Create isolates in a separate thread.

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 238 matching lines @@
       void entryPoint(message), var message, { bool paused: false }) {
     // `paused` isn't handled yet.
     RawReceivePort readyPort;
     try {
       // The VM will invoke [_startIsolate] with entryPoint as argument.
       readyPort = new RawReceivePort();
       _spawnFunction(readyPort.sendPort, entryPoint, message);
       Completer completer = new Completer<Isolate>.sync();
       readyPort.handler = (readyMessage) {
         readyPort.close();
-        assert(readyMessage is List);
-        assert(readyMessage.length == 2);
-        SendPort controlPort = readyMessage[0];
-        List capabilities = readyMessage[1];
-        completer.complete(new Isolate(controlPort,
-                                       pauseCapability: capabilities[0],
-                                       terminateCapability: capabilities[1]));
+        if (readyMessage is String) {
+          // We encountered an error starting the new isolate.
+          completer.completeError(new IsolateSpawnException(
+              "Unable to spawn child isolate:\n${readyMessage}"));
+        } else {
+          assert(readyMessage is List);

[Cutch, 2014/08/27 18:18:43]

These asserts will only trigger in checked mode. Should you do:

if (readyMessage is String) {
  completer.completeError...
} else if ((readyMessage is List) && (readyMessage.length == 2)) {
  completer.complete
} else {
  completer.completeError...
}

?

[turnidge, 2014/08/27 19:28:59]

Done.

On 2014/08/27 18:18:43, Cutch wrote:

+          assert(readyMessage.length == 2);
+          SendPort controlPort = readyMessage[0];
+          List capabilities = readyMessage[1];
+          completer.complete(new Isolate(controlPort,
+                                         pauseCapability: capabilities[0],
+                                         terminateCapability: capabilities[1]));
+        }
       };
       return completer.future;
     } catch (e, st) {
       if (readyPort != null) {
         readyPort.close();
       }
       return new Future<Isolate>.error(e, st);
     };
   }
 
   /* patch */ static Future<Isolate> spawnUri(
       Uri uri, List<String> args, var message, { bool paused: false }) {
     // `paused` isn't handled yet.
     RawReceivePort readyPort;
     try {
       // The VM will invoke [_startIsolate] and not `main`.
       readyPort = new RawReceivePort();
       _spawnUri(readyPort.sendPort, uri.toString(), args, message);
       Completer completer = new Completer<Isolate>.sync();
       readyPort.handler = (readyMessage) {
         readyPort.close();
-        assert(readyMessage is List);
-        assert(readyMessage.length == 2);
-        SendPort controlPort = readyMessage[0];
-        List capabilities = readyMessage[1];
-        completer.complete(new Isolate(controlPort,
-                                       pauseCapability: capabilities[0],
-                                       terminateCapability: capabilities[1]));
+        if (readyMessage is String) {
+          // We encountered an error starting the new isolate.
+          completer.completeError(new IsolateSpawnException(
+              "Unable to spawn child isolate:\n${readyMessage}"));
+        } else {
+          assert(readyMessage is List);
+          assert(readyMessage.length == 2);
+          SendPort controlPort = readyMessage[0];
+          List capabilities = readyMessage[1];
+          completer.complete(new Isolate(controlPort,

[Cutch, 2014/08/27 18:18:43]

Duplicate code from above? Perhaps you can extract this entire closure into a
utility function.

[turnidge, 2014/08/27 19:28:59]

Extracted common code into new function spawnCommon.

+                                         pauseCapability: capabilities[0],
+                                         terminateCapability: capabilities[1]));
+        }
       };
       return completer.future;
     } catch (e, st) {
       if (readyPort != null) {
         readyPort.close();
       }
       return new Future<Isolate>.error(e, st);
     };
     return completer.future;
   }
@@ skipping 53 matching lines @@
   }
 
   /* patch */ void addErrorListener(SendPort port) {
     throw new UnsupportedError("addErrorListener");
   }
 
   /* patch */ void removeErrorListener(SendPort port) {
     throw new UnsupportedError("removeErrorListener");
   }
 }