Isolate.spawn{Uri} only reports errors asynchronously.

runtime/lib/isolate_patch.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // 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.
 
 import "dart:collection" show HashMap;
 
 patch class ReceivePort {
   /* patch */ factory ReceivePort() = _ReceivePortImpl;
 
   /* patch */ factory ReceivePort.fromRawReceivePort(RawReceivePort rawPort) =
@@ skipping 39 matching lines @@
 
   close() {
     _rawPort.close();
     _controller.close();
   }
 
   final RawReceivePort _rawPort;
   StreamController _controller;
 }
 
+typedef void ImmediateCallback();
+
+/// The callback that has been registered through `scheduleImmediate`.
+ImmediateCallback _pendingImmediateCallback;
+
+/// The closure that should be used as scheduleImmediateClosure, when the VM
+/// is responsible for the event loop.
+void _isolateScheduleImmediate(void callback()) {
+  assert(_pendingImmediateCallback == null);
+  _pendingImmediateCallback = callback;
+}
+
+/// Provide closurized access to _isolateScheduleImmediate.
+/// This makes it easier for embedders to set the scheduleImmediate closure.
+Function get _isolateScheduleImmediateClosure => _isolateScheduleImmediate;
+
+/// The embedder can execute this function to get hold of
+/// [_isolateScheduleImmediate] above.
+Function _getIsolateScheduleImmediateClosure() {
+  return _isolateScheduleImmediate;
+}
+
 class _RawReceivePortImpl implements RawReceivePort {
   factory _RawReceivePortImpl() native "RawReceivePortImpl_factory";
 
   close() {
     _portMap.remove(_id);
     _closeInternal(_id);
   }
 
   SendPort get sendPort {
     return new _SendPortImpl(_id);
@@ skipping 15 matching lines @@
 
   // Called from the VM to retrieve the RawReceivePort for a message.
   static _RawReceivePortImpl _lookupReceivePort(int id) {
     return _portMap[id];
   }
 
   // Called from the VM to dispatch to the handler.
   static void _handleMessage(
       _RawReceivePortImpl port, int replyId, var message) {
     assert(port != null);
+    // TODO(floitsch): this relies on the fact that any exception aborts the

[Lasse Reichstein Nielsen, 2013/11/27 11:41:28]

Bugnumber for catching uncaught exceptions?

[floitsch, 2013/11/27 13:57:06]

I have added 8875.

+    // VM. Once we have non-fatal global exceptions we need to catch errors
+    // so that we can run the immediate callbacks.
     port._handler(message);
+    if (_pendingImmediateCallback != null) {
+      var callback = _pendingImmediateCallback;
+      _pendingImmediateCallback = null;
+      callback();
+    }
   }
 
   // Call into the VM to close the VM maintained mappings.
   static _closeInternal(int id) native "RawReceivePortImpl_closeInternal";
 
   void set handler(Function newHandler) {
     this._handler = newHandler;
   }
 
   final int _id;
@@ skipping 102 matching lines @@
       // The VM will invoke [_startIsolate] with entryPoint as argument.
       SendPort controlPort = _spawnFunction(entryPoint);
       RawReceivePort readyPort = new RawReceivePort();
       controlPort.send([readyPort.sendPort, message]);
       readyPort.handler = (readyMessage) {
         assert(readyMessage == 'started');
         readyPort.close();
         completer.complete(new Isolate._fromControlPort(controlPort));
       };
     } catch(e, st) {
-      // TODO(14718): we want errors to go into the returned future.
-      rethrow;
+      // Don't complete immediately with an error, since the caller didn't
+      // yet have the time to install an error handler.
+      scheduleMicrotask(() {
+        completer.completeError(e, st);

[Lasse Reichstein Nielsen, 2013/11/27 11:41:28]

Could we add this to the head of the queue instead of at the end?

[floitsch, 2013/11/27 13:57:06]

The current implementation is consistent with a non-sync completer.

+      });
     };
     return completer.future;
   }
 
   /* patch */ static Future<Isolate> spawnUri(
       Uri uri, List<String> args, var message) {
     Completer completer = new Completer<Isolate>.sync();
     try {
       // The VM will invoke [_startIsolate] and not `main`.
       SendPort controlPort = _spawnUri(uri.toString());
       RawReceivePort readyPort = new RawReceivePort();
       controlPort.send([readyPort.sendPort, args, message]);
       readyPort.handler = (readyMessage) {
         assert(readyMessage == 'started');
         readyPort.close();
         completer.complete(new Isolate._fromControlPort(controlPort));
       };
     } catch(e, st) {
-      // TODO(14718): we want errors to go into the returned future.
-      rethrow;
+      // Don't complete immediately with an error, since the caller didn't
+      // yet have the time to install an error handler.
+      scheduleMicrotask(() {
+        completer.completeError(e, st);
+      });
     };
     return completer.future;
   }
 
   static final RawReceivePort _self = _mainPort;
   static RawReceivePort get _mainPort native "Isolate_mainPort";
 
   static SendPort _spawnFunction(Function topLevelFunction)
       native "Isolate_spawnFunction";
 
   static SendPort _spawnUri(String uri) native "Isolate_spawnUri";
 }