Fix more races in MessageQueue_WaitNotify. My notifies could show up

runtime/vm/message_queue_test.cc

 // Copyright (c) 2011, 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 "vm/assert.h"
 #include "vm/message_queue.h"
 #include "vm/unit_test.h"
 
 namespace dart {
 
@@ skipping 45 matching lines @@
 // A thread which receives an expected sequence of messages.
 static Monitor* sync = NULL;
 static MessageQueue* shared_queue = NULL;
 void MessageReceiver_start(uword unused) {
   // We only need an isolate here because the MonitorLocker in the
   // MessageQueue expects it.
   Dart::CreateIsolate(NULL, NULL);
 
   // 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++) {
     PortMessage* msg = queue->Dequeue(0);
     EXPECT(msg != NULL);
     EXPECT_EQ(i+10, msg->dest_port());
     EXPECT_EQ(i+100, msg->reply_port());
     EXPECT_EQ(i+1000, *(reinterpret_cast<int*>(msg->data())));
     delete msg;
   }
   for (int i = 0; i < 3; i++) {
@@ skipping 10 matching lines @@
 }
 
 
 TEST_CASE(MessageQueue_WaitNotify) {
   sync = new Monitor();
 
   Thread* thread = new Thread(MessageReceiver_start, 0);
   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);
 
   // Pile up three messages before the other thread runs.
   for (int i = 0; i < 3; i++) {
     int* data = reinterpret_cast<int*>(malloc(sizeof(*data)));
     *data = i+1000;
     PortMessage* msg = new PortMessage(i+10, i+100, data);
     shared_queue->Enqueue(msg);
   }
 
@@ skipping 95 matching lines @@
 
   EXPECT(!queue_peer.HasMessage());
   queue.Flush(port1);
 
   // Queue is still empty.
   EXPECT(!queue_peer.HasMessage());
 }
 
 
 }  // namespace dart