/**************************************************************************** ** ** Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies). ** All rights reserved. ** Contact: Nokia Corporation (qt-info@nokia.com) ** ** This file is part of the documentation of the Qt Toolkit. ** ** $QT_BEGIN_LICENSE:FDL$ ** Commercial Usage ** Licensees holding valid Qt Commercial licenses may use this file in ** accordance with the Qt Commercial License Agreement provided with the ** Software or, alternatively, in accordance with the terms contained in a ** written agreement between you and Nokia. ** ** GNU Free Documentation License ** Alternatively, this file may be used under the terms of the GNU Free ** Documentation License version 1.3 as published by the Free Software ** Foundation and appearing in the file included in the packaging of this ** file. ** ** If you have questions regarding the use of this file, please contact ** Nokia at qt-info@nokia.com. ** $QT_END_LICENSE$ ** ****************************************************************************/ /*! \class Q3Cache \brief The Q3Cache class is a template class that provides a cache based on QString keys. \compat 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. Q3Cache is a template class. Q3Cache\ 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 Q3PtrCollection::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 Q3PtrCollection::deleteItem() is called. The default implementation deletes the item if auto-deletion is enabled, and does nothing otherwise. There is a Q3CacheIterator that can be used to traverse the items in the cache in arbitrary order. In Q3Cache, the cache items are accessed via QString keys, which are Unicode strings. If you want to use non-Unicode, plain 8-bit \c char* keys, use the Q3AsciiCache template. A Q3Cache has the same performance as a Q3AsciiCache. \sa Q3CacheIterator, Q3AsciiCache, Q3IntCache */ /*! \fn Q3Cache::Q3Cache( const Q3Cache &c ) \internal Do not use. A Q3Cache cannot be copied. Calls qFatal() in debug version. */ /*! \fn Q3Cache::Q3Cache( 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 Q3Cache::~Q3Cache() Removes all items from the cache and destroys it. All iterators that access this cache will be reset. */ /*! \fn Q3Cache& Q3Cache::operator=( const Q3Cache &c ) \internal Do not use. A Q3Cache cannot be copied. Calls qFatal() in debug version. */ /*! \fn int Q3Cache::maxCost() const Returns the maximum allowed total cost of the cache. \sa setMaxCost() totalCost() */ /*! \fn int Q3Cache::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 Q3Cache::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 Q3Cache::count() const Returns the number of items in the cache. \sa totalCost() */ /*! \fn uint Q3Cache::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 Q3Cache::isEmpty() const Returns TRUE if the cache is empty; otherwise returns FALSE. */ /*! \fn bool Q3Cache::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, Q3Cache 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 Q3Cache::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 *Q3Cache::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 Q3Cache::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 *Q3Cache::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 *Q3Cache::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 Q3Cache::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. */ /***************************************************************************** Q3CacheIterator documentation *****************************************************************************/ /*! \class Q3CacheIterator qcache.h \brief The Q3CacheIterator class provides an iterator for Q3Cache collections. \compat 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 Q3Cache. Q3Cache updates all iterators that refer an item when that item is removed. Q3CacheIterator 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 Q3Cache */ /*! \fn Q3CacheIterator::Q3CacheIterator( const Q3Cache &cache ) Constructs an iterator for \a cache. The current iterator item is set to point to the first item in the \a cache. */ /*! \fn Q3CacheIterator::Q3CacheIterator (const Q3CacheIterator & 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 Q3CacheIterator& Q3CacheIterator::operator=( const Q3CacheIterator &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 Q3CacheIterator::count() const Returns the number of items in the cache on which this iterator operates. \sa isEmpty() */ /*! \fn bool Q3CacheIterator::isEmpty() const Returns TRUE if the cache is empty, i.e. count() == 0; otherwise it returns FALSE. \sa count() */ /*! \fn bool Q3CacheIterator::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 Q3CacheIterator::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 *Q3CacheIterator::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 *Q3CacheIterator::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 Q3CacheIterator::operator type *() const Cast operator. Returns a pointer to the current iterator item. Same as current(). */ /*! \fn type *Q3CacheIterator::current() const Returns a pointer to the current iterator item. */ /*! \fn QString Q3CacheIterator::currentKey() const Returns the key for the current iterator item. */ /*! \fn type *Q3CacheIterator::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 *Q3CacheIterator::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 *Q3CacheIterator::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 *Q3CacheIterator::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 *Q3CacheIterator::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. */