QPatternist::CachingIterator Class Reference

An QAbstractXmlForwardIterator that gets its item from a cache unless its empty, in which case it continues to populate the cache as well as deliver on its own from a source QAbstractXmlForwardIterator. More...

#include <qcachingiterator_p.h>

Inheritance diagram for QPatternist::CachingIterator:

Public Functions
	CachingIterator (ItemSequenceCacheCell::Vector &cacheCells, const VariableSlotID slot, const DynamicContext::Ptr &context)
virtual Item::Iterator::Ptr	copy () const
	Copies this QAbstractXmlForwardIterator and returns the copy. More...
virtual Item	current () const
	Returns the current item in the sequence. More...
virtual Item	next ()
	Returns the next item in the sequence, or a null object if the end has been reached. More...
virtual xsInteger	position () const
	Returns the current position in the sequence represented by this. More...
Public Functions inherited from QAbstractXmlForwardIterator< Item >
virtual qint64	count ()
	Determines the number of items this QAbstractXmlForwardIterator represents. More...
virtual bool	isEmpty ()
	Returns true if the sequence is empty. More...
virtual Item	last ()
	Returns the item at the end of this QAbstractXmlForwardIterator. More...
	QAbstractXmlForwardIterator ()
	Default constructor. More...
virtual qint64	sizeHint () const
	Gives a hint to the size of the contained sequence. More...
virtual QList< Item >	toList ()
	Performs a copy of this QAbstractXmlForwardIterator(with copy()), and returns its items in a QList. More...
virtual QAbstractXmlForwardIterator< Item >::Ptr	toReversed ()
	Returns a reverse iterator for the sequence. More...
virtual	~QAbstractXmlForwardIterator ()
	Destructor. More...
Public Functions inherited from QSharedData
	QSharedData ()
	Constructs a QSharedData object with a reference count of 0. More...
	QSharedData (const QSharedData &)
	Constructs a QSharedData object with reference count 0. More...

Properties
ItemSequenceCacheCell::Vector &	m_cacheCells
const DynamicContext::Ptr	m_context
Item	m_current
xsInteger	m_position
bool	m_usingCache
const VariableSlotID	m_varSlot

Additional Inherited Members
Public Types inherited from QAbstractXmlForwardIterator< Item >
typedef QList< QExplicitlySharedDataPointer< QAbstractXmlForwardIterator< Item > > >	List
	A QList containing QAbstractXmlForwardIterator::Ptr instances. More...
typedef QExplicitlySharedDataPointer< QAbstractXmlForwardIterator< Item > >	Ptr
	A smart pointer wrapping an instance of a QAbstractXmlForwardIterator subclass. More...
typedef QVector< QExplicitlySharedDataPointer< QAbstractXmlForwardIterator< Item > > >	Vector
	A QVector containing QAbstractXmlForwardIterator::Ptr instances. More...
Public Variables inherited from QSharedData
QAtomicInt	ref
Related Functions inherited from QAbstractXmlForwardIterator< Item >
static QAbstractXmlForwardIterator< TResult >::Ptr	makeSequenceMappingIterator (const TMapper &mapper, const QExplicitlySharedDataPointer< QAbstractXmlForwardIterator< TSource > > &source, const DynamicContext::Ptr &context)
	An object generator for SequenceMappingIterator. More...
bool	qIsForwardIteratorEnd (const Item &unit)
	The Callback QAbstractXmlForwardIterator uses for determining whether unit is the end of a sequence. More...

Detailed Description

An QAbstractXmlForwardIterator that gets its item from a cache unless its empty, in which case it continues to populate the cache as well as deliver on its own from a source QAbstractXmlForwardIterator.

Author

Frans Englich frans.nosp@m..fra.nosp@m.ns.en.nosp@m.glic.nosp@m.h@nok.nosp@m.ia.c.nosp@m.om

Definition at line 75 of file qcachingiterator_p.h.

Constructors and Destructors

CachingIterator()

CachingIterator::CachingIterator	(	ItemSequenceCacheCell::Vector &	cacheCells,
		const VariableSlotID	slot,
		const DynamicContext::Ptr &	context
	)

We always use the same cache cell so why don't we use it directly, instead of passing the slot and ItemSequenceCacheCell::Vector to this class? Because the GenericDynamicContext might decide to resize the vector and that would invalidate the reference.

We intentionally pass in a non-const reference here.

Definition at line 50 of file qcachingiterator.cpp.

Referenced by copy().

                                                                   : m_position(0),
                                                                       m_varSlot(slot),
                                                                       m_context(context),
                                                                       m_cacheCells(cacheCells),
                                                                       m_usingCache(true)
{
    Q_ASSERT(m_varSlot > -1);
    Q_ASSERT(m_context);
    Q_ASSERT(m_cacheCells.at(m_varSlot).sourceIterator);
    Q_ASSERT_X((m_cacheCells.at(m_varSlot).cachedItems.isEmpty() && m_cacheCells.at(m_varSlot).cacheState == ItemSequenceCacheCell::Empty) ||
               m_cacheCells.at(m_varSlot).cacheState == ItemSequenceCacheCell::PartiallyPopulated,
               Q_FUNC_INFO,
               "It makes no sense to construct a CachingIterator for a cache that is ItemSequenceCacheCell::Full.");
}

Functions

copy()

Item::Iterator::Ptr CachingIterator::copy ( ) const

virtual

Copies this QAbstractXmlForwardIterator and returns the copy.

Warning

This function is not part of the public interface.

A copy and the original instance are completely independent of each other. Because evaluating an QAbstractXmlForwardIterator modifies it, one should always use a copy when an QAbstractXmlForwardIterator needs to be used several times.

Reimplemented from QAbstractXmlForwardIterator< Item >.

Definition at line 121 of file qcachingiterator.cpp.

{
    const ItemSequenceCacheCell &cell = m_cacheCells.at(m_varSlot);
    if(cell.cacheState == ItemSequenceCacheCell::Full)
        return makeListIterator(cell.cachedItems);
    else
        return Item::Iterator::Ptr(new CachingIterator(m_cacheCells, m_varSlot, m_context));
}

current()

Item CachingIterator::current ( ) const

virtual

Returns the current item in the sequence.

If this function is called before the first call to next(), a null object is returned. If the end of the sequence has been reached, a null object is returned.

Implements QAbstractXmlForwardIterator< Item >.

Definition at line 111 of file qcachingiterator.cpp.

{
    return m_current;
}

next()

Item CachingIterator::next ( )

virtual

Returns the next item in the sequence, or a null object if the end has been reached.

Implements QAbstractXmlForwardIterator< Item >.

Definition at line 67 of file qcachingiterator.cpp.

{
    ItemSequenceCacheCell &cell = m_cacheCells[m_varSlot];
    if(m_position == -1)
        return Item();

    if(m_usingCache)
    {
        ++m_position;

        /* QAbstractXmlForwardIterator::position() starts at 1, while Qt's container classes
         * starts at 0. */
        if(m_position - 1 < cell.cachedItems.count())
        {
            m_current = cell.cachedItems.at(m_position - 1);
            return m_current;
        }
        else
        {
            cell.cacheState = ItemSequenceCacheCell::PartiallyPopulated;
            m_usingCache = false;
            /* We decrement here so we don't have to add a branch for this
             * when using the source QAbstractXmlForwardIterator below. */
            --m_position;
        }
    }

    m_current = cell.sourceIterator->next();

    if(m_current)
    {
        cell.cachedItems.append(m_current);
        Q_ASSERT(cell.cacheState == ItemSequenceCacheCell::PartiallyPopulated);
        ++m_position;
        return m_current;
    }
    else
    {
        m_position = -1;
        cell.cacheState = ItemSequenceCacheCell::Full;
        return Item();
    }
}

position()

xsInteger CachingIterator::position ( ) const

virtual

Returns the current position in the sequence represented by this.

The first position is 1, not 0. If next() hasn't been called, 0 is returned. If this has reached the end, -1 is returned.

Implements QAbstractXmlForwardIterator< Item >.

Definition at line 116 of file qcachingiterator.cpp.

{
    return m_position;
}

Properties

m_cacheCells

ItemSequenceCacheCell::Vector& QPatternist::CachingIterator::m_cacheCells

private

We intentionally store a reference here such that we are able to modify the item.

Definition at line 115 of file qcachingiterator_p.h.

Referenced by CachingIterator(), copy(), and next().

m_context

const DynamicContext::Ptr QPatternist::CachingIterator::m_context

private

We don't use the context. We only keep a reference such that it doesn't get deleted, and m_cacheCells starts to dangle.

Definition at line 109 of file qcachingiterator_p.h.

Referenced by CachingIterator(), and copy().

m_current

Item QPatternist::CachingIterator::m_current

private

Definition at line 96 of file qcachingiterator_p.h.

Referenced by current(), and next().

m_position

xsInteger QPatternist::CachingIterator::m_position

private

Definition at line 97 of file qcachingiterator_p.h.

Referenced by next(), and position().

m_usingCache

bool QPatternist::CachingIterator::m_usingCache

private

Whether this CachingIterator is delivering items from m_cacheCell.cacheItems or from m_cacheCell.sourceIterator.

Definition at line 121 of file qcachingiterator_p.h.

Referenced by next().

m_varSlot

const VariableSlotID QPatternist::CachingIterator::m_varSlot

private

This variable cannot be called m_slot, because /usr/include/sys/sysmacros.h on hpuxi-acc defines it.

Definition at line 103 of file qcachingiterator_p.h.

Referenced by CachingIterator(), copy(), and next().

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The documentation for this class was generated from the following files:

• /src/xmlpatterns/iterators/qcachingiterator_p.h
• /src/xmlpatterns/iterators/qcachingiterator.cpp