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 ```1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 ``` ``````/**************************************************************************** ** ** Copyright (C) 2014 Digia Plc and/or its subsidiary(-ies). ** Contact: http://www.qt-project.org/legal ** ** This file is part of the QtCore module of the Qt Toolkit. ** ** \$QT_BEGIN_LICENSE:LGPL21\$ ** Commercial License Usage ** Licensees holding valid commercial Qt licenses may use this file in ** accordance with the commercial license agreement provided with the ** Software or, alternatively, in accordance with the terms contained in ** a written agreement between you and Digia. For licensing terms and ** conditions see http://qt.digia.com/licensing. For further information ** use the contact form at http://qt.digia.com/contact-us. ** ** 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 or version 3 as published by the Free ** Software Foundation and appearing in the file LICENSE.LGPLv21 and ** LICENSE.LGPLv3 included in the packaging of this file. Please review the ** following information to ensure the GNU Lesser General Public License ** requirements will be met: https://www.gnu.org/licenses/lgpl.html and ** http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html. ** ** In addition, as a special exception, Digia gives you certain additional ** rights. These rights are described in the Digia Qt LGPL Exception ** version 1.1, included in the file LGPL_EXCEPTION.txt in this package. ** ** \$QT_END_LICENSE\$ ** ****************************************************************************/ /*! \page qtconcurrentfilter.html \title Concurrent Filter and Filter-Reduce \ingroup thread The QtConcurrent::filter(), QtConcurrent::filtered() and QtConcurrent::filteredReduced() functions filter items in a sequence such as a QList or a QVector in parallel. QtConcurrent::filter() modifies a sequence in-place, QtConcurrent::filtered() returns a new sequence containing the filtered content, and QtConcurrent::filteredReduced() returns a single result. These functions are a part of the \l {Qt Concurrent} framework. Each of the above functions have a blocking variant that returns the final result instead of a QFuture. You use them in the same way as the asynchronous variants. \snippet code/src_concurrent_qtconcurrentfilter.cpp 6 Note that the result types above are not QFuture objects, but real result types (in this case, QStringList and QSet). \section1 Concurrent Filter QtConcurrent::filtered() takes an input sequence and a filter function. This filter function is then called for each item in the sequence, and a new sequence containing the filtered values is returned. The filter function must be of the form: \snippet code/src_concurrent_qtconcurrentfilter.cpp 0 T must match the type stored in the sequence. The function returns \c true if the item should be kept, false if it should be discarded. This example shows how to keep strings that are all lower-case from a QStringList: \snippet code/src_concurrent_qtconcurrentfilter.cpp 1 The results of the filter are made available through QFuture. See the QFuture and QFutureWatcher documentation for more information on how to use QFuture in your applications. If you want to modify a sequence in-place, use QtConcurrent::filter(): \snippet code/src_concurrent_qtconcurrentfilter.cpp 2 Since the sequence is modified in place, QtConcurrent::filter() does not return any results via QFuture. However, you can still use QFuture and QFutureWatcher to monitor the status of the filter. \section1 Concurrent Filter-Reduce QtConcurrent::filteredReduced() is similar to QtConcurrent::filtered(), but instead of returing a sequence with the filtered results, the results are combined into a single value using a reduce function. The reduce function must be of the form: \snippet code/src_concurrent_qtconcurrentfilter.cpp 3 T is the type of the final result, U is the type of items being filtered. Note that the return value and return type of the reduce function are not used. Call QtConcurrent::filteredReduced() like this: \snippet code/src_concurrent_qtconcurrentfilter.cpp 4 The reduce function will be called once for each result kept by the filter function, and should merge the \e{intermediate} into the \e{result} variable. QtConcurrent::filteredReduced() guarantees that only one thread will call reduce at a time, so using a mutex to lock the result variable is not necessary. The QtConcurrent::ReduceOptions enum provides a way to control the order in which the reduction is done. \section1 Additional API Features \section2 Using Iterators instead of Sequence Each of the above functions has a variant that takes an iterator range instead of a sequence. You use them in the same way as the sequence variants: \snippet code/src_concurrent_qtconcurrentfilter.cpp 5 \section2 Using Member Functions QtConcurrent::filter(), QtConcurrent::filtered(), and QtConcurrent::filteredReduced() accept pointers to member functions. The member function class type must match the type stored in the sequence: \snippet code/src_concurrent_qtconcurrentfilter.cpp 7 Note that when using QtConcurrent::filteredReduced(), you can mix the use of normal and member functions freely: \snippet code/src_concurrent_qtconcurrentfilter.cpp 8 \section2 Using Function Objects QtConcurrent::filter(), QtConcurrent::filtered(), and QtConcurrent::filteredReduced() accept function objects, which can be used to add state to a function call. The result_type typedef must define the result type of the function call operator: \snippet code/src_concurrent_qtconcurrentfilter.cpp 13 \section2 Using Bound Function Arguments If you want to use a filter function takes more than one argument, you can use std::bind() to transform it onto a function that takes one argument. If C++11 support is not available, \l{http://www.boost.org/libs/bind/bind.html} {boost::bind()} or \l{http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf} {std::tr1::bind()} are suitable replacements. As an example, we use QString::contains(): \snippet code/src_concurrent_qtconcurrentfilter.cpp 9 QString::contains() takes 2 arguments (including the "this" pointer) and can't be used with QtConcurrent::filtered() directly, because QtConcurrent::filtered() expects a function that takes one argument. To use QString::contains() with QtConcurrent::filtered() we have to provide a value for the \e regexp argument: \snippet code/src_concurrent_qtconcurrentfilter.cpp 10 The return value from std::bind() is a function object (functor) with the following signature: \snippet code/src_concurrent_qtconcurrentfilter.cpp 11 This matches what QtConcurrent::filtered() expects, and the complete example becomes: \snippet code/src_concurrent_qtconcurrentfilter.cpp 12 */ /*! \fn QFuture QtConcurrent::filter(Sequence &sequence, FilterFunction filterFunction) Calls \a filterFunction once for each item in \a sequence. If \a filterFunction returns \c true, the item is kept in \a sequence; otherwise, the item is removed from \a sequence. */ /*! \fn QFuture QtConcurrent::filtered(const Sequence &sequence, FilterFunction filterFunction) Calls \a filterFunction once for each item in \a sequence and returns a new Sequence of kept items. If \a filterFunction returns \c true, a copy of the item is put in the new Sequence. Otherwise, the item will \e not appear in the new Sequence. */ /*! \fn QFuture QtConcurrent::filtered(ConstIterator begin, ConstIterator end, FilterFunction filterFunction) Calls \a filterFunction once for each item from \a begin to \a end and returns a new Sequence of kept items. If \a filterFunction returns \c true, a copy of the item is put in the new Sequence. Otherwise, the item will \e not appear in the new Sequence. */ /*! \fn QFuture QtConcurrent::filteredReduced(const Sequence &sequence, FilterFunction filterFunction, ReduceFunction reduceFunction, QtConcurrent::ReduceOptions reduceOptions) Calls \a filterFunction once for each item in \a sequence. If \a filterFunction returns \c true for an item, that item is then passed to \a reduceFunction. In other words, the return value is the result of \a reduceFunction for each item where \a filterFunction returns \c true. Note that while \a filterFunction is called concurrently, only one thread at a time will call \a reduceFunction. The order in which \a reduceFunction is called is undefined if \a reduceOptions is QtConcurrent::UnorderedReduce. If \a reduceOptions is QtConcurrent::OrderedReduce, \a reduceFunction is called in the order of the original sequence. */ /*! \fn QFuture QtConcurrent::filteredReduced(ConstIterator begin, ConstIterator end, FilterFunction filterFunction, ReduceFunction reduceFunction, QtConcurrent::ReduceOptions reduceOptions) Calls \a filterFunction once for each item from \a begin to \a end. If \a filterFunction returns \c true for an item, that item is then passed to \a reduceFunction. In other words, the return value is the result of \a reduceFunction for each item where \a filterFunction returns \c true. Note that while \a filterFunction is called concurrently, only one thread at a time will call \a reduceFunction. The order in which \a reduceFunction is called is undefined if \a reduceOptions is QtConcurrent::UnorderedReduce. If \a reduceOptions is QtConcurrent::OrderedReduce, the \a reduceFunction is called in the order of the original sequence. */ /*! \fn void QtConcurrent::blockingFilter(Sequence &sequence, FilterFunction filterFunction) Calls \a filterFunction once for each item in \a sequence. If \a filterFunction returns \c true, the item is kept in \a sequence; otherwise, the item is removed from \a sequence. \note This function will block until all items in the sequence have been processed. */ /*! \fn Sequence QtConcurrent::blockingFiltered(const Sequence &sequence, FilterFunction filterFunction) Calls \a filterFunction once for each item in \a sequence and returns a new Sequence of kept items. If \a filterFunction returns \c true, a copy of the item is put in the new Sequence. Otherwise, the item will \e not appear in the new Sequence. \note This function will block until all items in the sequence have been processed. \sa filtered() */ /*! \fn Sequence QtConcurrent::blockingFiltered(ConstIterator begin, ConstIterator end, FilterFunction filterFunction) Calls \a filterFunction once for each item from \a begin to \a end and returns a new Sequence of kept items. If \a filterFunction returns \c true, a copy of the item is put in the new Sequence. Otherwise, the item will \e not appear in the new Sequence. \note This function will block until the iterator reaches the end of the sequence being processed. \sa filtered() */ /*! \fn T QtConcurrent::blockingFilteredReduced(const Sequence &sequence, FilterFunction filterFunction, ReduceFunction reduceFunction, QtConcurrent::ReduceOptions reduceOptions) Calls \a filterFunction once for each item in \a sequence. If \a filterFunction returns \c true for an item, that item is then passed to \a reduceFunction. In other words, the return value is the result of \a reduceFunction for each item where \a filterFunction returns \c true. Note that while \a filterFunction is called concurrently, only one thread at a time will call \a reduceFunction. The order in which \a reduceFunction is called is undefined if \a reduceOptions is QtConcurrent::UnorderedReduce. If \a reduceOptions is QtConcurrent::OrderedReduce, \a reduceFunction is called in the order of the original sequence. \note This function will block until all items in the sequence have been processed. \sa filteredReduced() */ /*! \fn T QtConcurrent::blockingFilteredReduced(ConstIterator begin, ConstIterator end, FilterFunction filterFunction, ReduceFunction reduceFunction, QtConcurrent::ReduceOptions reduceOptions) Calls \a filterFunction once for each item from \a begin to \a end. If \a filterFunction returns \c true for an item, that item is then passed to \a reduceFunction. In other words, the return value is the result of \a reduceFunction for each item where \a filterFunction returns \c true. Note that while \a filterFunction is called concurrently, only one thread at a time will call \a reduceFunction. The order in which \a reduceFunction is called is undefined if \a reduceOptions is QtConcurrent::UnorderedReduce. If \a reduceOptions is QtConcurrent::OrderedReduce, the \a reduceFunction is called in the order of the original sequence. \note This function will block until the iterator reaches the end of the sequence being processed. \sa filteredReduced() */ ``````