Yesterday's deadlock fix was wrong. It could drop notifications.

runtime/vm/message_handler.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_handler.h"
 
 #include "vm/dart.h"
 #include "vm/lockers.h"
 #include "vm/port.h"
 
@@ skipping 76 matching lines @@
   pool_ = pool;
   start_callback_ = start_callback;
   end_callback_ = end_callback;
   callback_data_ = data;
   task_ = new MessageHandlerTask(this);
   pool_->Run(task_);
 }
 
 
 void MessageHandler::PostMessage(Message* message, bool before_events) {
-  MonitorLocker ml(&monitor_);
-  if (FLAG_trace_isolates) {
-    const char* source_name = "<native code>";
-    Isolate* source_isolate = Isolate::Current();
-    if (source_isolate) {
-      source_name = source_isolate->name();
+  Message::Priority saved_priority;
+  {
+    MonitorLocker ml(&monitor_);
+    if (FLAG_trace_isolates) {
+      const char* source_name = "<native code>";
+      Isolate* source_isolate = Isolate::Current();
+      if (source_isolate) {
+        source_name = source_isolate->name();
+      }
+      OS::Print("[>] Posting message:\n"
+                "\tlen:        %" Pd "\n"
+                "\tsource:     %s\n"
+                "\tdest:       %s\n"
+                "\tdest_port:  %" Pd64 "\n",
+                message->len(), source_name, name(), message->dest_port());
     }
-    OS::Print("[>] Posting message:\n"
-              "\tlen:        %" Pd "\n"
-              "\tsource:     %s\n"
-              "\tdest:       %s\n"
-              "\tdest_port:  %" Pd64 "\n",
-              message->len(), source_name, name(), message->dest_port());
+
+    saved_priority = message->priority();
+    if (message->IsOOB()) {
+      oob_queue_->Enqueue(message, before_events);
+    } else {
+      queue_->Enqueue(message, before_events);
+    }
+    message = NULL;  // Do not access message.  May have been deleted.
+
+    if (pool_ != NULL && task_ == NULL) {
+      task_ = new MessageHandlerTask(this);
+      pool_->Run(task_);
+    }
   }
-
-  Message::Priority saved_priority = message->priority();
-  if (message->IsOOB()) {
-    oob_queue_->Enqueue(message, before_events);
-  } else {
-    queue_->Enqueue(message, before_events);
-  }
-  message = NULL;  // Do not access message.  May have been deleted.
-
-  if (pool_ != NULL && task_ == NULL) {
-    task_ = new MessageHandlerTask(this);
-    pool_->Run(task_);
-  }
-
   // Invoke any custom message notification.
   MessageNotify(saved_priority);
 }
 
 
 Message* MessageHandler::DequeueMessage(Message::Priority min_priority) {
   // TODO(turnidge): Add assert that monitor_ is held here.
   Message* message = oob_queue_->Dequeue();
   if ((message == NULL) && (min_priority < Message::kOOBPriority)) {
     message = queue_->Dequeue();
@@ skipping 190 matching lines @@
 
 void MessageHandler::decrement_live_ports() {
   MonitorLocker ml(&monitor_);
 #if defined(DEBUG)
   CheckAccess();
 #endif
   live_ports_--;
 }
 
 }  // namespace dart