source: branches/4.5.1/doc/src/q3intcache.qdoc@ 1055

/****************************************************************************
**
** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
** Contact: Qt Software Information (qt-info@nokia.com)
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL$
** 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 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.
** $QT_END_LICENSE$
**
****************************************************************************/

/*!
    \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.
*/