Fix more races in MessageQueue_WaitNotify. My notifies could show up

runtime/vm/message_queue_test.cc

Index: runtime/vm/message_queue_test.cc
===================================================================
--- runtime/vm/message_queue_test.cc	(revision 534)
+++ runtime/vm/message_queue_test.cc	(working copy)
@@ -63,18 +63,19 @@
 
   // Create a message queue and share it.
   MessageQueue* queue = new MessageQueue();
+  MessageQueueTestPeer peer(queue);
   shared_queue = queue;
 
-  // Tell the other thread to fill the queue a bit.
+  // Tell the other thread that the shared queue is ready.
   {
     MonitorLocker ml(sync);
     ml.Notify();
   }

[siva, 2011/10/18 22:19:59]

The update to shared_queue could be under a lock:
{
  MonitorLocker ml(sync);
  shared_queue = queue;
  ml.notify();
}

 
   // Wait for the other thread to fill the queue a bit.
-  {
+  while (!peer.HasMessage()) {
     MonitorLocker ml(sync);
-    ml.Wait(0);
+    ml.Wait(5);
   }

[siva, 2011/10/18 22:19:59]

The check for peer.HasMessage() could be under a lock,
Also we should probably be using a different monitor for
this as the notify could get eaten by the same thread that
did the notify.

{
  MonitorLocker ml(sync1);
  while (!peer.HasMessage()) {
    ml.Wait();
  }
}

 
   for (int i = 0; i < 3; i++) {
@@ -106,9 +107,9 @@
   EXPECT(thread != NULL);
 
   // Wait for the shared queue to be created.
-  {
+  while (shared_queue == NULL) {
     MonitorLocker ml(sync);
-    ml.Wait(0);
+    ml.Wait(5);
   }

[siva, 2011/10/18 22:19:59]

The check for shared queue could be under a lock:
{
  MonitorLocker ml(sync);
  while (shared_queue == NULL) {
    ml.Wait();
  }
}

   ASSERT(shared_queue != NULL);