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diff --git a/doc/qcache.doc b/doc/qcache.doc new file mode 100644 index 000000000..bc1cd9f06 --- /dev/null +++ b/doc/qcache.doc @@ -0,0 +1,469 @@ +/**************************************************************************** +** +** QCache and QCacheIterator class documentation +** +** Copyright (C) 1992-2008 Trolltech ASA. All rights reserved. +** +** This file is part of the Qt GUI Toolkit. +** +** This file may be used under the terms of the GNU General +** Public License versions 2.0 or 3.0 as published by the Free +** Software Foundation and appearing in the files LICENSE.GPL2 +** and LICENSE.GPL3 included in the packaging of this file. +** Alternatively you may (at your option) use any later version +** of the GNU General Public License if such license has been +** publicly approved by Trolltech ASA (or its successors, if any) +** and the KDE Free Qt Foundation. +** +** Please review the following information to ensure GNU General +** Public Licensing retquirements will be met: +** http://trolltech.com/products/qt/licenses/licensing/opensource/. +** If you are unsure which license is appropriate for your use, please +** review the following information: +** http://trolltech.com/products/qt/licenses/licensing/licensingoverview +** or contact the sales department at sales@trolltech.com. +** +** This file may be used under the terms of the Q Public License as +** defined by Trolltech ASA and appearing in the file LICENSE.QPL +** included in the packaging of this file. Licensees holding valid Qt +** Commercial licenses may use this file in accordance with the Qt +** Commercial License Agreement provided with the Software. +** +** This file is provided "AS IS" with NO WARRANTY OF ANY KIND, +** INCLUDING THE WARRANTIES OF DESIGN, MERCHANTABILITY AND FITNESS FOR +** A PARTICULAR PURPOSE. Trolltech reserves all rights not granted +** herein. +** +**********************************************************************/ + + +/***************************************************************************** + QCache documentation + *****************************************************************************/ + +/*! + \class QCache + \brief The QCache class is a template class that provides a cache based on QString keys. + + \ingroup collection + \ingroup tools + + \important autoDelete setAutoDelete + + A cache is a least recently used (LRU) list of cache items. Each + cache item has a key and a certain cost. The sum of item costs, + totalCost(), never exceeds the maximum cache cost, maxCost(). If + inserting a new item would cause the total cost to exceed the + maximum cost, the least recently used items in the cache are + removed. + + QCache is a template class. QCache\<X\> defines a cache that + operates on pointers to X, or X*. + + Apart from insert(), by far the most important function is find() + (which also exists as operator[]()). This function looks up an + item, returns it, and by default marks it as being the most + recently used item. + + There are also methods to remove() or take() an object from the + cache. Calling setAutoDelete(TRUE) for a cache tells it to delete + items that are removed. The default is to not delete items when + they are removed (i.e., remove() and take() are equivalent). + + When inserting an item into the cache, only the pointer is copied, + not the item itself. This is called a shallow copy. It is possible + to make the cache copy all of the item's data (known as a deep + copy) when an item is inserted. insert() calls the virtual + function QPtrCollection::newItem() for the item to be inserted. + Inherit a cache and reimplement newItem() if you want deep copies. + + When removing a cache item, the virtual function + QPtrCollection::deleteItem() is called. The default + implementation deletes the item if auto-deletion is enabled, and + does nothing otherwise. + + There is a QCacheIterator that can be used to traverse the items + in the cache in arbitrary order. + + In QCache, the cache items are accessed via \l QString keys, which + are Unicode strings. If you want to use non-Unicode, plain 8-bit + \c char* keys, use the QAsciiCache template. A QCache has the + same performance as a QAsciiCache. + + \sa QCacheIterator, QAsciiCache, QIntCache +*/ + +/*! + \fn QCache::QCache( const QCache<type> &c ) + + \internal + + Do not use. A QCache cannot be copied. Calls qFatal() in debug version. +*/ + + +/*! + \fn QCache::QCache( int maxCost, int size, bool caseSensitive ) + + Constructs a cache whose contents will never have a total cost + greater than \a maxCost and which is expected to contain less than + \a size items. + + \a size is actually the size of an internal hash array; it's + usually best to make it a prime number and at least 50% bigger + than the largest expected number of items in the cache. + + Each inserted item has an associated cost. When inserting a new + item, if the total cost of all items in the cache will exceed \a + maxCost, the cache will start throwing out the older (least + recently used) items until there is enough room for the new item + to be inserted. + + If \a caseSensitive is TRUE (the default), the cache keys are case + sensitive; if it is FALSE, they are case-insensitive. + Case-insensitive comparison considers all Unicode letters. +*/ + +/*! + \fn QCache::~QCache() + + Removes all items from the cache and destroys it. All iterators + that access this cache will be reset. +*/ + +/*! + \fn QCache<type>& QCache::operator=( const QCache<type> &c ) + + \internal + + Do not use. A QCache cannot be copied. Calls qFatal() in debug version. +*/ + +/*! + \fn int QCache::maxCost() const + + Returns the maximum allowed total cost of the cache. + + \sa setMaxCost() totalCost() +*/ + +/*! + \fn int QCache::totalCost() const + + Returns the total cost of the items in the cache. This is an + integer in the range 0 to maxCost(). + + \sa setMaxCost() +*/ + +/*! + \fn void QCache::setMaxCost( int m ) + + Sets the maximum allowed total cost of the cache to \a m. If the + current total cost is greater than \a m, some items are deleted + immediately. + + \sa maxCost() totalCost() +*/ + +/*! + \fn uint QCache::count() const + + Returns the number of items in the cache. + + \sa totalCost() +*/ + +/*! + \fn uint QCache::size() const + + Returns the size of the hash array used to implement the cache. + This should be a bit bigger than count() is likely to be. +*/ + +/*! + \fn bool QCache::isEmpty() const + + Returns TRUE if the cache is empty; otherwise returns FALSE. +*/ + +/*! + \fn bool QCache::insert( const QString &k, const type *d, int c, int p ) + + Inserts the item \a d into the cache with key \a k and associated + cost, \a c. Returns TRUE if it is successfully inserted; otherwise + returns FALSE. + + The cache's size is limited, and if the total cost is too high, + QCache will remove old, least recently used items until there is + room for this new item. + + The parameter \a p is internal and should be left at the default + value (0). + + \warning If this function returns FALSE (which could happen, e.g. + if the cost of this item alone exceeds maxCost()) you must delete + \a d yourself. Additionally, be very careful about using \a d + after calling this function because any other insertions into the + cache, from anywhere in the application or within Qt itself, could + cause the object to be discarded from the cache and the pointer to + become invalid. +*/ + +/*! + \fn bool QCache::remove( const QString &k ) + + Removes the item associated with \a k, and returns TRUE if the + item was present in the cache; otherwise returns FALSE. + + The item is deleted if auto-deletion has been enabled, i.e., if + you have called setAutoDelete(TRUE). + + If there are two or more items with equal keys, the one that was + inserted last is removed. + + All iterators that refer to the removed item are set to point to + the next item in the cache's traversal order. + + \sa take(), clear() +*/ + +/*! + \fn type *QCache::take( const QString &k ) + + Takes the item associated with \a k out of the cache without + deleting it, and returns a pointer to the item taken out, or 0 + if the key does not exist in the cache. + + If there are two or more items with equal keys, the one that was + inserted last is taken. + + All iterators that refer to the taken item are set to point to the + next item in the cache's traversal order. + + \sa remove(), clear() +*/ + +/*! + \fn void QCache::clear() + + Removes all items from the cache and deletes them if auto-deletion + has been enabled. + + All cache iterators that operate this on cache are reset. + + \sa remove() take() +*/ + +/*! + \fn type *QCache::find( const QString &k, bool ref ) const + + Returns the item associated with key \a k, or 0 if the key does + not exist in the cache. If \a ref is TRUE (the default), the item + is moved to the front of the least recently used list. + + If there are two or more items with equal keys, the one that was + inserted last is returned. +*/ + +/*! + \fn type *QCache::operator[]( const QString &k ) const + + Returns the item associated with key \a k, or 0 if \a k does not + exist in the cache, and moves the item to the front of the least + recently used list. + + If there are two or more items with equal keys, the one that was + inserted last is returned. + + This is the same as find( k, TRUE ). + + \sa find() +*/ + +/*! + \fn void QCache::statistics() const + + A debug-only utility function. Prints out cache usage, hit/miss, + and distribution information using qDebug(). This function does + nothing in the release library. +*/ + +/***************************************************************************** + QCacheIterator documentation + *****************************************************************************/ + +/*! + \class QCacheIterator qcache.h + \brief The QCacheIterator class provides an iterator for QCache collections. + + \ingroup collection + \ingroup tools + + Note that the traversal order is arbitrary; you are not guaranteed + any particular order. If new objects are inserted into the cache + while the iterator is active, the iterator may or may not see + them. + + Multiple iterators are completely independent, even when they + operate on the same QCache. QCache updates all iterators that + refer an item when that item is removed. + + QCacheIterator provides an operator++(), and an operator+=() to + traverse the cache. The current() and currentKey() functions are + used to access the current cache item and its key. The atFirst() + and atLast() return TRUE if the iterator points to the first or + last item in the cache respectively. The isEmpty() function + returns TRUE if the cache is empty, and count() returns the number + of items in the cache. + + Note that atFirst() and atLast() refer to the iterator's arbitrary + ordering, not to the cache's internal least recently used list. + + \sa QCache +*/ + +/*! + \fn QCacheIterator::QCacheIterator( const QCache<type> &cache ) + + Constructs an iterator for \a cache. The current iterator item is + set to point to the first item in the \a cache. +*/ + +/*! + \fn QCacheIterator::QCacheIterator (const QCacheIterator<type> & ci) + + Constructs an iterator for the same cache as \a ci. The new + iterator starts at the same item as ci.current(), but moves + independently from there on. +*/ + +/*! + \fn QCacheIterator<type>& QCacheIterator::operator=( const QCacheIterator<type> &ci ) + + Makes this an iterator for the same cache as \a ci. The new + iterator starts at the same item as ci.current(), but moves + independently thereafter. +*/ + +/*! + \fn uint QCacheIterator::count() const + + Returns the number of items in the cache on which this iterator + operates. + + \sa isEmpty() +*/ + +/*! + \fn bool QCacheIterator::isEmpty() const + + Returns TRUE if the cache is empty, i.e. count() == 0; otherwise + it returns FALSE. + + \sa count() +*/ + +/*! + \fn bool QCacheIterator::atFirst() const + + Returns TRUE if the iterator points to the first item in the + cache; otherwise returns FALSE. Note that this refers to the + iterator's arbitrary ordering, not to the cache's internal least + recently used list. + + \sa toFirst(), atLast() +*/ + +/*! + \fn bool QCacheIterator::atLast() const + + Returns TRUE if the iterator points to the last item in the cache; + otherwise returns FALSE. Note that this refers to the iterator's + arbitrary ordering, not to the cache's internal least recently + used list. + + \sa toLast(), atFirst() +*/ + +/*! + \fn type *QCacheIterator::toFirst() + + Sets the iterator to point to the first item in the cache and + returns a pointer to the item. + + Sets the iterator to 0 and returns 0 if the cache is empty. + + \sa toLast() isEmpty() +*/ + +/*! + \fn type *QCacheIterator::toLast() + + Sets the iterator to point to the last item in the cache and + returns a pointer to the item. + + Sets the iterator to 0 and returns 0 if the cache is empty. + + \sa toFirst() isEmpty() +*/ + +/*! + \fn QCacheIterator::operator type *() const + + Cast operator. Returns a pointer to the current iterator item. + Same as current(). +*/ + +/*! + \fn type *QCacheIterator::current() const + + Returns a pointer to the current iterator item. +*/ + +/*! + \fn QString QCacheIterator::currentKey() const + + Returns the key for the current iterator item. +*/ + +/*! + \fn type *QCacheIterator::operator()() + + Makes the succeeding item current and returns the original current + item. + + If the current iterator item was the last item in the cache or if + it was 0, 0 is returned. +*/ + +/*! + \fn type *QCacheIterator::operator+=( uint jump ) + + Returns the item \a jump positions after the current item, or 0 if + it is beyond the last item. Makes this the current item. +*/ + +/*! + \fn type *QCacheIterator::operator-=( uint jump ) + + Returns the item \a jump positions before the current item, or 0 + if it is before the first item. Makes this the current item. +*/ + +/*! + \fn type *QCacheIterator::operator++() + + Prefix++ makes the iterator point to the item just after current() + and makes that the new current item for the iterator. If current() + was the last item, operator++() returns 0. +*/ + +/*! + \fn type *QCacheIterator::operator--() + + Prefix-- makes the iterator point to the item just before + current() and makes that the new current item for the iterator. If + current() was the first item, operator--() returns 0. +*/ + |