1// Copyright (C) 2016 The Qt Company Ltd.
2// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
3
4#include "qcontiguouscache.h"
5#ifdef QT_QCONTIGUOUSCACHE_DEBUG
6#include <QDebug>
7#endif
8
9#include <QtCore/qmalloc.h>
10
11QT_BEGIN_NAMESPACE
12
13#ifdef QT_QCONTIGUOUSCACHE_DEBUG
14void QContiguousCacheData::dump() const
15{
16 qDebug() << "capacity:" << alloc;
17 qDebug() << "count:" << count;
18 qDebug() << "start:" << start;
19 qDebug() << "offset:" << offset;
20}
21#endif
22
23QContiguousCacheData *QContiguousCacheData::allocateData(qsizetype size, qsizetype alignment)
24{
25 void *mem = qMallocAligned(size: size_t(size), alignment: size_t(alignment));
26 return new (mem) QContiguousCacheData{/*ref=*/1, .alloc: 0, .count: 0, .start: 0, .offset: 0};
27}
28
29void QContiguousCacheData::freeData(QContiguousCacheData *data)
30{
31 qFreeAligned(ptr: data);
32}
33
34/*! \class QContiguousCache
35 \inmodule QtCore
36 \brief The QContiguousCache class is a template class that provides a contiguous cache.
37 \ingroup tools
38 \ingroup shared
39 \reentrant
40 \since 4.6
41
42 The QContiguousCache class provides an efficient way of caching items for
43 display in a user interface view. Unlike QCache, it adds a restriction
44 that elements within the cache are contiguous. This has the advantage
45 of matching how user interface views most commonly request data, as
46 a set of rows localized around the current scrolled position. This
47 restriction allows the cache to consume less memory and processor
48 cycles than QCache.
49
50 QContiguousCache operates on a fixed capacity, set with setCapacity() or
51 passed as a parameter to the constructor. This capacity is the upper bound
52 on memory usage by the cache itself, not including the memory allocated by
53 the elements themselves. Note that a cache with a capacity of zero (the
54 default) means no items will be stored: the insert(), append() and
55 prepend() operations will effectively be no-ops. Therefore, it's important
56 to set the capacity to a reasonable value before adding items to the cache.
57
58 The simplest way of using a contiguous cache is to use the append()
59 and prepend().
60
61 \snippet code/src_corelib_tools_qcontiguouscache.cpp 0
62
63 If the cache is full then the item at the opposite end of the cache from
64 where the new item is appended or prepended will be removed.
65
66 This usage can be further optimized by using the insert() function
67 in the case where the requested row is a long way from the currently cached
68 items. If there is a gap between where the new item is inserted and the currently
69 cached items then the existing cached items are first removed to retain
70 the contiguous nature of the cache. Hence it is important to take some care then
71 when using insert() in order to avoid unwanted clearing of the cache.
72
73 The range of valid indexes for the QContiguousCache class are from
74 0 to INT_MAX. Calling prepend() such that the first index would become less
75 than 0 or append() such that the last index would become greater
76 than INT_MAX can result in the indexes of the cache being invalid.
77 When the cache indexes are invalid it is important to call
78 normalizeIndexes() before calling any of containsIndex(), firstIndex(),
79 lastIndex(), at() or \l{QContiguousCache::operator[]()}{operator[]()}.
80 Calling these functions when the cache has invalid indexes will result in
81 undefined behavior. The indexes can be checked by using areIndexesValid()
82
83 In most cases the indexes will not exceed 0 to INT_MAX, and
84 normalizeIndexes() will not need to be used.
85
86 See the \l{Contiguous Cache Example}{Contiguous Cache} example.
87*/
88
89/*! \fn template<typename T> QContiguousCache<T>::QContiguousCache(qsizetype capacity)
90
91 Constructs a cache with the given \a capacity.
92
93 \sa setCapacity()
94*/
95
96/*! \fn template<typename T> QContiguousCache<T>::QContiguousCache(const QContiguousCache<T> &other)
97
98 Constructs a copy of \a other.
99
100 This operation takes \l{constant time}, because QContiguousCache is
101 \l{implicitly shared}. This makes returning a QContiguousCache from a
102 function very fast. If a shared instance is modified, it will be
103 copied (copy-on-write), and that takes \l{linear time}.
104
105 \sa operator=()
106*/
107
108/*! \fn template<typename T> QContiguousCache<T>::~QContiguousCache()
109
110 Destroys the cache.
111*/
112
113/*! \fn template<typename T> void QContiguousCache<T>::detach()
114 \internal
115*/
116
117/*! \fn template<typename T> bool QContiguousCache<T>::isDetached() const
118 \internal
119*/
120
121/*! \fn template<typename T> void QContiguousCache<T>::setSharable(bool sharable)
122 \internal
123*/
124
125/*! \typedef QContiguousCache::value_type
126 \internal
127 */
128
129/*! \typedef QContiguousCache::pointer
130 \internal
131 */
132
133/*! \typedef QContiguousCache::const_pointer
134 \internal
135 */
136
137/*! \typedef QContiguousCache::reference
138 \internal
139 */
140
141/*! \typedef QContiguousCache::const_reference
142 \internal
143 */
144
145/*! \typedef QContiguousCache::difference_type
146 \internal
147 */
148
149/*! \typedef QContiguousCache::size_type
150 \internal
151 */
152
153/*! \fn template<typename T> QContiguousCache<T> &QContiguousCache<T>::operator=(const QContiguousCache<T> &other)
154
155 Assigns \a other to this cache and returns a reference to this cache.
156*/
157
158/*!
159 \fn template<typename T> QContiguousCache<T> &QContiguousCache<T>::operator=(QContiguousCache<T> &&other)
160
161 Move-assigns \a other to this QContiguousCache instance.
162
163 \since 5.2
164*/
165
166/*! \fn template<typename T> void QContiguousCache<T>::swap(QContiguousCache<T> &other)
167 \since 4.8
168 \memberswap{cache}
169*/
170
171/*! \fn template<typename T> bool QContiguousCache<T>::operator==(const QContiguousCache<T> &other) const
172
173 Returns \c true if \a other is equal to this cache; otherwise returns \c false.
174
175 Two caches are considered equal if they contain the same values at the same
176 indexes. This function requires the value type to implement the \c operator==().
177
178 \sa operator!=()
179*/
180
181/*! \fn template<typename T> bool QContiguousCache<T>::operator!=(const QContiguousCache<T> &other) const
182
183 Returns \c true if \a other is not equal to this cache; otherwise
184 returns \c false.
185
186 Two caches are considered equal if they contain the same values at the same
187 indexes. This function requires the value type to implement the \c operator==().
188
189 \sa operator==()
190*/
191
192/*! \fn template<typename T> qsizetype QContiguousCache<T>::capacity() const
193
194 Returns the number of items the cache can store before it is full.
195 When a cache contains a number of items equal to its capacity, adding new
196 items will cause items farthest from the added item to be removed.
197
198 \sa setCapacity(), size()
199*/
200
201/*! \fn template<typename T> qsizetype QContiguousCache<T>::count() const
202
203 Same as size().
204*/
205
206/*! \fn template<typename T> qsizetype QContiguousCache<T>::size() const
207
208 Returns the number of items contained within the cache.
209
210 \sa capacity()
211*/
212
213/*! \fn template<typename T> bool QContiguousCache<T>::isEmpty() const
214
215 Returns \c true if no items are stored within the cache.
216
217 \sa size(), capacity()
218*/
219
220/*! \fn template<typename T> bool QContiguousCache<T>::isFull() const
221
222 Returns \c true if the number of items stored within the cache is equal
223 to the capacity of the cache.
224
225 \sa size(), capacity()
226*/
227
228/*! \fn template<typename T> qsizetype QContiguousCache<T>::available() const
229
230 Returns the number of items that can be added to the cache before it becomes full.
231
232 \sa size(), capacity(), isFull()
233*/
234
235/*! \fn template<typename T> void QContiguousCache<T>::clear()
236
237 Removes all items from the cache. The capacity is unchanged.
238*/
239
240/*! \fn template<typename T> void QContiguousCache<T>::setCapacity(qsizetype size)
241
242 Sets the capacity of the cache to the given \a size. A cache can hold a
243 number of items equal to its capacity. When inserting, appending or prepending
244 items to the cache, if the cache is already full then the item farthest from
245 the added item will be removed.
246
247 If the given \a size is smaller than the current count of items in the cache
248 then only the last \a size items from the cache will remain.
249
250 \sa capacity(), isFull()
251*/
252
253/*! \fn template<typename T> const T &QContiguousCache<T>::at(qsizetype i) const
254
255 Returns the item at index position \a i in the cache. \a i must
256 be a valid index position in the cache (i.e, firstIndex() <= \a i <= lastIndex()).
257
258 The indexes in the cache refer to the number of positions the item is from the
259 first item appended into the cache. That is to say a cache with a capacity of
260 100, that has had 150 items appended will have a valid index range of
261 50 to 149. This allows inserting and retrieving items into the cache based
262 on a theoretical infinite list
263
264 \sa firstIndex(), lastIndex(), insert(), operator[]()
265*/
266
267/*! \fn template<typename T> T &QContiguousCache<T>::operator[](qsizetype i)
268
269 Returns the item at index position \a i as a modifiable reference. If
270 the cache does not contain an item at the given index position \a i
271 then it will first insert an empty item at that position.
272
273 In most cases it is better to use either at() or insert().
274
275 \note This non-const overload of operator[] requires QContiguousCache
276 to make a deep copy. Use at() for read-only access to a non-const
277 QContiguousCache.
278
279 \sa insert(), at()
280*/
281
282/*! \fn template<typename T> const T &QContiguousCache<T>::operator[](qsizetype i) const
283
284 \overload
285
286 Same as at(\a i).
287*/
288
289/*! \fn template<typename T> void QContiguousCache<T>::append(const T &value)
290
291 Inserts \a value at the end of the cache. If the cache is already full
292 the item at the start of the cache will be removed.
293
294 \sa prepend(), insert(), isFull()
295*/
296
297/*! \fn template<typename T> void QContiguousCache<T>::prepend(const T &value)
298
299 Inserts \a value at the start of the cache. If the cache is already full
300 the item at the end of the cache will be removed.
301
302 \sa append(), insert(), isFull()
303*/
304
305/*! \fn template<typename T> void QContiguousCache<T>::insert(qsizetype i, const T &value)
306
307 Inserts the \a value at the index position \a i. If the cache already contains
308 an item at \a i then that value is replaced. If \a i is either one more than
309 lastIndex() or one less than firstIndex() it is the equivalent to an append()
310 or a prepend().
311
312 If the given index \a i is not within the current range of the cache nor adjacent
313 to the bounds of the cache's index range, the cache is first cleared before
314 inserting the item. At this point the cache will have a size of 1. It is
315 worthwhile taking effort to insert items in an order that starts adjacent
316 to the current index range for the cache.
317
318 The range of valid indexes for the QContiguousCache class are from
319 0 to INT_MAX. Inserting outside of this range has undefined behavior.
320
321
322 \sa prepend(), append(), isFull(), firstIndex(), lastIndex()
323*/
324
325/*! \fn template<typename T> bool QContiguousCache<T>::containsIndex(qsizetype i) const
326
327 Returns \c true if the cache's index range includes the given index \a i.
328
329 \sa firstIndex(), lastIndex()
330*/
331
332/*! \fn template<typename T> qsizetype QContiguousCache<T>::firstIndex() const
333
334 Returns the first valid index in the cache. The index will be invalid if the
335 cache is empty.
336
337 \sa capacity(), size(), lastIndex()
338*/
339
340/*! \fn template<typename T> qsizetype QContiguousCache<T>::lastIndex() const
341
342 Returns the last valid index in the cache. The index will be invalid if the cache is empty.
343
344 \sa capacity(), size(), firstIndex()
345*/
346
347
348/*! \fn template<typename T> T &QContiguousCache<T>::first()
349
350 Returns a reference to the first item in the cache. This function
351 assumes that the cache isn't empty.
352
353 \sa last(), isEmpty()
354*/
355
356/*! \fn template<typename T> T &QContiguousCache<T>::last()
357
358 Returns a reference to the last item in the cache. This function
359 assumes that the cache isn't empty.
360
361 \sa first(), isEmpty()
362*/
363
364/*! \fn template<typename T> const T& QContiguousCache<T>::first() const
365
366 \overload
367*/
368
369/*! \fn template<typename T> const T& QContiguousCache<T>::last() const
370
371 \overload
372*/
373
374/*! \fn template<typename T> void QContiguousCache<T>::removeFirst()
375
376 Removes the first item from the cache. This function assumes that
377 the cache isn't empty.
378
379 \sa removeLast()
380*/
381
382/*! \fn template<typename T> void QContiguousCache<T>::removeLast()
383
384 Removes the last item from the cache. This function assumes that
385 the cache isn't empty.
386
387 \sa removeFirst()
388*/
389
390/*! \fn template<typename T> T QContiguousCache<T>::takeFirst()
391
392 Removes the first item in the cache and returns it. This function
393 assumes that the cache isn't empty.
394
395 If you don't use the return value, removeFirst() is more efficient.
396
397 \sa takeLast(), removeFirst()
398*/
399
400/*! \fn template<typename T> T QContiguousCache<T>::takeLast()
401
402 Removes the last item in the cache and returns it. This function
403 assumes that the cache isn't empty.
404
405 If you don't use the return value, removeLast() is more efficient.
406
407 \sa takeFirst(), removeLast()
408*/
409
410/*! \fn template<typename T> void QContiguousCache<T>::normalizeIndexes()
411
412 Moves the first index and last index of the cache
413 such that they point to valid indexes. The function does not modify
414 the contents of the cache or the ordering of elements within the cache.
415
416 It is provided so that index overflows can be corrected when using the
417 cache as a circular buffer.
418
419 \snippet code/src_corelib_tools_qcontiguouscache.cpp 1
420
421 \sa areIndexesValid(), append(), prepend()
422*/
423
424/*! \fn template<typename T> bool QContiguousCache<T>::areIndexesValid() const
425
426 Returns whether the indexes for items stored in the cache are valid.
427 Indexes can become invalid if items are appended after the index position
428 INT_MAX or prepended before the index position 0. This is only expected
429 to occur in very long lived circular buffer style usage of the
430 contiguous cache. Indexes can be made valid again by calling
431 normalizeIndexes().
432
433 \sa normalizeIndexes(), append(), prepend()
434*/
435
436QT_END_NAMESPACE
437

source code of qtbase/src/corelib/tools/qcontiguouscache.cpp