Oilpan: DOM wrappers don't need to keep persistent handles

Source/bindings/core/v8/V8GCController.cpp

 /*
  * Copyright (C) 2009 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 438 matching lines @@
 
     static size_t lastUsageReportedToV8 = 0;
 
     size_t currentUsage = Partitions::currentDOMMemoryUsage();
     int64_t diff = static_cast<int64_t>(currentUsage) - static_cast<int64_t>(lastUsageReportedToV8);
     isolate->AdjustAmountOfExternalAllocatedMemory(diff);
 
     lastUsageReportedToV8 = currentUsage;
 }
 
+class DOMWrapperTracer : public v8::PersistentHandleVisitor {
+public:
+    explicit DOMWrapperTracer(Visitor* visitor)
+        : m_visitor(visitor)
+    {
+    }
+
+    virtual void VisitPersistentHandle(v8::Persistent<v8::Value>* value, uint16_t classId) override
+    {
+        if (classId != WrapperTypeInfo::NodeClassId && classId != WrapperTypeInfo::ObjectClassId)
+            return;
+
+        // Casting to a Handle is safe here, since the Persistent doesn't get GCd
+        // during tracing.
+        ASSERT((*reinterpret_cast<v8::Handle<v8::Value>*>(value))->IsObject());
+        v8::Handle<v8::Object>* wrapper = reinterpret_cast<v8::Handle<v8::Object>*>(value);
+        ASSERT(V8DOMWrapper::isDOMWrapper(*wrapper));
+        toWrapperTypeInfo(*wrapper)->trace(m_visitor, toScriptWrappableBase(*wrapper));
+    }
+
+private:
+    Visitor* m_visitor;
+};
+
+void V8GCController::traceDOMWrappers(Visitor* visitor)
+{
+    DOMWrapperTracer tracer(visitor);
+    v8::V8::VisitHandlesWithClassIds(&tracer);

[haraken, 2014/10/15 10:43:04]

This is problematic... When doing an Oilpan's GC, a GCing thread invokes
traceDOMWrappers for each ThreadState. Each traceDOMWrappers is expected to
visit DOM wrappers of each thread, but it doesn't happen because
VisitHandlesWithClassIds visits DOM wrappers of the current isolate (i.e., the
current thread).

As a result, V8GCController::traceDOMWrappers just visits DOM wrappers in the
GCing thread and doesn't trace DOM wrappers in other threads.

+}
+
 } // namespace blink