third_party/WebKit/Source/core/dom/ElementData.h

/*
 * Copyright (C) 2013 Google Inc. All rights reserved.
 * Copyright (C) 2014 Apple 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
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
 *     * Neither the name of Google Inc. nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#ifndef ElementData_h
#define ElementData_h

#include "build/build_config.h"
#include "core/dom/Attribute.h"
#include "core/dom/AttributeCollection.h"
#include "core/dom/SpaceSplitString.h"
#include "platform/heap/Handle.h"
#include "platform/wtf/text/AtomicString.h"

namespace blink {

class ShareableElementData;
class CSSPropertyValueSet;
class UniqueElementData;

// ElementData represents very common, but not necessarily unique to an element,
// data such as attributes, inline style, and parsed class names and ids.
class ElementData : public GarbageCollectedFinalized<ElementData> {
 public:
  // Override GarbageCollectedFinalized's finalizeGarbageCollectedObject to
  // dispatch to the correct subclass destructor.
  void FinalizeGarbageCollectedObject();

  void ClearClass() const { class_names_.Clear(); }
  void SetClass(const AtomicString& class_name, bool should_fold_case) const {
    class_names_.Set(should_fold_case ? class_name.LowerASCII() : class_name);
  }
  const SpaceSplitString& ClassNames() const { return class_names_; }

  const AtomicString& IdForStyleResolution() const {
    return id_for_style_resolution_;
  }
  void SetIdForStyleResolution(const AtomicString& new_id) const {
    id_for_style_resolution_ = new_id;
  }

  const CSSPropertyValueSet* InlineStyle() const { return inline_style_.Get(); }

  const CSSPropertyValueSet* PresentationAttributeStyle() const;

  AttributeCollection Attributes() const;

  bool HasID() const { return !id_for_style_resolution_.IsNull(); }
  bool HasClass() const { return !class_names_.IsNull(); }

  bool IsEquivalent(const ElementData* other) const;

  bool IsUnique() const { return is_unique_; }

  void TraceAfterDispatch(blink::Visitor*);
  void Trace(blink::Visitor*);

 protected:
  ElementData();
  explicit ElementData(unsigned array_size);
  ElementData(const ElementData&, bool is_unique);

  // Keep the type in a bitfield instead of using virtual destructors to avoid
  // adding a vtable.
  unsigned is_unique_ : 1;
  unsigned array_size_ : 28;
  mutable unsigned presentation_attribute_style_is_dirty_ : 1;
  mutable unsigned style_attribute_is_dirty_ : 1;
  mutable unsigned animated_svg_attributes_are_dirty_ : 1;

  mutable Member<CSSPropertyValueSet> inline_style_;
  mutable SpaceSplitString class_names_;
  mutable AtomicString id_for_style_resolution_;

 private:
  friend class Element;
  friend class ShareableElementData;
  friend class UniqueElementData;
  friend class SVGElement;

  UniqueElementData* MakeUniqueCopy() const;
};

#define DEFINE_ELEMENT_DATA_TYPE_CASTS(thisType, pointerPredicate, \
                                       referencePredicate)         \
  DEFINE_TYPE_CASTS(thisType, ElementData, data, pointerPredicate, \
                    referencePredicate)

#if defined(COMPILER_MSVC)
#pragma warning(push)
// Disable "zero-sized array in struct/union" warning
#pragma warning(disable : 4200)
#endif

// SharableElementData is managed by ElementDataCache and is produced by
// the parser during page load for elements that have identical attributes. This
// is a memory optimization since it's very common for many elements to have
// duplicate sets of attributes (ex. the same classes).
class ShareableElementData final : public ElementData {
 public:
  static ShareableElementData* CreateWithAttributes(const Vector<Attribute>&);

  explicit ShareableElementData(const Vector<Attribute>&);
  explicit ShareableElementData(const UniqueElementData&);
  ~ShareableElementData();

  void TraceAfterDispatch(blink::Visitor* visitor) {
    ElementData::TraceAfterDispatch(visitor);
  }

  // Add support for placement new as ShareableElementData is not allocated
  // with a fixed size. Instead the allocated memory size is computed based on
  // the number of attributes. This requires us to use ThreadHeap::allocate
  // directly with the computed size and subsequently call placement new with
  // the allocated memory address.
  void* operator new(std::size_t, void* location) { return location; }

  AttributeCollection Attributes() const;

  Attribute attribute_array_[0];
};

DEFINE_ELEMENT_DATA_TYPE_CASTS(ShareableElementData,
                               !data->IsUnique(),
                               !data.IsUnique());

#if defined(COMPILER_MSVC)
#pragma warning(pop)
#endif

// UniqueElementData is created when an element needs to mutate its attributes
// or gains presentation attribute style (ex. width="10"). It does not need to
// be created to fill in values in the ElementData that are derived from
// attributes. For example populating the m_inlineStyle from the style attribute
// doesn't require a UniqueElementData as all elements with the same style
// attribute will have the same inline style.
class UniqueElementData final : public ElementData {
 public:
  static UniqueElementData* Create();
  ShareableElementData* MakeShareableCopy() const;

  MutableAttributeCollection Attributes();
  AttributeCollection Attributes() const;

  UniqueElementData();
  explicit UniqueElementData(const ShareableElementData&);
  explicit UniqueElementData(const UniqueElementData&);

  void TraceAfterDispatch(blink::Visitor*);

  // FIXME: We might want to support sharing element data for elements with
  // presentation attribute style. Lots of table cells likely have the same
  // attributes. Most modern pages don't use presentation attributes though
  // so this might not make sense.
  mutable Member<CSSPropertyValueSet> presentation_attribute_style_;
  AttributeVector attribute_vector_;
};

DEFINE_ELEMENT_DATA_TYPE_CASTS(UniqueElementData,
                               data->IsUnique(),
                               data.IsUnique());

inline const CSSPropertyValueSet* ElementData::PresentationAttributeStyle()
    const {
  if (!is_unique_)
    return nullptr;
  return ToUniqueElementData(this)->presentation_attribute_style_.Get();
}

inline AttributeCollection ElementData::Attributes() const {
  if (IsUnique())
    return ToUniqueElementData(this)->Attributes();
  return ToShareableElementData(this)->Attributes();
}

inline AttributeCollection ShareableElementData::Attributes() const {
  return AttributeCollection(attribute_array_, array_size_);
}

inline AttributeCollection UniqueElementData::Attributes() const {
  return AttributeCollection(attribute_vector_.data(),
                             attribute_vector_.size());
}

inline MutableAttributeCollection UniqueElementData::Attributes() {
  return MutableAttributeCollection(attribute_vector_);
}

}  // namespace blink

#endif  // ElementData_h