InstanceCounter/Oilpan GC tracing: Add clang support

Source/platform/heap/Heap.cpp

 /*
  * Copyright (C) 2013 Google Inc. 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
@@ skipping 1296 matching lines @@
 #endif
 
     inline void visitHeader(HeapObjectHeader* header, const void* objectPointer, TraceCallback callback)
     {
         ASSERT(header);
         ASSERT(objectPointer);
         if (header->isMarked())
             return;
         header->mark();
 #if ENABLE(GC_TRACING)
+        MutexLocker locker(objectGraphMutex());
         String className(classOf(objectPointer));
         {
             LiveObjectMap::AddResult result = currentlyLive().add(className, LiveObjectSet());
             result.storedValue->value.add(reinterpret_cast<uintptr_t>(objectPointer));
         }
         ObjectGraph::AddResult result = objectGraph().add(reinterpret_cast<uintptr_t>(objectPointer), std::make_pair(reinterpret_cast<uintptr_t>(m_hostObject), m_hostName));
         ASSERT(result.isNewEntry);
         // printf("%s[%p] -> %s[%p]\n", m_hostName.ascii().data(), m_hostObject, className.ascii().data(), objectPointer);
 #endif
         if (callback)
@@ skipping 135 matching lines @@
             it = graph.find(it->value.first);
         }
         printf("\n");
     }
 
     static void dumpPathToObjectOnNextGC(void* p)
     {
         objectsToFindPath().add(reinterpret_cast<uintptr_t>(p));
     }
 
+    static Mutex& objectGraphMutex()
+    {
+        AtomicallyInitializedStatic(Mutex&, mutex = *new Mutex);

[tkent, 2014/05/29 12:43:05]

This looks unnatural.
Does the following work?
    AtomicallyInitializedStatic(Mutex, mutex);

+        return mutex;
+    }
+
     static LiveObjectMap& previouslyLive()
     {
         DEFINE_STATIC_LOCAL(LiveObjectMap, map, ());
         return map;
     }
 
     static LiveObjectMap& currentlyLive()
     {
         DEFINE_STATIC_LOCAL(LiveObjectMap, map, ());
         return map;
@@ skipping 272 matching lines @@
 template class ThreadHeap<FinalizedHeapObjectHeader>;
 template class ThreadHeap<HeapObjectHeader>;
 
 Visitor* Heap::s_markingVisitor;
 CallbackStack* Heap::s_markingStack;
 CallbackStack* Heap::s_weakCallbackStack;
 HeapDoesNotContainCache* Heap::s_heapDoesNotContainCache;
 bool Heap::s_shutdownCalled = false;
 bool Heap::s_lastGCWasConservative = false;
 }