Enables clean VM shutdown.

runtime/vm/message_handler.cc

Index: runtime/vm/message_handler.cc
diff --git a/runtime/vm/message_handler.cc b/runtime/vm/message_handler.cc
index 6a473dd74033f4c6d019be2437de0c7a8ec29aa9..9dfa730379dc88d9eefbd91c7a323cb3beaf041e 100644
--- a/runtime/vm/message_handler.cc
+++ b/runtime/vm/message_handler.cc
@@ -42,7 +42,7 @@ MessageHandler::MessageHandler()
       pause_on_exit_(false),
       paused_on_start_(false),
       paused_on_exit_(false),
-      pool_(NULL),
+      running_(false),
       task_(NULL),
       start_callback_(NULL),
       end_callback_(NULL),
@@ -75,8 +75,7 @@ void MessageHandler::MessageNotify(Message::Priority priority) {
 }
 
 
-void MessageHandler::Run(ThreadPool* pool,
-                         StartCallback start_callback,
+void MessageHandler::Run(StartCallback start_callback,
                          EndCallback end_callback,
                          CallbackData data) {
   MonitorLocker ml(&monitor_);
@@ -85,13 +84,13 @@ void MessageHandler::Run(ThreadPool* pool,
               "\thandler:    %s\n",
               name());
   }
-  ASSERT(pool_ == NULL);
-  pool_ = pool;
+  ASSERT(!running_);
+  running_ = true;

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

I think that "running_" is a bit confusing as a name.  I would be happier with a
name like "running_on_thread_pool_".   This would distinguish from those message
handlers that run, for example, in dartium's event loop.

[zra, 2015/07/20 22:23:39]

Done.

   start_callback_ = start_callback;
   end_callback_ = end_callback;
   callback_data_ = data;
   task_ = new MessageHandlerTask(this);
-  pool_->Run(task_);
+  ThreadPool::Run(task_);
 }
 
 
@@ -121,9 +120,9 @@ void MessageHandler::PostMessage(Message* message, bool before_events) {
     }
     message = NULL;  // Do not access message.  May have been deleted.
 
-    if (pool_ != NULL && task_ == NULL) {
+    if (running_ && task_ == NULL) {
       task_ = new MessageHandlerTask(this);
-      pool_->Run(task_);
+      ThreadPool::Run(task_);
     }
   }
   // Invoke any custom message notification.
@@ -205,7 +204,7 @@ bool MessageHandler::HandleNextMessage() {
   // We can only call HandleNextMessage when this handler is not
   // assigned to a thread pool.

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

Update comment.

[zra, 2015/07/20 22:23:39]

Done.

   MonitorLocker ml(&monitor_);
-  ASSERT(pool_ == NULL);
+  ASSERT(!running_);
 #if defined(DEBUG)
   CheckAccess();
 #endif
@@ -288,7 +287,7 @@ void MessageHandler::TaskCallback() {
                   (ok ? "no live ports" : "error"),
                   name());
         }
-        pool_ = NULL;
+        running_ = false;
         run_end_callback = true;
         paused_on_exit_ = false;
       }