Allow race-full access of map instance size when sweeping concurrently.

src/objects.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 10206 matching lines @@
 static void GetMinInobjectSlack(Map* map, void* data) {
   int slack = map->unused_property_fields();
   if (*reinterpret_cast<int*>(data) > slack) {
     *reinterpret_cast<int*>(data) = slack;
   }
 }
 
 
 static void ShrinkInstanceSize(Map* map, void* data) {
   int slack = *reinterpret_cast<int*>(data);
-  map->set_inobject_properties(map->inobject_properties() - slack);
-  map->set_unused_property_fields(map->unused_property_fields() - slack);
-  map->set_instance_size(map->instance_size() - slack * kPointerSize);
-
-  // Visitor id might depend on the instance size, recalculate it.
-  map->set_visitor_id(StaticVisitorBase::GetVisitorId(map));
+  map->Shrink(slack);

[Michael Starzinger, 2014/04/08 11:34:22]

nit: Can we call that Map::ShrinkInstanceSize for readability?

 }
 
 
 void SharedFunctionInfo::CompleteInobjectSlackTracking() {
   ASSERT(live_objects_may_exist() && IsInobjectSlackTrackingInProgress());
   Map* map = Map::cast(initial_map());
 
   Heap* heap = map->GetHeap();
   set_initial_map(heap->undefined_value());
   Builtins* builtins = heap->isolate()->builtins();
@@ skipping 6434 matching lines @@
 #define ERROR_MESSAGES_TEXTS(C, T) T,
   static const char* error_messages_[] = {
       ERROR_MESSAGES_LIST(ERROR_MESSAGES_TEXTS)
   };
 #undef ERROR_MESSAGES_TEXTS
   return error_messages_[reason];
 }
 
 
 } }  // namespace v8::internal