[CachedAccessor] for window.document.

third_party/WebKit/Source/bindings/core/v8/WindowProxy.cpp

 /*
  * Copyright (C) 2008, 2009, 2011 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 24 matching lines @@
 #include "bindings/core/v8/V8Binding.h"
 #include "bindings/core/v8/V8DOMActivityLogger.h"
 #include "bindings/core/v8/V8Document.h"
 #include "bindings/core/v8/V8GCForContextDispose.h"
 #include "bindings/core/v8/V8HTMLCollection.h"
 #include "bindings/core/v8/V8HTMLDocument.h"
 #include "bindings/core/v8/V8HiddenValue.h"
 #include "bindings/core/v8/V8Initializer.h"
 #include "bindings/core/v8/V8ObjectConstructor.h"
 #include "bindings/core/v8/V8PagePopupControllerBinding.h"
+#include "bindings/core/v8/V8PrivateProperty.h"
 #include "bindings/core/v8/V8Window.h"
 #include "core/frame/LocalFrame.h"
 #include "core/frame/csp/ContentSecurityPolicy.h"
 #include "core/html/DocumentNameCollection.h"
 #include "core/html/HTMLCollection.h"
 #include "core/html/HTMLIFrameElement.h"
 #include "core/inspector/InspectorInstrumentation.h"
 #include "core/inspector/MainThreadDebugger.h"
 #include "core/loader/DocumentLoader.h"
 #include "core/loader/FrameLoader.h"
@@ skipping 355 matching lines @@
       toV8(frame->document(), context->Global(), context->GetIsolate());
   if (documentWrapper.IsEmpty())
     return;
   ASSERT(documentWrapper == m_document.newLocal(m_isolate) ||
          m_document.isEmpty());
   if (m_document.isEmpty())
     updateDocumentWrapper(v8::Local<v8::Object>::Cast(documentWrapper));
   checkDocumentWrapper(m_document.newLocal(m_isolate), frame->document());
 
   ASSERT(documentWrapper->IsObject());
-  // TODO(jochen): Don't replace the accessor with a data value. We need a way
-  // to tell v8 that the accessor's return value won't change after this point.
-  if (!v8CallBoolean(context->Global()->ForceSet(
-          context, v8AtomicString(m_isolate, "document"), documentWrapper,
-          static_cast<v8::PropertyAttribute>(v8::ReadOnly | v8::DontDelete))))
-    return;
+
+  // Update cached accessor.
+  CHECK(V8PrivateProperty::getWindowDocumentCachedAccessor(m_isolate).set(

[jochen (gone - plz use gerrit), 2016/10/20 08:44:42]

how does this work for isolated worlds? This method (updateDocumentProperty)
bails out for non-main-worlds

[vogelheim, 2016/10/20 13:27:59]

Yes.

main world:
- accessor gets created with hidden, 'cached' accessor
- value gets set here.
- the real & slow accessor still exists. any code paths that don't know about
cached accessors use the real accessor (with a speed penalty)

non-main worlds:
- the first two steps don't happen.
- all accessors use the 'true' accessor.

We could change that, if we think this penalizes non-main-worlds too much. But
that's how it works in this CL.

+      context, context->Global(), documentWrapper));
 }
 
 void WindowProxy::updateActivityLogger() {
   m_scriptState->perContextData()->setActivityLogger(
       V8DOMActivityLogger::activityLogger(
           m_world->worldId(),
           m_frame->isLocalFrame() && toLocalFrame(m_frame)->document()
               ? toLocalFrame(m_frame)->document()->baseURI()
               : KURL()));
 }
@@ skipping 140 matching lines @@
                          v8String(m_isolate, name));
 }
 
 void WindowProxy::updateSecurityOrigin(SecurityOrigin* origin) {
   if (!isContextInitialized())
     return;
   setSecurityToken(origin);
 }
 
 }  // namespace blink