Attempt to fix loader hangs

runtime/bin/vmservice/loader.dart

 // Copyright (c) 2015, 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.
 
 part of vmservice_io;
 
 _sanitizeWindowsPath(path) {
   // For Windows we need to massage the paths a bit according to
   // http://blogs.msdn.com/b/ie/archive/2006/12/06/file-uris-in-windows.aspx
   //
@@ skipping 51 matching lines @@
   FileRequest(this.sp, this.tag, this.uri, this.resolvedUri, this.libraryUrl);
 }
 
 bool _traceLoading = false;
 
 // State associated with the isolate that is used for loading.
 class IsolateLoaderState extends IsolateEmbedderData {
   IsolateLoaderState(this.isolateId);
 
   final int isolateId;
-
+  bool _dead = false;
   SendPort sp;
 
   void init(String packageRootFlag, String packagesConfigFlag,
       String workingDirectory, String rootScript) {
+    if (_dead) {
+      return;
+    }
     // _workingDirectory must be set first.
     _workingDirectory = new Uri.directory(workingDirectory);
     if (rootScript != null) {
       _rootScript = Uri.parse(rootScript);
     }
     // If the --package-root flag was passed.
     if (packageRootFlag != null) {
       _setPackageRoot(packageRootFlag);
     }
     // If the --packages flag was passed.
     if (packagesConfigFlag != null) {
       _setPackagesConfig(packagesConfigFlag);
     }
-    _fileRequestQueue = new List<FileRequest>();
+    if (_fileRequestQueue != null) {
+      _fileRequestQueue = new List<FileRequest>();
+    }
   }
 
   void cleanup() {
+    _dead = true;
     if (_packagesPort != null) {
       _packagesPort.close();
       _packagesPort = null;
     }
   }
 
   // The working directory when the embedder started.
   Uri _workingDirectory;
 
   // The root script's uri.
@@ skipping 144 matching lines @@
     }
     if (_traceLoading) {
       _log("Resolved '$uri' to '$resolvedUri'.");
     }
     return resolvedUri;
   }
 
   RawReceivePort _packagesPort;
 
   void _requestPackagesMap([Uri packageConfig]) {
-    assert(_packagesPort == null);
     assert(_rootScript != null);
+    if (_packagesPort != null) {
+      // Already scheduled.
+      return;
+    }
     // Create a port to receive the packages map on.
     _packagesPort = new RawReceivePort(_handlePackagesReply);
     var sp = _packagesPort.sendPort;
 
     if (packageConfig != null) {
       // Explicitly specified .packages path.
       _handlePackagesRequest(sp, _traceLoading, -2, packageConfig);
     } else {
       // Search for .packages or packages/ starting at the root script.
       _handlePackagesRequest(sp, _traceLoading, -1, _rootScript);
     }
 
     if (_traceLoading) {
       _log("Requested packages map for '$_rootScript'.");
     }
   }
 
   void _handlePackagesReply(msg) {
-    assert(_packagesPort != null);
+    if (_packagesPort == null) {
+      return;
+    }
     // Make sure to close the _packagePort before any other action.
     _packagesPort.close();
     _packagesPort = null;
 
     if (_traceLoading) {
       _log("Got packages reply: $msg");
     }
     if (msg is String) {
       if (_traceLoading) {
         _log("Got failure response on package port: '$msg'");
@@ skipping 850 matching lines @@
         msg[2] = resolvedUri.toString();
         msg[3] = null;
         msg[4] = e.toString();
         sp.send(msg);
       }
       break;
     default:
       _log('Unknown loader request tag=$tag from $isolateId');
   }
 }