third_party/WebKit/Source/core/dom/PresentationAttributeStyle.cpp

/*
 * Copyright (C) 2013 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
 * 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,
 * 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.
 */

#include "core/dom/PresentationAttributeStyle.h"

#include "core/css/StylePropertySet.h"
#include "core/dom/Attribute.h"
#include "core/dom/Element.h"
#include "core/html/HTMLInputElement.h"
#include "platform/Timer.h"
#include "wtf/HashFunctions.h"
#include "wtf/HashMap.h"
#include "wtf/text/CString.h"
#include <algorithm>

namespace blink {

using namespace HTMLNames;

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

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

struct PresentationAttributeCacheEntry final
    : public GarbageCollectedFinalized<PresentationAttributeCacheEntry> {
 public:
  DEFINE_INLINE_TRACE() { visitor->trace(value); }

  PresentationAttributeCacheKey key;
  Member<StylePropertySet> value;
};

using PresentationAttributeCache =
    HeapHashMap<unsigned,
                Member<PresentationAttributeCacheEntry>,
                AlreadyHashed>;
static PresentationAttributeCache& presentationAttributeCache() {
  DEFINE_STATIC_LOCAL(PresentationAttributeCache, cache,
                      (new PresentationAttributeCache));
  return cache;
}

class PresentationAttributeCacheCleaner {
  WTF_MAKE_NONCOPYABLE(PresentationAttributeCacheCleaner);
  USING_FAST_MALLOC(PresentationAttributeCacheCleaner);

 public:
  PresentationAttributeCacheCleaner()
      : m_hitCount(0),
        m_cleanTimer(this, &PresentationAttributeCacheCleaner::cleanCache) {}

  void didHitPresentationAttributeCache() {
    if (presentationAttributeCache().size() <
        minimumPresentationAttributeCacheSizeForCleaning)
      return;

    m_hitCount++;

    if (!m_cleanTimer.isActive())
      m_cleanTimer.startOneShot(presentationAttributeCacheCleanTimeInSeconds,
                                BLINK_FROM_HERE);
  }

 private:
  static const unsigned presentationAttributeCacheCleanTimeInSeconds = 60;
  static const unsigned minimumPresentationAttributeCacheSizeForCleaning = 100;
  static const unsigned minimumPresentationAttributeCacheHitCountPerMinute =
      (100 * presentationAttributeCacheCleanTimeInSeconds) / 60;

  void cleanCache(TimerBase* timer) {
    ASSERT_UNUSED(timer, timer == &m_cleanTimer);
    unsigned hitCount = m_hitCount;
    m_hitCount = 0;
    if (hitCount > minimumPresentationAttributeCacheHitCountPerMinute)
      return;
    presentationAttributeCache().clear();
  }

  unsigned m_hitCount;
  Timer<PresentationAttributeCacheCleaner> m_cleanTimer;
};

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 void makePresentationAttributeCacheKey(
    Element& element,
    PresentationAttributeCacheKey& result) {
  // FIXME: Enable for SVG.
  if (!element.isHTMLElement())
    return;
  // Interpretation of the size attributes on <input> depends on the type
  // attribute.
  if (isHTMLInputElement(element))
    return;
  AttributeCollection attributes = element.attributesWithoutUpdate();
  for (const Attribute& attr : attributes) {
    if (!element.isPresentationAttribute(attr.name()))
      continue;
    if (!attr.namespaceURI().isNull())
      return;
    // FIXME: Background URL may depend on the base URL and can't be shared.
    // Disallow caching.
    if (attr.name() == backgroundAttr)
      return;
    result.attributesAndValues.append(
        std::make_pair(attr.localName().impl(), attr.value()));
  }
  if (result.attributesAndValues.isEmpty())
    return;
  // Attribute order doesn't matter. Sort for easy equality comparison.
  std::sort(result.attributesAndValues.begin(),
            result.attributesAndValues.end(), attributeNameSort);
  // The cache key is non-null when the tagName is set.
  result.tagName = element.localName().impl();
}

static unsigned computePresentationAttributeCacheHash(
    const PresentationAttributeCacheKey& key) {
  if (!key.tagName)
    return 0;
  DCHECK(key.attributesAndValues.size());
  unsigned attributeHash = StringHasher::hashMemory(
      key.attributesAndValues.data(),
      key.attributesAndValues.size() * sizeof(key.attributesAndValues[0]));
  return WTF::hashInts(key.tagName->existingHash(), attributeHash);
}

StylePropertySet* computePresentationAttributeStyle(Element& element) {
  DEFINE_STATIC_LOCAL(PresentationAttributeCacheCleaner, cacheCleaner, ());

  DCHECK(element.isStyledElement());

  PresentationAttributeCacheKey cacheKey;
  makePresentationAttributeCacheKey(element, cacheKey);

  unsigned cacheHash = computePresentationAttributeCacheHash(cacheKey);

  PresentationAttributeCache::ValueType* cacheValue;
  if (cacheHash) {
    cacheValue =
        presentationAttributeCache().add(cacheHash, nullptr).storedValue;
    if (cacheValue->value && cacheValue->value->key != cacheKey)
      cacheHash = 0;
  } else {
    cacheValue = nullptr;
  }

  StylePropertySet* style = nullptr;
  if (cacheHash && cacheValue->value) {
    style = cacheValue->value->value;
    cacheCleaner.didHitPresentationAttributeCache();
  } else {
    style = MutableStylePropertySet::create(
        element.isSVGElement() ? SVGAttributeMode : HTMLAttributeMode);
    AttributeCollection attributes = element.attributesWithoutUpdate();
    for (const Attribute& attr : attributes)
      element.collectStyleForPresentationAttribute(
          attr.name(), attr.value(), toMutableStylePropertySet(style));
  }

  if (!cacheHash || cacheValue->value)
    return style;

  PresentationAttributeCacheEntry* newEntry =
      new PresentationAttributeCacheEntry;
  newEntry->key = cacheKey;
  newEntry->value = style;

  static const unsigned presentationAttributeCacheMaximumSize = 4096;
  if (presentationAttributeCache().size() >
      presentationAttributeCacheMaximumSize) {
    // 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?
    presentationAttributeCache().clear();
    presentationAttributeCache().set(cacheHash, newEntry);
  } else {
    cacheValue->value = newEntry;
  }

  return style;
}

}  // namespace blink