if (events.isEmpty()) return null;
+    return events.removeFirst();
+  }
+
+  /** Process a single event, if any. */
+  bool runIteration() {
+    final event = dequeue();
+    if (event == null) {
+      _globalState.closeWorker();
+      return false;
+    }
+    event.process();
+    return true;
+  }
+
+  /** Function equivalent to [:window.setTimeout:] when available, or null. */
+  static Function _platformDefer() native """

[mattsh, 2011/11/16 19:09:17]

platformDefer is kind of vague, suggest rename to _setTimeout (which can be null
if the underlying support is not available).  

[Siggi Cherem (dart-lang), 2011/11/17 02:03:04]

Done.

+      return typeof window != 'undefined' ?
+          function(a, b) { window.setTimeout(a, b); } : undefined;
+  """;
+
+  /** 
+   * Runs multiple iterations of the run-loop. If possible, each iteration is
+   * run asynchronously.
+   */
+  void _runHelper() {
+    final setTimeout = _platformDefer();
+    if (setTimeout != null) {
+      // Run each iteration from the browser's top event loop.
+      void next() {
+        if (!runIteration()) return;
+        setTimeout(next, 0);
+      }
+      next();
+    } else {
+      // Run synchronously until no more iterations are available.
+      while (runIteration()) {}
+    }
+  }
+
+  /** 
+   * Call [_runHelper] but ensure that worker exceptions are propragated. Note
+   * this is marked as native because it is called from JavaScript (see
+   * $wrap_call in corejs.dart).
+   */
+  void run() native {
+    if (!_globalState.inWorker) {
+      _runHelper();
+    } else {
+      try {
+        _runHelper();
+      } catch(e) {
+        // TODO(floitsch): try to send stack-trace to the other side.
+        _globalState.mainWorker.postMessage(_serializeMessage(
+            {'command': 'error', 'msg': "" + e }));
+      }
+    }
+  }
+}
+
+/** An event in the top-level event queue. */
+class IsolateEvent {
+  IsolateContext isolate;
+  Function fn;
+  String message;
+
+  IsolateEvent(this.isolate, this.fn, this.message);
+
+  void process() {
+    isolate.eval(fn);
+  }
+}
+
+/** Implementation of a send port on top of JavaScript. */
 class SendPortImpl implements SendPort {
 
   const SendPortImpl(this._workerId, this._isolateId, this._receivePortId);
@@ -10,21 +312,13 @@ class SendPortImpl implements SendPort {
     if (replyTo !== null && !(replyTo is SendPortImpl)) {
       throw "SendPort::send: Illegal replyTo type.";
     }
-    IsolateNatives.sendMessage(_workerId, _isolateId, _receivePortId,
+    IsolateNatives._sendMessage(_workerId, _isolateId, _receivePortId,
         _serializeMessage(message), _serializeMessage(replyTo));
   }
 
-  // TODO(sigmund): get rid of _sendNow
+  // TODO(sigmund): get rid of _sendNow (still used in corelib code)
   void _sendNow(var message, replyTo) { send(message, replyTo); }
 
-  _serializeMessage(message) {
-    if (IsolateNatives.shouldSerialize) {
-      return _IsolateJsUtil._serializeObject(message);
-    } else {
-      return _IsolateJsUtil._copyObject(message);
-    }
-  }
-
   ReceivePortSingleShotImpl call(var message) {
     final result = new ReceivePortSingleShotImpl();
     this.send(message, result.toSendPort());
@@ -51,22 +345,9 @@ class SendPortImpl implements SendPort {
   final int _receivePortId;
   final int _isolateId;
   final int _workerId;
-
-  static _create(int workerId, int isolateId, int receivePortId) native {
-    return new SendPortImpl(workerId, isolateId, receivePortId);
-  }
-  static _getReceivePortId(SendPortImpl port) native {
-    return port._receivePortId;
-  }
-  static _getIsolateId(SendPortImpl port) native {
-    return port._isolateId;
-  }
-  static _getWorkerId(SendPortImpl port) native {
-    return port._workerId;
-  }
 }
 
-
+/** Default factory for receive ports. */
 class ReceivePortFactory {
 
   factory ReceivePort() {
@@ -76,14 +357,13 @@ class ReceivePortFactory {
   factory ReceivePort.singleShot() {
     return new ReceivePortSingleShotImpl();
   }
-
 }
 
-
+/** Implementation of a multi-use [ReceivePort] on top of JavaScript. */
 class ReceivePortImpl implements ReceivePort {
   ReceivePortImpl()
       : _id = _nextFreeId++ {
-    IsolateNatives.registerPort(_id, this);
+    _globalState.currentIsolate.register(_id, this);
   }
 
   void receive(void onMessage(var message, SendPort replyTo)) {
@@ -92,38 +372,25 @@ class ReceivePortImpl implements ReceivePort {
 
   void close() {
     _callback = null;
-    IsolateNatives.unregisterPort(_id);
-  }
-
-  SendPort toSendPort() {
-    return _toNewSendPort();
+    _globalState.currentIsolate.unregister(_id);
   }
 
   /**
    * Returns a fresh [SendPort]. The implementation is not allowed to cache
    * existing ports.
    */
-  SendPort _toNewSendPort() {
+  SendPort toSendPort() {
     return new SendPortImpl(
-        IsolateNatives._currentWorkerId(),
-        IsolateNatives._currentIsolateId(), _id);
+        _globalState.currentWorkerId, _globalState.currentIsolate.id, _id);
   }
 
   int _id;
   Function _callback;
 
   static int _nextFreeId = 1;
-
-  static int _getId(ReceivePortImpl port) native {
-    return port._id;
-  }
-
-  static Function _getCallback(ReceivePortImpl port) native {
-    return port._callback;
-  }
 }
 
-
+/** Implementation of a single-shot [ReceivePort]. */
 class ReceivePortSingleShotImpl implements ReceivePort {
 
   ReceivePortSingleShotImpl() : _port = new ReceivePortImpl() { }
@@ -139,25 +406,16 @@ class ReceivePortSingleShotImpl implements ReceivePort {
     _port.close();
   }
 
-  SendPort toSendPort() {
-    return _toNewSendPort();
-  }
-
-  /**
-   * Returns a fresh [SendPort]. The implementation is not allowed to cache
-   * existing ports.
-   */
-  SendPort _toNewSendPort() {
-    return _port._toNewSendPort();
-  }
+  SendPort toSendPort() => _port.toSendPort();
 
   final ReceivePortImpl _port;
-
 }
 
 final String _SPAWNED_SIGNAL = "spawned";
 
-class IsolateNatives native "IsolateNatives" {
+class IsolateNatives {
+
+  /** JavaScript-specific implementation to spawn an isolate. */
   static Future<SendPort> spawn(Isolate isolate, bool isLight) {
     Completer<SendPort> completer = new Completer<SendPort>();
     ReceivePort port = new ReceivePort.singleShot();
@@ -165,56 +423,225 @@ class IsolateNatives native "IsolateNatives" {
       assert(msg == _SPAWNED_SIGNAL);
       completer.complete(replyPort);
     });
-    _spawn(isolate, isLight, port.toSendPort());
-    if (false) {
-      // TODO(sigmund): delete this code. This is temporarily added because we
-      // are tree-shaking methods that are only reachable from js
-      _IsolateJsUtil._startIsolate(null, null);
-      _IsolateJsUtil._deserializeMessage(null);
-      _IsolateJsUtil._print(null);
+
+    // TODO(floitsch): throw exception if isolate's class doesn't have a
+    // default constructor.
+    if (_globalState.useWorkers && !isLight) {
+      _startWorker(isolate, port.toSendPort());
+    } else {
+      _startNonWorker(isolate, port.toSendPort());
     }
+
     return completer.future;
   }
 
-  static SendPort _spawn(Isolate isolate, bool light, SendPort port) native;
-
-  static bool get shouldSerialize() native;
-
-  static void sendMessage(int workerId, int isolateId, int receivePortId,
-      message, replyTo) native;
-
-  /** Registers an active receive port. */
-  static void registerPort(int id, ReceivePort port) native;
+  static SendPort _startWorker(Isolate runnable, SendPort replyPort) {
+    var factoryName = _getJSConstructorName(runnable);
+    if (_globalState.inWorker) {
+      _globalState.mainWorker.postMessage(_serializeMessage({
+          'command': 'spawn-worker',
+          'factoryName': factoryName,
+          'replyPort': replyPort}));
+    } else {
+      _spawnWorker(factoryName, _serializeMessage(replyPort));
+    }
+  }
 
-  /** Unregister an inactive receive port. */
-  static void unregisterPort(int id) native;
 
-  static int _currentWorkerId() native;
+  /**
+   * The src url for the script tag that loaded this code. Used to create
+   * JavaScript workers.
+   */
+  static String get _thisScript() =>
+      _thisScriptCache != null ? _thisScriptCache : _computeThisScript();
+
+  static String _thisScriptCache;
+
+  // TODO(sigmund): fix - this code should be run synchronously when loading the
+  // script. Running lazily on DOMContentLoaded will yield incorrect results.
+  static String _computeThisScript() native @"""
+    if (!$globalState.supportsWorkers || $globalState.inWorker) return null;
+
+    // TODO(5334778): Find a cross-platform non-brittle way of getting the
+    // currently running script.
+    var scripts = document.getElementsByTagName('script');
+    // The scripts variable only contains the scripts that have already been
+    // executed. The last one is the currently running script.
+    var script = scripts[scripts.length - 1];
+    var src = script.src;
+    if (!src) {
+      // TODO()
+      src = "FIXME:5407062" + "_" + Math.random().toString();
+      script.src = src;
+    }
+    IsolateNatives._thisScriptCache = src;
+    return src;
+  """;
 
-  static int _currentIsolateId() native;
-}
+  /** Starts a new worker with the given URL. */
+  static void _newWorker(url) native "return new Worker(url)";
 
+  /** 
+   * Spawns an isolate in a worker. [factoryName] is the Javascript constructor
+   * name for the isolate entry point class.
+   */
+  static void _spawnWorker(factoryName, serializedReplyPort) {
+    var worker = _newWorker(_thisScript);
+    // TODO(sigmund): make this work.
+    worker.onmessage = function(e) {
+      _processWorkerMessage(worker, e);
+    };
+    var workerId = _globalState.nextWorkerId++;
+    // We also store the id on the worker itself so that we can unregister it.
+    worker.id = workerId;
+    _globalState.workers[workerId] = worker;
+    worker.postMessage(_serializeMessage({
+      'command': 'start',
+      'id': workerId,
+      'replyTo': serializedReplyPort,
+      'factoryName': factoryName }));
+  }
 
-class _IsolateJsUtil native "_IsolateJsUtil" {
-  static void _startIsolate(Isolate isolate, SendPort replyTo) native {
-    ReceivePort port = new ReceivePort();
-    replyTo.send(_SPAWNED_SIGNAL, port.toSendPort());
-    isolate._run(port);
+  /** 
+   * Process messages on a worker, either to control the worker instance or to
+   * pass messages along to the isolate running in the worker.
+   */
+  static void _processWorkerMessage(sender, e) {
+    var msg = _deserializeMessage(e.data);
+    switch (msg['command']) {
+      case 'start':
+        _log("starting worker: " + msg['id'] + " " + msg['factoryName']);
+        _globalState.currentWorkerId = msg['id'];
+        var runnerObject =
+            _allocate(_getJSConstructorFromName(msg['factoryName']));
+        var serializedReplyTo = msg['replyTo'];
+        _globalState.topEventLoop.enqueue(new IsolateContext(), function() {
+          var replyTo = _deserializeMessage(serializedReplyTo);
+          IsolateNatives._startIsolate(runnerObject, replyTo);
+        }, 'worker-start');
+        _globalState.topEventLoop.run();
+        break;
+      case 'spawn-worker':
+        _spawnWorker(msg['factoryName'], msg['replyPort']);
+        break;
+      case 'message':
+        _sendMessage(msg['workerId'], msg['isolateId'], msg['portId'],
+            msg['msg'], msg['replyTo']);
+        _globalState.topEventLoop.run();
+        break;
+      case 'close':
+        _log("Closing Worker");
+        _globalState.workers.remove(sender.id);
+        sender.terminate();
+        _globalState.topEventLoop.run();
+        break;
+      case 'log':
+        _log(msg['msg']);
+        break;
+      case 'print':
+        if (_globalState.inWorker) {
+          _globalState.mainWorker.postMessage(
+              _serializeMessage({'command': 'print', 'msg': msg}));
+        } else {
+          print(msg['msg']);
+        }
+        break;
+      case 'error':
+        throw msg['msg'];
+        break;
+    }
   }
 
-  static void _print(String msg) native {
-    print(msg);
+  /** Log a message, forwarding to the main worker if appropriate. */
+  static _log(msg) {
+    if (_globalState.inWorker) {
+      _globalState.mainWorker.postMessage({'command': 'log', 'msg': msg });
+    } else {
+      try {
+        _consoleLog(msg);
+      } catch(e, trace) {
+        throw new Exception(trace);
+      }
+    }
   }
 
-  static _copyObject(obj) native {
-    return new Copier().traverse(obj);
+  static void _consoleLog(msg) native "\$globalThis.console.log(msg);";
+
+
+  /** 
+   * Extract the constructor of runnable, so it can be allocated in another
+   * isolate.
+   */
+  static var _getJSConstructor(Isolate runnable) native """
+    return runnable.constructor;
+  """;
+
+  /** Extract the constructor name of a runnable */
+  // TODO(sigmund): find a browser-generic way to support this.
+  static var _getJSConstructorName(Isolate runnable) native """
+    return runnable.constructor.name;
+  """;
+
+  /** Find a constructor given it's name. */
+  static var _getJSConstructorFromName(String factoryName) native """
+    return \$globalThis[factoryName];
+  """;
+
+  /** Create a new JavasSript object instance given it's constructor. */
+  static var _allocate(var ctor) native "return new ctor();";
+
+  /** Starts a non-worker isolate. */
+  static SendPort _startNonWorker(Isolate runnable, SendPort replyTo) {
+    // Spawn a new isolate and create the receive port in it.
+    final spawned = new IsolateContext();
+
+    // Instead of just running the provided runnable, we create a
+    // new cloned instance of it with a fresh state in the spawned
+    // isolate. This way, we do not get cross-isolate references
+    // through the runnable.
+    final ctor = _getJSConstructor(runnable);
+    _globalState.topEventLoop.enqueue(spawned, function() {
+      _startIsolate(_allocate(ctor), replyTo);
+    }, 'nonworker start');
   }
 
-  static _serializeObject(obj) native {
-    return new Serializer().traverse(obj);
+  /** Given a ready-to-start runnable, start running it. */
+  static void _startIsolate(Isolate isolate, SendPort replyTo) {
+    ReceivePort port = new ReceivePort();
+    replyTo.send(_SPAWNED_SIGNAL, port.toSendPort());
+    isolate._run(port);
   }
 
-  static _deserializeMessage(message) native {
-    return new Deserializer().deserialize(message);
+  static void _sendMessage(int workerId, int isolateId, int receivePortId,
+      message, replyTo) {
+    // Both the message and the replyTo are already serialized.
+    if (workerId == _globalState.currentWorkerId) {
+      var isolate = _globalState.isolates[isolateId];
+      if (isolate == null) return;  // Isolate has been closed.
+      var receivePort = isolate.lookup(receivePortId);
+      if (receivePort == null) return;  // ReceivePort has been closed.
+      _globalState.topEventLoop.enqueue(isolate, () {
+        if (receivePort._callback != null) {
+          receivePort._callback(
+            _deserializeMessage(message), _deserializeMessage(replyTo));
+        }
+      }, 'receive ' + message);
+    } else {
+      var worker;
+      // communication between workers go through the main worker
+      if (_globalState.inWorker) {
+        worker = _globalState.mainWorker;
+      } else {
+        // TODO(sigmund): make sure this works
+        worker = _globalState.workers[workerId];
+      }
+      worker.postMessage(_serializeMessage({
+          'command': 'message',
+          'workerId': workerId,
+          'isolateId': isolateId,
+          'portId': receivePortId,
+          'msg': message,
+          'replyTo': replyTo }));
+    }
   }
 }