Revert my last change. Odd test failures that I will investigate tomorrow.

runtime/vm/message.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/message.h"
 
 namespace dart {
 
 DECLARE_FLAG(bool, trace_isolates);
 
@@ skipping 36 matching lines @@
     }
     OS::Print("[>] Posting message:\n"
               "\tsource:     %s\n"
               "\treply_port: %lld\n"
               "\tdest:       %s\n"
               "\tdest_port:  %lld\n",
               source_name, message->reply_port(), name(), message->dest_port());
   }
 
   Message::Priority priority = message->priority();
-  {
-    MonitorLocker ml(&monitor_);
-    queue_->Enqueue(message);
-    monitor_.Notify();
-    message = NULL;  // Do not access message.  May have been deleted.
-  }
+  queue()->Enqueue(message);
+  message = NULL;  // Do not access message.  May have been deleted.
 
   // Invoke any custom message notification.
   MessageNotify(priority);
 }
 
 
-Message* MessageHandler::DequeueNoWait() {
-  MonitorLocker ml(&monitor_);
-  return queue_->Dequeue();
-}
-
-
-Message* MessageHandler::Dequeue(int64_t millis) {
-  ASSERT(millis >= 0);
-  MonitorLocker ml(&monitor_);
-  Message* result = queue_->Dequeue();
-  if (result == NULL) {
-    // No message available at any priority.
-    monitor_.Wait(millis);
-    result = queue_->Dequeue();
-  }
-  return result;
-}
-
-
 void MessageHandler::ClosePort(Dart_Port port) {
-  MonitorLocker ml(&monitor_);
-  queue_->Flush(port);
+  queue()->Flush(port);
 }
 
 
 void MessageHandler::CloseAllPorts() {
-  MonitorLocker ml(&monitor_);
-  queue_->FlushAll();
+  queue()->FlushAll();
 }
 
 
 MessageQueue::MessageQueue() {
   for (int p = Message::kFirstPriority; p < Message::kNumPriorities; p++) {
     head_[p] = NULL;
     tail_[p] = NULL;
   }
 }
 
 
 MessageQueue::~MessageQueue() {
   // Ensure that all pending messages have been released.
 #if defined(DEBUG)
   for (int p = Message::kFirstPriority; p < Message::kNumPriorities; p++) {
     ASSERT(head_[p] == NULL);
   }
 #endif
 }
 
 
 void MessageQueue::Enqueue(Message* msg) {
+  MonitorLocker ml(&monitor_);
   Message::Priority p = msg->priority();
   // Make sure messages are not reused.
   ASSERT(msg->next_ == NULL);
   if (head_[p] == NULL) {
     // Only element in the queue.
     head_[p] = msg;
     tail_[p] = msg;
+
+    // We only need to notify if the queue was empty.
+    monitor_.Notify();
   } else {
     ASSERT(tail_[p] != NULL);
     // Append at the tail.
     tail_[p]->next_ = msg;
     tail_[p] = msg;
   }
 }
 
+Message* MessageQueue::DequeueNoWait() {
+  MonitorLocker ml(&monitor_);
+  return DequeueNoWaitHoldsLock();
+}
 
-Message* MessageQueue::Dequeue() {
+Message* MessageQueue::DequeueNoWaitHoldsLock() {
   // Look for the highest priority available message.
   for (int p = Message::kNumPriorities-1; p >= Message::kFirstPriority; p--) {
     Message* result = head_[p];
     if (result != NULL) {
       head_[p] = result->next_;
       // The following update to tail_ is not strictly needed.
       if (head_[p] == NULL) {
         tail_[p] = NULL;
       }
 #if defined(DEBUG)
       result->next_ = result;  // Make sure to trigger ASSERT in Enqueue.
 #endif  // DEBUG
       return result;
     }
   }
   return NULL;
 }
 
 
+Message* MessageQueue::Dequeue(int64_t millis) {
+  ASSERT(millis >= 0);
+  MonitorLocker ml(&monitor_);
+  Message* result = DequeueNoWaitHoldsLock();
+  if (result == NULL) {
+    // No message available at any priority.
+    monitor_.Wait(millis);
+    result = DequeueNoWaitHoldsLock();
+  }
+  return result;
+}
+
+
 void MessageQueue::Flush(Dart_Port port) {
+  MonitorLocker ml(&monitor_);
   for (int p = Message::kFirstPriority; p < Message::kNumPriorities; p++) {
     Message* cur = head_[p];
     Message* prev = NULL;
     while (cur != NULL) {
       Message* next = cur->next_;
       // If the message matches, then remove it from the queue and delete it.
       if (cur->dest_port() == port) {
         if (prev != NULL) {
           prev->next_ = next;
         } else {
           head_[p] = next;
         }
         delete cur;
       } else {
         // Move prev forward.
         prev = cur;
       }
       // Advance to the next message in the queue.
       cur = next;
     }
     tail_[p] = prev;
   }
 }
 
 
 void MessageQueue::FlushAll() {
+  MonitorLocker ml(&monitor_);
   for (int p = Message::kFirstPriority; p < Message::kNumPriorities; p++) {
     Message* cur = head_[p];
     head_[p] = NULL;
     tail_[p] = NULL;
     while (cur != NULL) {
       Message* next = cur->next_;
       delete cur;
       cur = next;
     }
   }
 }
 
 
 }  // namespace dart