[wrapper-tracing] Emite write barrier upon associating a wrapper

third_party/WebKit/Source/bindings/core/v8/ScriptWrappable.h

 /*
  * Copyright (C) 2010 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 13 matching lines @@
  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef ScriptWrappable_h
 #define ScriptWrappable_h
 
+#include "bindings/core/v8/ScriptWrappableVisitor.h"
 #include "bindings/core/v8/WrapperTypeInfo.h"
 #include "core/CoreExport.h"
 #include "platform/heap/Handle.h"
 #include "v8/include/v8.h"
 #include "wtf/Compiler.h"
 #include "wtf/Noncopyable.h"
 #include "wtf/TypeTraits.h"
 
 namespace blink {
 
@@ skipping 74 matching lines @@
                                      v8::Local<v8::Object>& wrapper) {
     ASSERT(!wrapper.IsEmpty());
     if (UNLIKELY(containsWrapper())) {
       wrapper = mainWorldWrapper(isolate);
       return false;
     }
     m_mainWorldWrapper.Reset(isolate, wrapper);
     wrapperTypeInfo->configureWrapper(&m_mainWorldWrapper);
     m_mainWorldWrapper.SetWeak();
     ASSERT(containsWrapper());
+    ScriptWrappableVisitor::writeBarrier(this, &m_mainWorldWrapper);

[jochen (gone - plz use gerrit), 2017/03/20 20:59:39]

"this" is not necessarily pointing to the beginning of the object...

[Michael Lippautz, 2017/03/20 21:04:22]

do you have an example? I think it was the assumption that SW always has 'this'
pointing to the object start. as far as I can see we only have GarbageCollected
and GarbageCollectedFinalized in front of SW in the inheritance hierarchy. 

     return true;
   }
 
   bool isEqualTo(const v8::Local<v8::Object>& other) const {
     return m_mainWorldWrapper == other;
   }
 
   // Provides a way to convert Node* to ScriptWrappable* without including
   // "core/dom/Node.h".
   //
@@ skipping 73 matching lines @@
 #define DECLARE_WRAPPERTYPEINFO()                          \
  public:                                                   \
   const WrapperTypeInfo* wrapperTypeInfo() const override; \
                                                            \
  private:                                                  \
   typedef void end_of_define_wrappertypeinfo_not_reached_t
 
 }  // namespace blink
 
 #endif  // ScriptWrappable_h