Start 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;
 import "dart:_internal";
 
 patch class ReceivePort {
   /* patch */ factory ReceivePort() = _ReceivePortImpl;
 
@@ skipping 266 matching lines @@
       void entryPoint(message), var message,
       {bool paused: false, bool errorsAreFatal,
        SendPort onExit, SendPort onError}) {
     // `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,
                      paused, errorsAreFatal, onExit, onError);
-      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]));
-      };
-      return completer.future;
+      return _spawnCommon(readyPort);
     } 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,
@@ skipping 12 matching lines @@
       var packageRootString =
           (packageRoot == null) ? null : packageRoot.toString();
       var packagesList = null;
 
       _spawnUri(readyPort.sendPort, uri.toString(),
                 args, message,
                 paused, onExit, onError,
                 errorsAreFatal, checked,
                 null, /* environment */
                 packageRootString, packagesList);
-      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]));
-      };
-      return completer.future;
+      return _spawnCommon(readyPort);
     } catch (e, st) {
       if (readyPort != null) {
         readyPort.close();
       }
       return new Future<Isolate>.error(e, st);
     }
+  }
+
+  static Future<Isolate> _spawnCommon(RawReceivePort readyPort) {
+    Completer completer = new Completer<Isolate>.sync();
+    readyPort.handler = (readyMessage) {
+      readyPort.close();
+      if (readyMessage is List && readyMessage.length == 2) {
+        SendPort controlPort = readyMessage[0];
+        List capabilities = readyMessage[1];
+        completer.complete(new Isolate(controlPort,
+                                       pauseCapability: capabilities[0],
+                                       terminateCapability: capabilities[1]));
+      } else if (readyMessage is String) {
+        // We encountered an error while starting the new isolate.
+        completer.completeError(new IsolateSpawnException(
+            'Unable to spawn isolate: ${readyMessage}'));
+      } else {
+        // This shouldn't happen.
+        completer.completeError(new IsolateSpawnException(
+            "Internal error: unexpected format for ready message: "
+            "'${readyMessage}'"));
+      }
+    };
     return completer.future;
   }
 
   // TODO(iposva): Cleanup to have only one definition.
   // These values need to be kept in sync with the class IsolateMessageHandler
   // in vm/isolate.cc.
   static const _PAUSE = 1;
   static const _RESUME = 2;
   static const _PING = 3;
   static const _KILL = 4;
@@ skipping 103 matching lines @@
   static Isolate _getCurrentIsolate() {
     List portAndCapabilities = _getPortAndCapabilitiesOfCurrentIsolate();
     return new Isolate(portAndCapabilities[0],
                        pauseCapability: portAndCapabilities[1],
                        terminateCapability: portAndCapabilities[2]);
   }
 
   static List _getPortAndCapabilitiesOfCurrentIsolate()
       native "Isolate_getPortAndCapabilitiesOfCurrentIsolate";
 }