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+++ b/src/qt3support/tools/q3intcache.qdoc Mon Jan 11 14:00:40 2010 +0000
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+/****************************************************************************
+**
+** Copyright (C) 2009 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.
+**
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+** 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 Technology Preview License Agreement accompanying
+** this package.
+**
+** GNU Lesser General Public License Usage
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+** General Public License version 2.1 as published by the Free Software
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+** 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
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+**
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+**
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+**
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+/*!
+ \class Q3IntCache
+ \brief The Q3IntCache class is a template class that provides a cache based on long keys.
+ \compat
+
+ Q3IntCache is implemented as a template class. Define a template
+ instance Q3IntCache\<X\> to create a cache that operates on
+ pointers to X, or X*.
+
+ A cache is a least recently used (LRU) list of cache items,
+ accessed via \c long keys. Each cache item has a cost. The sum
+ of item costs, totalCost(), will not exceed 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.
+
+ 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 dictionary and reimplement newItem() if you want deep
+ copies.
+
+ When removing a cache item, the item will be automatically
+ deleted if auto-deletion is enabled.
+
+ There is a Q3IntCacheIterator which may be used to traverse the
+ items in the cache in arbitrary order.
+
+ \sa Q3IntCacheIterator, Q3Cache, Q3AsciiCache
+*/
+
+/*!
+ \fn Q3IntCache::Q3IntCache( const Q3IntCache<type> &c )
+
+ \internal
+
+ Do not use. A Q3IntCache cannot be copied. Calls qFatal() in debug version.
+*/
+
+/*!
+ \fn Q3IntCache::Q3IntCache( int maxCost, int size )
+
+ 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 prime and at least 50% bigger than the
+ largest expected number of items in the cache.
+
+ Each inserted item is associated with a 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.
+*/
+
+/*!
+ \fn Q3IntCache::~Q3IntCache()
+
+ Removes all items from the cache and then destroys the int cache.
+ If auto-deletion is enabled the cache's items are deleted. All
+ iterators that access this cache will be reset.
+*/
+
+/*!
+ \fn Q3IntCache<type>& Q3IntCache::operator=( const Q3IntCache<type> &c )
+
+ \internal
+
+ Do not use. A Q3IntCache cannot be copied. Calls qFatal() in debug version.
+*/
+
+/*!
+ \fn int Q3IntCache::maxCost() const
+
+ Returns the maximum allowed total cost of the cache.
+
+ \sa setMaxCost() totalCost()
+*/
+
+/*!
+ \fn int Q3IntCache::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 Q3IntCache::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 removed
+ immediately.
+
+ \sa maxCost() totalCost()
+*/
+
+/*!
+ \fn uint Q3IntCache::count() const
+
+ Returns the number of items in the cache.
+
+ \sa totalCost()
+*/
+
+/*!
+ \fn uint Q3IntCache::size() const
+
+ Returns the size of the hash array used to implement the cache.
+ This should be a bit larger than count() is likely to be.
+*/
+
+/*!
+ \fn bool Q3IntCache::isEmpty() const
+
+ Returns TRUE if the cache is empty; otherwise returns FALSE.
+*/
+
+/*!
+ \fn bool Q3IntCache::insert( long k, const type *d, int c, int p )
+
+ Inserts the item \a d into the cache with key \a k and assigns it
+ a cost of \a c (default 1). Returns TRUE if it succeeds; otherwise
+ returns FALSE.
+
+ The cache's size is limited, and if the total cost is too high,
+ Q3IntCache will remove old, least-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 (for example, the cost \c,
+ exceeds maxCost()), you must delete \a d yourself. Additionally,
+ be very careful about using \a d after calling this function. 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 Q3IntCache::remove( long 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 most recently 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 * Q3IntCache::take( long 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 most recently 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 Q3IntCache::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 * Q3IntCache::find( long k, bool ref ) const
+
+ Returns the item associated with \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 most recently is returned.
+*/
+
+/*!
+ \fn type * Q3IntCache::operator[]( long k ) const
+
+ Returns the item associated with \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 most recently is returned.
+
+ This is the same as find( k, TRUE ).
+
+ \sa find()
+*/
+
+/*!
+ \fn void Q3IntCache::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.
+*/
+
+/*!
+ \class Q3IntCacheIterator
+ \brief The Q3IntCacheIterator class provides an iterator for Q3IntCache 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 Q3IntCache. Q3IntCache updates all iterators
+ that refer an item when that item is removed.
+
+ Q3IntCacheIterator provides an operator++(), and an operator+=() to
+ traverse the cache; current() and currentKey() to access the
+ current cache item and its key; atFirst() atLast(), which return
+ TRUE if the iterator points to the first/last item in the cache;
+ isEmpty(), which returns TRUE if the cache is empty; and count(),
+ which 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 Q3IntCache
+*/
+
+/*!
+ \fn Q3IntCacheIterator::Q3IntCacheIterator( const Q3IntCache<type> &cache )
+
+ Constructs an iterator for \a cache. The current iterator item is
+ set to point to the first item in the \a cache (or rather, the
+ first item is defined to be the item at which this constructor
+ sets the iterator to point).
+*/
+
+/*!
+ \fn Q3IntCacheIterator::Q3IntCacheIterator (const Q3IntCacheIterator<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 Q3IntCacheIterator<type>& Q3IntCacheIterator::operator=( const Q3IntCacheIterator<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 Q3IntCacheIterator::count() const
+
+ Returns the number of items in the cache on which this iterator
+ operates.
+
+ \sa isEmpty()
+*/
+
+/*!
+ \fn bool Q3IntCacheIterator::isEmpty() const
+
+ Returns TRUE if the cache is empty; otherwise returns FALSE.
+
+ \sa count()
+*/
+
+/*!
+ \fn bool Q3IntCacheIterator::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 Q3IntCacheIterator::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 *Q3IntCacheIterator::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 *Q3IntCacheIterator::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 Q3IntCacheIterator::operator type *() const
+
+ Cast operator. Returns a pointer to the current iterator item.
+ Same as current().
+*/
+
+/*!
+ \fn type *Q3IntCacheIterator::current() const
+
+ Returns a pointer to the current iterator item.
+*/
+
+/*!
+ \fn long Q3IntCacheIterator::currentKey() const
+
+ Returns the key for the current iterator item.
+*/
+
+/*!
+ \fn type *Q3IntCacheIterator::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 *Q3IntCacheIterator::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 *Q3IntCacheIterator::operator-=( uint jump )
+
+ Returns the item \a jump positions before the current item, or 0
+ if it is beyond the first item. Makes this the current item.
+*/
+
+/*!
+ \fn type *Q3IntCacheIterator::operator++()
+
+ Prefix ++ makes the iterator point to the item just after
+ current(), and makes it the new current item for the iterator. If
+ current() was the last item, operator--() returns 0.
+*/
+
+/*!
+ \fn type *Q3IntCacheIterator::operator--()
+
+ Prefix -- makes the iterator point to the item just before
+ current(), and makes it the new current item for the iterator. If
+ current() was the first item, operator--() returns 0.
+*/