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/*
* Copyright (C) 2013, 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:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. 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.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS 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 APPLE INC. OR ITS 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.
*/
#ifndef CollectionIndexCache_h
#define CollectionIndexCache_h
#include <wtf/Vector.h>
namespace WebCore {
void reportExtraMemoryCostForCollectionIndexCache(size_t);
template <class Collection, class Iterator>
class CollectionIndexCache {
public:
explicit CollectionIndexCache(const Collection&);
typedef typename std::iterator_traits<Iterator>::value_type NodeType;
unsigned nodeCount(const Collection&);
NodeType* nodeAt(const Collection&, unsigned index);
bool hasValidCache(const Collection& collection) const { return m_current != collection.collectionEnd() || m_nodeCountValid || m_listValid; }
void invalidate(const Collection&);
size_t memoryCost() { return m_cachedList.capacity() * sizeof(NodeType*); }
private:
unsigned computeNodeCountUpdatingListCache(const Collection&);
NodeType* traverseBackwardTo(const Collection&, unsigned);
NodeType* traverseForwardTo(const Collection&, unsigned);
Iterator m_current;
unsigned m_currentIndex;
unsigned m_nodeCount;
Vector<NodeType*> m_cachedList;
bool m_nodeCountValid : 1;
bool m_listValid : 1;
};
template <class Collection, class Iterator>
inline CollectionIndexCache<Collection, Iterator>::CollectionIndexCache(const Collection& collection)
: m_current(collection.collectionEnd())
, m_currentIndex(0)
, m_nodeCount(0)
, m_nodeCountValid(false)
, m_listValid(false)
{
}
template <class Collection, class Iterator>
inline unsigned CollectionIndexCache<Collection, Iterator>::nodeCount(const Collection& collection)
{
if (!m_nodeCountValid) {
if (!hasValidCache(collection))
collection.willValidateIndexCache();
m_nodeCount = computeNodeCountUpdatingListCache(collection);
m_nodeCountValid = true;
}
return m_nodeCount;
}
template <class Collection, class Iterator>
unsigned CollectionIndexCache<Collection, Iterator>::computeNodeCountUpdatingListCache(const Collection& collection)
{
auto current = collection.collectionBegin();
auto end = collection.collectionEnd();
if (current == end)
return 0;
unsigned oldCapacity = m_cachedList.capacity();
while (current != end) {
m_cachedList.append(&*current);
unsigned traversed;
collection.collectionTraverseForward(current, 1, traversed);
ASSERT(traversed == (current != end ? 1 : 0));
}
m_listValid = true;
if (unsigned capacityDifference = m_cachedList.capacity() - oldCapacity)
reportExtraMemoryCostForCollectionIndexCache(capacityDifference * sizeof(NodeType*));
return m_cachedList.size();
}
template <class Collection, class Iterator>
inline typename CollectionIndexCache<Collection, Iterator>::NodeType* CollectionIndexCache<Collection, Iterator>::traverseBackwardTo(const Collection& collection, unsigned index)
{
ASSERT(m_current != collection.collectionEnd());
ASSERT(index < m_currentIndex);
bool firstIsCloser = index < m_currentIndex - index;
if (firstIsCloser || !collection.collectionCanTraverseBackward()) {
m_current = collection.collectionBegin();
m_currentIndex = 0;
if (index)
collection.collectionTraverseForward(m_current, index, m_currentIndex);
ASSERT(m_current != collection.collectionEnd());
return &*m_current;
}
collection.collectionTraverseBackward(m_current, m_currentIndex - index);
m_currentIndex = index;
ASSERT(m_current != collection.collectionEnd());
return &*m_current;
}
template <class Collection, class Iterator>
inline typename CollectionIndexCache<Collection, Iterator>::NodeType* CollectionIndexCache<Collection, Iterator>::traverseForwardTo(const Collection& collection, unsigned index)
{
ASSERT(m_current != collection.collectionEnd());
ASSERT(index > m_currentIndex);
ASSERT(!m_nodeCountValid || index < m_nodeCount);
bool lastIsCloser = m_nodeCountValid && m_nodeCount - index < index - m_currentIndex;
if (lastIsCloser && collection.collectionCanTraverseBackward()) {
ASSERT(hasValidCache(collection));
m_current = collection.collectionLast();
if (index < m_nodeCount - 1)
collection.collectionTraverseBackward(m_current, m_nodeCount - index - 1);
m_currentIndex = index;
ASSERT(m_current != collection.collectionEnd());
return &*m_current;
}
if (!hasValidCache(collection))
collection.willValidateIndexCache();
unsigned traversedCount;
collection.collectionTraverseForward(m_current, index - m_currentIndex, traversedCount);
m_currentIndex = m_currentIndex + traversedCount;
if (m_current == collection.collectionEnd()) {
ASSERT(m_currentIndex < index);
// Failed to find the index but at least we now know the size.
m_nodeCount = m_currentIndex + 1;
m_nodeCountValid = true;
return nullptr;
}
ASSERT(hasValidCache(collection));
return &*m_current;
}
template <class Collection, class Iterator>
inline typename CollectionIndexCache<Collection, Iterator>::NodeType* CollectionIndexCache<Collection, Iterator>::nodeAt(const Collection& collection, unsigned index)
{
if (m_nodeCountValid && index >= m_nodeCount)
return nullptr;
if (m_listValid)
return m_cachedList[index];
auto end = collection.collectionEnd();
if (m_current != end) {
if (index > m_currentIndex)
return traverseForwardTo(collection, index);
if (index < m_currentIndex)
return traverseBackwardTo(collection, index);
return &*m_current;
}
bool lastIsCloser = m_nodeCountValid && m_nodeCount - index < index;
if (lastIsCloser && collection.collectionCanTraverseBackward()) {
ASSERT(hasValidCache(collection));
m_current = collection.collectionLast();
if (index < m_nodeCount - 1)
collection.collectionTraverseBackward(m_current, m_nodeCount - index - 1);
m_currentIndex = index;
ASSERT(m_current != end);
return &*m_current;
}
if (!hasValidCache(collection))
collection.willValidateIndexCache();
m_current = collection.collectionBegin();
m_currentIndex = 0;
if (index && m_current != end) {
collection.collectionTraverseForward(m_current, index, m_currentIndex);
ASSERT(m_current != end || m_currentIndex < index);
}
if (m_current == end) {
// Failed to find the index but at least we now know the size.
m_nodeCount = m_currentIndex + 1;
m_nodeCountValid = true;
return nullptr;
}
ASSERT(hasValidCache(collection));
return &*m_current;
}
template <class Collection, class Iterator>
void CollectionIndexCache<Collection, Iterator>::invalidate(const Collection& collection)
{
m_current = collection.collectionEnd();
m_nodeCountValid = false;
m_listValid = false;
m_cachedList.shrink(0);
}
}
#endif
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