binding: Reimplements V8HiddenValue as V8PrivateProperty.

third_party/WebKit/Source/bindings/core/v8/V8PrivateProperty.h

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef V8PrivateProperty_h
+#define V8PrivateProperty_h
+
+#include "bindings/core/v8/ScopedPersistent.h"
+#include "bindings/core/v8/ScriptPromiseProperties.h"
+#include "bindings/core/v8/V8BindingMacros.h"
+#include "bindings/core/v8/V8PerIsolateData.h"
+#include "core/CoreExport.h"
+#include "wtf/Allocator.h"
+#include <memory>
+#include <v8.h>
+
+namespace blink {
+
+class ScriptState;
+class ScriptWrappable;
+
+// Apply |X| for each pair of (InterfaceName, PrivateKeyName).
+#define V8_PRIVATE_PROPERTY_FOR_EACH(X) \
+    X(MessageEvent, CachedData)
+
+// The getter's name for a private property.
+#define V8_PRIVATE_PROPERTY_GETTER_NAME(InterfaceName, PrivateKeyName) \
+    get##InterfaceName##PrivateKeyName
+
+// The member variable's name for a private property.
+#define V8_PRIVATE_PROPERTY_MEMBER_NAME(InterfaceName, PrivateKeyName) \
+    m_symbol##InterfaceName##PrivateKeyName
+
+// The string used to create a private symbol.  Must be unique per V8 instance.
+#define V8_PRIVATE_PROPERTY_SYMBOL_STRING(InterfaceName, PrivateKeyName) \
+    #InterfaceName"#"#PrivateKeyName // NOLINT(whitespace/indent)
+
+// Provides access to V8's private properties.
+//
+// Usage 1) Fast path to use a pre-registered symbol.
+//   auto private = V8PrivateProperty::getMessageEventCachedData(isolate);
+//   v8::Local<v8::Context> context = ...;
+//   v8::Local<v8::Object> object = ...;
+//   v8::Local<v8::Value> value = private.get(context, object);
+//   value = ...;
+//   private.set(context, object, value);
+//
+// Usage 2) Slow path to create a global private symbol.
+//   const char symbolName[] = "Interface#PrivateKeyName";
+//   auto private = V8PrivateProperty::createSymbol(isolate, symbolName, sizeof symbolName);
+//   ...
+class CORE_EXPORT V8PrivateProperty {
+    USING_FAST_MALLOC(V8PrivateProperty);
+    WTF_MAKE_NONCOPYABLE(V8PrivateProperty);
+public:
+    // Provides fast access to V8's private properties.
+    //
+    // Retrieving/creating a global private symbol from a string is very
+    // expensive compared to get or set a private property.  This class
+    // provides a way to cache a private symbol and re-use it.
+    class CORE_EXPORT Symbol {
+        STACK_ALLOCATED();
+    public:
+        v8::Local<v8::Value> get(v8::Local<v8::Context> context, v8::Local<v8::Object> object)
+        {
+            v8::Local<v8::Value> value;
+            if (object->GetPrivate(context, m_privateSymbol).ToLocal(&value))
+                return value;
+            return v8::Local<v8::Value>();
+        }
+        v8::Local<v8::Value> get(v8::Local<v8::Object> object)
+        {
+            return get(m_isolate->GetCurrentContext(), object);
+        }
+
+        bool set(v8::Local<v8::Context> context, v8::Local<v8::Object> object, v8::Local<v8::Value> value)
+        {
+            return v8CallBoolean(object->SetPrivate(context, m_privateSymbol, value));
+        }
+        bool set(v8::Local<v8::Object> object, v8::Local<v8::Value> value)
+        {
+            return set(m_isolate->GetCurrentContext(), object, value);
+        }
+
+        v8::Local<v8::Value> getFromMainWorld(ScriptState*, ScriptWrappable*);

[haraken, 2016/05/24 17:33:53]

Add a comment that this method should not be used unless you understand what
you're doing. It's dangerous to return a main world's wrapper to another world.

[Yuki, 2016/05/26 10:52:11]

Made this one a private: member.

+
+    private:
+        friend class V8PrivateProperty;
+
+        Symbol(v8::Isolate* isolate, v8::Local<v8::Private> privateSymbol)
+            : m_isolate(isolate)
+            , m_privateSymbol(privateSymbol) { }
+
+        v8::Isolate* m_isolate;

[haraken, 2016/05/24 17:33:53]

Instead of caching m_isolate, can we cache v8::Context (because Symbol should be
associated with v8::Context)? Then you don't need to call
m_isolate->GetCurrentContext() in get().

[Yuki, 2016/05/26 10:52:11]

v8::Private itself is NOT associated with any v8::Context.  v8::Context is
needed when we access to a v8::Object which may hold a private property.

Considering isolate->GetCurrentContext() is not that cheap, I'd like to avoid to
call it as much as possible.

Note that we support two overloaded versions of |get|, and the first version
that takes |context| is recommended.
    value = private.get(context, object);
where |context| is the context you already have.  For example,
    value = private.get(scriptState->context(), object);
is more efficient than isolate->GetCurrentContext().

+        v8::Local<v8::Private> m_privateSymbol;
+    };
+
+    static std::unique_ptr<V8PrivateProperty> create()
+    {
+        return std::unique_ptr<V8PrivateProperty>(new V8PrivateProperty());

[haraken, 2016/05/24 17:33:53]

base::wrapUnique ?

[Yuki, 2016/05/26 10:52:11]

Done.

+    }
+
+#define V8_PRIVATE_PROPERTY_DEFINE_GETTER(InterfaceName, KeyName) \
+    static Symbol V8_PRIVATE_PROPERTY_GETTER_NAME(InterfaceName, KeyName)(v8::Isolate* isolate) /* NOLINT(readability/naming/underscores) */ \
+    { \
+        V8PrivateProperty* privateProp = V8PerIsolateData::from(isolate)->privateProperty(); \
+        if (privateProp->V8_PRIVATE_PROPERTY_MEMBER_NAME(InterfaceName, KeyName).isEmpty()) { \

[haraken, 2016/05/24 17:33:53]

Add UNLIKELY?

[Yuki, 2016/05/26 10:52:11]

Done.

+            privateProp->V8_PRIVATE_PROPERTY_MEMBER_NAME(InterfaceName, KeyName).set( \
+                isolate, \
+                createV8Private( \
+                    isolate, \
+                    V8_PRIVATE_PROPERTY_SYMBOL_STRING(InterfaceName, KeyName), \
+                    sizeof V8_PRIVATE_PROPERTY_SYMBOL_STRING(InterfaceName, KeyName))); /* NOLINT(readability/naming/underscores) */ \
+        } \
+        return Symbol(isolate, privateProp->V8_PRIVATE_PROPERTY_MEMBER_NAME(InterfaceName, KeyName).newLocal(isolate)); \
+    }
+    V8_PRIVATE_PROPERTY_FOR_EACH(V8_PRIVATE_PROPERTY_DEFINE_GETTER)
+#undef V8_PRIVATE_PROPERTY_DEFINE_GETTER
+
+    static Symbol createSymbol(v8::Isolate* isolate, const char* symbol, size_t length)
+    {
+        return Symbol(isolate, createV8Private(isolate, symbol, length));
+    }
+
+private:
+    V8PrivateProperty() { }
+
+    static v8::Local<v8::Private> createV8Private(v8::Isolate*, const char* symbol, size_t length);
+
+#define V8_PRIVATE_PROPERTY_DECLARE_MEMBER(InterfaceName, KeyName) \
+    ScopedPersistent<v8::Private> V8_PRIVATE_PROPERTY_MEMBER_NAME(InterfaceName, KeyName); // NOLINT(readability/naming/underscores)
+    V8_PRIVATE_PROPERTY_FOR_EACH(V8_PRIVATE_PROPERTY_DECLARE_MEMBER)
+#undef V8_PRIVATE_PROPERTY_DECLARE_MEMBER
+};
+
+} // namespace blink
+
+#endif // V8PrivateProperty_h