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Diffstat (limited to 'src/corelib/tools/qcontiguouscache.cpp')
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diff --git a/src/corelib/tools/qcontiguouscache.cpp b/src/corelib/tools/qcontiguouscache.cpp new file mode 100644 index 0000000..fc75cc0 --- /dev/null +++ b/src/corelib/tools/qcontiguouscache.cpp @@ -0,0 +1,432 @@ +/**************************************************************************** +** +** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies). +** Contact: Qt Software Information (qt-info@nokia.com) +** +** This file is part of the QtCore module of the Qt Toolkit. +** +** $QT_BEGIN_LICENSE:LGPL$ +** No Commercial Usage +** This file contains pre-release code and may not be distributed. +** You may use this file in accordance with the terms and conditions +** contained in the either Technology Preview License Agreement or the +** Beta Release License Agreement. +** +** GNU Lesser General Public License Usage +** Alternatively, this file may be used under the terms of the GNU Lesser +** General Public License version 2.1 as published by the Free Software +** Foundation and appearing in the file LICENSE.LGPL included in the +** packaging of this file. Please review the following information to +** ensure the GNU Lesser General Public License version 2.1 requirements +** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html. +** +** In addition, as a special exception, Nokia gives you certain +** additional rights. These rights are described in the Nokia Qt LGPL +** Exception version 1.0, included in the file LGPL_EXCEPTION.txt in this +** package. +** +** GNU General Public License Usage +** Alternatively, this file may be used under the terms of the GNU +** General Public License version 3.0 as published by the Free Software +** Foundation and appearing in the file LICENSE.GPL included in the +** packaging of this file. Please review the following information to +** ensure the GNU General Public License version 3.0 requirements will be +** met: http://www.gnu.org/copyleft/gpl.html. +** +** If you are unsure which license is appropriate for your use, please +** contact the sales department at qt-sales@nokia.com. +** $QT_END_LICENSE$ +** +****************************************************************************/ + +#include "qcontiguouscache.h" +#ifdef QT_QCONTIGUOUSCACHE_DEBUG +#include <QDebug> +#endif + +QT_BEGIN_NAMESPACE + +#ifdef QT_QCONTIGUOUSCACHE_DEBUG +void QContiguousCacheData::dump() const +{ + qDebug() << "capacity:" << alloc; + qDebug() << "count:" << count; + qDebug() << "start:" << start; + qDebug() << "offset:" << offset; +} +#endif + +/*! \class QContiguousCache + \brief The QContiguousCache class is a template class that provides a contiguous cache. + \ingroup tools + \ingroup shared + \reentrant + + The QContiguousCache class provides an efficient way of caching items for + display in a user interface view. Unlike QCache, it adds a restriction + that elements within the cache are contiguous. This has the advantage + of matching how user interface views most commonly request data, as + a set of rows localized around the current scrolled position. This + restriction allows the cache to consume less memory and processor + cycles than QCache. The QContiguousCache class also can provide + an upper bound on memory usage via setCapacity(). + + The simplest way of using a contiguous cache is to use the append() + and prepend(). + +\code +MyRecord record(int row) const +{ + Q_ASSERT(row >= 0 && row < count()); + + while(row > cache.lastIndex()) + cache.append(slowFetchRecord(cache.lastIndex()+1)); + while(row < cache.firstIndex()) + cache.prepend(slowFetchRecord(cache.firstIndex()-1)); + + return cache.at(row); +} +\endcode + + If the cache is full then the item at the opposite end of the cache from + where the new item is appended or prepended will be removed. + + This usage can be further optimized by using the insert() function + in the case where the requested row is a long way from the currently cached + items. If there is a gap between where the new item is inserted and the currently + cached items then the existing cached items are first removed to retain + the contiguous nature of the cache. Hence it is important to take some care then + when using insert() in order to avoid unwanted clearing of the cache. + + The range of valid indexes for the QContiguousCache class are from + 0 to INT_MAX. Calling prepend() such that the first index would become less + than 0 or append() such that the last index would become greater + than INT_MAX can result in the indexes of the cache being invalid. + When the cache indexes are invalid it is important to call + normalizeIndexes() before calling any of containsIndex(), firstIndex(), + lastIndex(), at() or the [] operator. Calling these + functions when the cache has invalid indexes will result in undefined + behavior. The indexes can be checked by using areIndexesValid() + + In most cases the indexes will not exceed 0 to INT_MAX, and + normalizeIndexes() will not need to be used. + + See the \l{Contiguous Cache Example}{Contiguous Cache} example. +*/ + +/*! \fn QContiguousCache::QContiguousCache(int capacity) + + Constructs a cache with the given \a capacity. + + \sa setCapacity() +*/ + +/*! \fn QContiguousCache::QContiguousCache(const QContiguousCache<T> &other) + + Constructs a copy of \a other. + + This operation takes \l{constant time}, because QContiguousCache is + \l{implicitly shared}. This makes returning a QContiguousCache from a + function very fast. If a shared instance is modified, it will be + copied (copy-on-write), and that takes \l{linear time}. + + \sa operator=() +*/ + +/*! \fn QContiguousCache::~QContiguousCache() + + Destroys the cache. +*/ + +/*! \fn void QContiguousCache::detach() + + \internal +*/ + +/*! \fn bool QContiguousCache::isDetached() const + + \internal +*/ + +/*! \fn void QContiguousCache::setSharable(bool sharable) + + \internal +*/ + +/*! \fn QContiguousCache<T> &QContiguousCache::operator=(const QContiguousCache<T> &other) + + Assigns \a other to this cache and returns a reference to this cache. +*/ + +/*! \fn bool QContiguousCache::operator==(const QContiguousCache<T> &other) const + + Returns true if \a other is equal to this cache; otherwise returns false. + + Two caches are considered equal if they contain the same values at the same + indexes. This function requires the value type to implement the \c operator==(). + + \sa operator!=() +*/ + +/*! \fn bool QContiguousCache::operator!=(const QContiguousCache<T> &other) const + + Returns true if \a other is not equal to this cache; otherwise + returns false. + + Two caches are considered equal if they contain the same values at the same + indexes. This function requires the value type to implement the \c operator==(). + + \sa operator==() +*/ + +/*! \fn int QContiguousCache::capacity() const + + Returns the number of items the cache can store before it is full. + When a cache contains a number of items equal to its capacity, adding new + items will cause items farthest from the added item to be removed. + + \sa setCapacity(), size() +*/ + +/*! \fn int QContiguousCache::count() const + + \overload + + Same as size(). +*/ + +/*! \fn int QContiguousCache::size() const + + Returns the number of items contained within the cache. + + \sa capacity() +*/ + +/*! \fn bool QContiguousCache::isEmpty() const + + Returns true if no items are stored within the cache. + + \sa size(), capacity() +*/ + +/*! \fn bool QContiguousCache::isFull() const + + Returns true if the number of items stored within the cache is equal + to the capacity of the cache. + + \sa size(), capacity() +*/ + +/*! \fn int QContiguousCache::available() const + + Returns the number of items that can be added to the cache before it becomes full. + + \sa size(), capacity(), isFull() +*/ + +/*! \fn void QContiguousCache::clear() + + Removes all items from the cache. The capacity is unchanged. +*/ + +/*! \fn void QContiguousCache::setCapacity(int size) + + Sets the capacity of the cache to the given \a size. A cache can hold a + number of items equal to its capacity. When inserting, appending or prepending + items to the cache, if the cache is already full then the item farthest from + the added item will be removed. + + If the given \a size is smaller than the current count of items in the cache + then only the last \a size items from the cache will remain. + + \sa capacity(), isFull() +*/ + +/*! \fn const T &QContiguousCache::at(int i) const + + Returns the item at index position \a i in the cache. \a i must + be a valid index position in the cache (i.e, firstIndex() <= \a i <= lastIndex()). + + The indexes in the cache refer to the number of positions the item is from the + first item appended into the cache. That is to say a cache with a capacity of + 100, that has had 150 items appended will have a valid index range of + 50 to 149. This allows inserting and retrieving items into the cache based + on a theoretical infinite list + + \sa firstIndex(), lastIndex(), insert(), operator[]() +*/ + +/*! \fn T &QContiguousCache::operator[](int i) + + Returns the item at index position \a i as a modifiable reference. If + the cache does not contain an item at the given index position \a i + then it will first insert an empty item at that position. + + In most cases it is better to use either at() or insert(). + + Note that using non-const operators can cause QContiguousCache to do a deep + copy. + + \sa insert(), at() +*/ + +/*! \fn const T &QContiguousCache::operator[](int i) const + + \overload + + Same as at(\a i). +*/ + +/*! \fn void QContiguousCache::append(const T &value) + + Inserts \a value at the end of the cache. If the cache is already full + the item at the start of the cache will be removed. + + \sa prepend(), insert(), isFull() +*/ + +/*! \fn void QContiguousCache::prepend(const T &value) + + Inserts \a value at the start of the cache. If the cache is already full + the item at the end of the cache will be removed. + + \sa append(), insert(), isFull() +*/ + +/*! \fn void QContiguousCache::insert(int i, const T &value) + + Inserts the \a value at the index position \a i. If the cache already contains + an item at \a i then that value is replaced. If \a i is either one more than + lastIndex() or one less than firstIndex() it is the equivalent to an append() + or a prepend(). + + If the given index \a i is not within the current range of the cache nor adjacent + to the bounds of the cache's index range, the cache is first cleared before + inserting the item. At this point the cache will have a size of 1. It is + worthwhile taking effort to insert items in an order that starts adjacent + to the current index range for the cache. + + The range of valid indexes for the QContiguousCache class are from + 0 to INT_MAX. Inserting outside of this range has undefined behavior. + + + \sa prepend(), append(), isFull(), firstIndex(), lastIndex() +*/ + +/*! \fn bool QContiguousCache::containsIndex(int i) const + + Returns true if the cache's index range includes the given index \a i. + + \sa firstIndex(), lastIndex() +*/ + +/*! \fn int QContiguousCache::firstIndex() const + + Returns the first valid index in the cache. The index will be invalid if the + cache is empty. + + \sa capacity(), size(), lastIndex() +*/ + +/*! \fn int QContiguousCache::lastIndex() const + + Returns the last valid index in the cache. The index will be invalid if the cache is empty. + + \sa capacity(), size(), firstIndex() +*/ + + +/*! \fn T &QContiguousCache::first() + + Returns a reference to the first item in the cache. This function + assumes that the cache isn't empty. + + \sa last(), isEmpty() +*/ + +/*! \fn T &QContiguousCache::last() + + Returns a reference to the last item in the cache. This function + assumes that the cache isn't empty. + + \sa first(), isEmpty() +*/ + +/*! \fn const T& QContiguousCache::first() const + + \overload +*/ + +/*! \fn const T& QContiguousCache::last() const + + \overload +*/ + +/*! \fn void QContiguousCache::removeFirst() + + Removes the first item from the cache. This function assumes that + the cache isn't empty. + + \sa removeLast() +*/ + +/*! \fn void QContiguousCache::removeLast() + + Removes the last item from the cache. This function assumes that + the cache isn't empty. + + \sa removeFirst() +*/ + +/*! \fn T QContiguousCache::takeFirst() + + Removes the first item in the cache and returns it. This function + assumes that the cache isn't empty. + + If you don't use the return value, removeFirst() is more efficient. + + \sa takeLast(), removeFirst() +*/ + +/*! \fn T QContiguousCache::takeLast() + + Removes the last item in the cache and returns it. This function + assumes that the cache isn't empty. + + If you don't use the return value, removeLast() is more efficient. + + \sa takeFirst(), removeLast() +*/ + +/*! \fn void QContiguousCache::normalizeIndexes() + + Moves the first index and last index of the cache + such that they point to valid indexes. The function does not modify + the contents of the cache or the ordering of elements within the cache. + + It is provided so that index overflows can be corrected when using the + cache as a circular buffer. + + \code + QContiguousCache<int> cache(10); + cache.insert(INT_MAX, 1); // cache contains one value and has valid indexes, INT_MAX to INT_MAX + cache.append(2); // cache contains two values but does not have valid indexes. + cache.normalizeIndexes(); // cache has two values, 1 and 2. New first index will be in the range of 0 to capacity(). + \endcode + + \sa areIndexesValid(), append(), prepend() +*/ + +/*! \fn bool QContiguousCache::areIndexesValid() const + + Returns whether the indexes for items stored in the cache are valid. + Indexes can become invalid if items are appended after the index position + INT_MAX or prepended before the index position 0. This is only expected + to occur in very long lived circular buffer style usage of the + contiguous cache. Indexes can be made valid again by calling + normalizeIndexs(). + + \sa normalizeIndexes(), append(), prepend() +*/ + +QT_END_NAMESPACE |