Store end_callback and callback_data into local variables before dropping the monitor

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 adfda8e2fd6c95786c7787fa6c0f5dab389c31f6..936e711684f145dbea421ca7b2e4397934458d69 100644
--- a/runtime/vm/message_handler.cc
+++ b/runtime/vm/message_handler.cc
@@ -332,6 +332,8 @@ void MessageHandler::TaskCallback() {
   MessageStatus status = kOK;
   bool run_end_callback = false;
   bool delete_me = false;
+  EndCallback end_callback = NULL;
+  CallbackData callback_data = NULL;
   {
     // We will occasionally release and reacquire this monitor in this
     // function. Whenever we reacquire the monitor we *must* process
@@ -415,6 +417,8 @@ void MessageHandler::TaskCallback() {
       }
       pool_ = NULL;
       // Decide if we have a callback before releasing the monitor.
+      end_callback = end_callback_;
+      callback_data = callback_data_;
       run_end_callback = end_callback_ != NULL;
       delete_me = delete_me_;
     }
@@ -432,7 +436,8 @@ void MessageHandler::TaskCallback() {
   ASSERT(!delete_me || !run_end_callback);
 
   if (run_end_callback) {

[siva, 2017/01/24 19:24:25]

is run_end_callback still needed, it could just be replaced everywhere
with (end_callback != NULL)

-    end_callback_(callback_data_);
+    ASSERT(end_callback != NULL);
+    end_callback(callback_data);
     // The handler may have been deleted after this point.
   }
   if (delete_me) {