third_party/blink/renderer/core/dom/presentation_attribute_style.cc

/*
 * Copyright (C) 2013 Google Inc. All rights reserved.
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 * 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.
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 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
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 * 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
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 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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#include "third_party/blink/renderer/core/dom/presentation_attribute_style.h"

#include <algorithm>

#include "third_party/blink/renderer/core/css/css_property_value_set.h"
#include "third_party/blink/renderer/core/dom/attribute.h"
#include "third_party/blink/renderer/core/dom/element.h"
#include "third_party/blink/renderer/core/html/forms/html_input_element.h"
#include "third_party/blink/renderer/platform/heap/garbage_collected.h"
#include "third_party/blink/renderer/platform/wtf/hash_functions.h"
#include "third_party/blink/renderer/platform/wtf/hash_map.h"

namespace blink {

struct PresentationAttributeCacheKey {
  PresentationAttributeCacheKey() : tag_name(nullptr) {}
  StringImpl* tag_name;
  Vector<std::pair<StringImpl*, AtomicString>, 3> attributes_and_values;
};

static bool operator!=(const PresentationAttributeCacheKey& a,
                       const PresentationAttributeCacheKey& b) {
  if (a.tag_name != b.tag_name)
    return true;
  return a.attributes_and_values != b.attributes_and_values;
}

struct PresentationAttributeCacheEntry final
    : public GarbageCollected<PresentationAttributeCacheEntry> {
 public:
  void Trace(Visitor* visitor) const { visitor->Trace(value); }

  PresentationAttributeCacheKey key;
  Member<CSSPropertyValueSet> value;
};

using PresentationAttributeCache =
    HeapHashMap<unsigned,
                Member<PresentationAttributeCacheEntry>,
                AlreadyHashedTraits>;
static PresentationAttributeCache& GetPresentationAttributeCache() {
  DEFINE_STATIC_LOCAL(Persistent<PresentationAttributeCache>, cache,
                      (MakeGarbageCollected<PresentationAttributeCache>()));
  return *cache;
}

static bool AttributeNameSort(const std::pair<StringImpl*, AtomicString>& p1,
                              const std::pair<StringImpl*, AtomicString>& p2) {
  // Sort based on the attribute name pointers. It doesn't matter what the order
  // is as long as it is always the same.
  return p1.first < p2.first;
}

static unsigned ComputePresentationAttributeCacheHash(
    const PresentationAttributeCacheKey& key) {
  DCHECK(key.tag_name);
  DCHECK(key.attributes_and_values.size());
  unsigned attribute_hash = StringHasher::HashMemory(
      key.attributes_and_values.data(),
      key.attributes_and_values.size() * sizeof(key.attributes_and_values[0]));
  return WTF::HashInts(key.tag_name->ExistingHash(), attribute_hash);
}

static unsigned MakePresentationAttributeCacheKey(
    Element& element,
    PresentationAttributeCacheKey& result) {
  // FIXME: Enable for SVG.
  if (!element.IsHTMLElement())
    return 0;
  // Interpretation of the size attributes on <input> depends on the type
  // attribute.
  if (IsA<HTMLInputElement>(element))
    return 0;
  if (element.HasExtraStyleForPresentationAttribute())
    return 0;
  AttributeCollection attributes = element.AttributesWithoutUpdate();
  for (const Attribute& attr : attributes) {
    if (!element.IsPresentationAttribute(attr.GetName()))
      continue;
    if (!attr.NamespaceURI().IsNull())
      return 0;
    // FIXME: Background URL may depend on the base URL and can't be shared.
    // Disallow caching.
    if (attr.GetName() == html_names::kBackgroundAttr)
      return 0;
    result.attributes_and_values.push_back(
        std::make_pair(attr.LocalName().Impl(), attr.Value()));
  }
  if (result.attributes_and_values.empty())
    return 0;
  // Attribute order doesn't matter. Sort for easy equality comparison.
  std::sort(result.attributes_and_values.begin(),
            result.attributes_and_values.end(), AttributeNameSort);
  // The cache key is non-null when the tagName is set.
  result.tag_name = element.localName().Impl();
  return ComputePresentationAttributeCacheHash(result);
}

CSSPropertyValueSet* ComputePresentationAttributeStyle(Element& element) {
  DCHECK(element.IsStyledElement());

  PresentationAttributeCacheKey cache_key;
  unsigned cache_hash = MakePresentationAttributeCacheKey(element, cache_key);

  PresentationAttributeCache::ValueType* cache_value;
  PresentationAttributeCache& cache = GetPresentationAttributeCache();
  if (cache_hash) {
    cache_value = cache.insert(cache_hash, nullptr).stored_value;
    if (cache_value->value && cache_value->value->key != cache_key)
      cache_hash = 0;
  } else {
    cache_value = nullptr;
  }

  // The element can be cached (has non-zero hash) and has an entry in the
  // cache. Hit.
  if (cache_hash && cache_value->value) {
    // Reference the property set, since if we clean the cache below it may
    // disappear.
    CSSPropertyValueSet* style = cache_value->value->value;

    static const unsigned kMinimumPresentationAttributeCacheSizeForCleaning =
        100;
    if (cache.size() >= kMinimumPresentationAttributeCacheSizeForCleaning)
      cache.clear();
    return style;
  }

  // No entry in the cache or cannot be cached. Miss. Create a new property set.
  CSSPropertyValueSet* style = element.CreatePresentationAttributeStyle();

  // Cannot be cached, so return without inserting into cache.
  if (!cache_hash)
    return style;

  // Have an unpopulated cached entry.
  DCHECK(cache_value);
  DCHECK(!cache_value->value);

  auto* new_entry = MakeGarbageCollected<PresentationAttributeCacheEntry>();
  new_entry->key = cache_key;
  new_entry->value = style;

  static const unsigned kPresentationAttributeCacheMaximumSize = 4096;
  if (cache.size() > kPresentationAttributeCacheMaximumSize) {
    // FIXME: Discarding the entire cache when it gets too big is probably bad
    // since it creates a perf "cliff". Perhaps we should use an LRU?
    cache.clear();
    cache.Set(cache_hash, new_entry);
  } else {
    cache_value->value = new_entry;
  }
  return style;
}

}  // namespace blink