Clean VM thread shutdown:

runtime/bin/dbg_message.cc

 // 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.
 
 #include "bin/dbg_connection.h"
 #include "bin/dbg_message.h"
 #include "bin/dartutils.h"
 #include "bin/lockers.h"
 #include "bin/thread.h"
 #include "bin/utils.h"
@@ skipping 1384 matching lines @@
   ASSERT(msg_queue != NULL);
   msg_queue->SendQueuedMsgs();
   msg_queue->SendExceptionEvent(exception, stack_trace);
   msg_queue->MessageLoop();
   Dart_ExitScope();
 }
 
 
 void DbgMsgQueueList::IsolateEventHandler(Dart_IsolateId isolate_id,
                                           Dart_IsolateEvent kind) {
-  DebuggerConnectionHandler::WaitForConnection();
-  Dart_EnterScope();
   if (kind == kCreated) {
+    DebuggerConnectionHandler::WaitForConnection();
+    Dart_EnterScope();
     DbgMsgQueue* msg_queue = AddIsolateMsgQueue(isolate_id);
     msg_queue->SendIsolateEvent(isolate_id, kind);
+    Dart_ExitScope();
   } else {
     DbgMsgQueue* msg_queue = GetIsolateMsgQueue(isolate_id);
     if (msg_queue != NULL) {
+      DebuggerConnectionHandler::WaitForConnection();
+      Dart_EnterScope();
       msg_queue->SendQueuedMsgs();
       msg_queue->SendIsolateEvent(isolate_id, kind);
       if (kind == kInterrupted) {
         msg_queue->MessageLoop();
       } else {
         ASSERT(kind == kShutdown);
         RemoveIsolateMsgQueue(isolate_id);
       }
+      Dart_ExitScope();
     }
+    // If there is no receive message queue, do not wait for a connection, and
+    // ignore the message.
   }
-  Dart_ExitScope();
 }
 
 }  // namespace bin
 }  // namespace dart