Enables clean VM shutdown.

runtime/bin/dbg_message.cc

Index: runtime/bin/dbg_message.cc
diff --git a/runtime/bin/dbg_message.cc b/runtime/bin/dbg_message.cc
index a6358806daca30d265fda87d03c6b66a7fc05656..5e6a42eb49c71ab590e1c7711abe23d2c0b669da 100644
--- a/runtime/bin/dbg_message.cc
+++ b/runtime/bin/dbg_message.cc
@@ -1402,14 +1402,17 @@ void DbgMsgQueueList::ExceptionThrownHandler(Dart_IsolateId isolate_id,
 
 void DbgMsgQueueList::IsolateEventHandler(Dart_IsolateId isolate_id,
                                           Dart_IsolateEvent kind) {
-  DebuggerConnectionHandler::WaitForConnection();
-  Dart_EnterScope();
   if (kind == kCreated) {
+    DebuggerConnectionHandler::WaitForConnection();

[turnidge, 2015/06/30 22:15:46]

What led to the changes in this file?

[zra, 2015/07/20 22:23:38]

The VM Isolate has no receive queue. Isolate::Shutdown tries to send it a
message anyway. Instead of putting a special case there, we just ignore the
message here if there is no receive queue.

A previous CL attempting to implement that policy neglected to also avoid
calling DebuggerConnectionHandler::WaitForConnection(). This change ensures that
if there is no receive queue, we do absolutely nothing.

+    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) {
@@ -1418,9 +1421,11 @@ void DbgMsgQueueList::IsolateEventHandler(Dart_IsolateId isolate_id,
         ASSERT(kind == kShutdown);
         RemoveIsolateMsgQueue(isolate_id);
       }
+      Dart_ExitScope();
     }
+    // If there is no recieve message queue, do not wait for a connection, and

[turnidge, 2015/06/30 22:15:46]

typo: receive

[zra, 2015/07/20 22:23:38]

Done.

+    // ignore the message.
   }
-  Dart_ExitScope();
 }
 
 }  // namespace bin