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  • Qt多线程-QtConcurrent并行运算高级API

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    本文标题：Qt多线程-QtConcurrent并行运算高级API     本文地址：http://techieliang.com/2017/12/608/

    1. 介绍

    Qt除了提供基本的QThread实现多线程，并提供QThreadPool实现线程池以外，还提供了QtConcurrent模块用于并行计算。

    使用此类需要在pro文件增加QT += concurrent

    QtConcurrent命名空间帮助文档，API介绍帮助

    1.1. API

    1. void blockingFilter(Sequence &sequence, FilterFunction filterFunction)
    2. Sequence blockingFiltered(const Sequence &sequence, FilterFunction filterFunction)
    3. Sequence blockingFiltered(ConstIterator begin, ConstIterator end, FilterFunction filterFunction)
    4. T blockingFilteredReduced(const Sequence &sequence, FilterFunction filterFunction, ReduceFunction reduceFunction, QtConcurrent::ReduceOptions reduceOptions = UnorderedReduce | SequentialReduce)
    5. T blockingFilteredReduced(ConstIterator begin, ConstIterator end, FilterFunction filterFunction, ReduceFunction reduceFunction, QtConcurrent::ReduceOptions reduceOptions = UnorderedReduce | SequentialReduce)
    6. void blockingMap(Sequence &sequence, MapFunction function)
    7. void blockingMap(Iterator begin, Iterator end, MapFunction function)
    8. T blockingMapped(const Sequence &sequence, MapFunction function)
    9. T blockingMapped(ConstIterator begin, ConstIterator end, MapFunction function)
    10. T blockingMappedReduced(const Sequence &sequence, MapFunction mapFunction, ReduceFunction reduceFunction, QtConcurrent::ReduceOptions reduceOptions = UnorderedReduce | SequentialReduce)
    11. T blockingMappedReduced(ConstIterator begin, ConstIterator end, MapFunction mapFunction, ReduceFunction reduceFunction, QtConcurrent::ReduceOptions reduceOptions = UnorderedReduce | SequentialReduce)
    12. QFuture<void> filter(Sequence &sequence, FilterFunction filterFunction)
    13. QFuture<T> filtered(const Sequence &sequence, FilterFunction filterFunction)
    14. QFuture<T> filtered(ConstIterator begin, ConstIterator end, FilterFunction filterFunction)
    15. QFuture<T> filteredReduced(const Sequence &sequence, FilterFunction filterFunction, ReduceFunction reduceFunction, QtConcurrent::ReduceOptions reduceOptions = UnorderedReduce | SequentialReduce)
    16. QFuture<T> filteredReduced(ConstIterator begin, ConstIterator end, FilterFunction filterFunction, ReduceFunction reduceFunction, QtConcurrent::ReduceOptions reduceOptions = UnorderedReduce | SequentialReduce)
    17. QFuture<void> map(Sequence &sequence, MapFunction function)
    18. QFuture<void> map(Iterator begin, Iterator end, MapFunction function)
    19. QFuture<T> mapped(const Sequence &sequence, MapFunction function)
    20. QFuture<T> mapped(ConstIterator begin, ConstIterator end, MapFunction function)
    21. QFuture<T> mappedReduced(const Sequence &sequence, MapFunction mapFunction, ReduceFunction reduceFunction, QtConcurrent::ReduceOptions reduceOptions = UnorderedReduce | SequentialReduce)
    22. QFuture<T> mappedReduced(ConstIterator begin, ConstIterator end, MapFunction mapFunction, ReduceFunction reduceFunction, QtConcurrent::ReduceOptions reduceOptions = UnorderedReduce | SequentialReduce)
    23. QFuture<T> run(Function function, ...)
    24. QFuture<T> run(QThreadPool *pool, Function function, ...)

    很多都是重载的，主要函数如下：

    • Concurrent Map and Map-Reduce
      • QtConcurrent::map() applies a function to every item in a container, modifying the items in-place.
      • –这个函数会将作为参数传入的函数应用到容器中的每一项，对这些项进行直接修改，会修改传入变量内容。
      • QtConcurrent::mapped() is like map(), except that it returns a new container with the modifications.
      • –功能类似于map()，只不过它不是直接修改原始容器，而是将修改后的元素放到一个新的容器中并作为返回值返回。
      • QtConcurrent::mappedReduced() is like mapped(), except that the modified results are reduced or folded into a single result.
      • –功能类似于mapped()，首先执行mapped的操作，然后传入一个Reduce函数进行简化，最终返回唯一一个元素，此操作不会修改原始容器。
    • Concurrent Filter and Filter-Reduce
      • QtConcurrent::filter() removes all items from a container based on the result of a filter function.
      • –从容器中删除那些满足某个过来条件的项。
      • QtConcurrent::filtered() is like filter(), except that it returns a new container with the filtered results.
      • –功能类似于filter()，只不过它会返回一个包含剩余元素的容器。
      • QtConcurrent::filteredReduced() is like filtered(), except that the filtered results are reduced or folded into a single result.
      • –功能类似于filtered()，后续进行reduce操作。
    • Concurrent Run
      • QtConcurrent::run() runs a function in another thread.
      • –用另一个进程运行一个函数
    • QFuture represents the result of an asynchronous computation.
    • — 获取一步计算结果
    • QFutureIterator allows iterating through results available via QFuture.
    • –通过使用QFuture允许遍历结果
    • QFutureWatcher allows monitoring a QFuture using signals-and-slots.
    • — 利用信号槽监视QFuture
    • QFutureSynchronizer is a convenience class that automatically synchronizes several QFutures.
    • –自动同步多个futures

    2. QtConcurrent::map

    map的范例：http://doc.qt.io/qt-5/qtconcurrent-map-example.html

    map详细介绍：http://doc.qt.io/qt-5/qtconcurrentmap.html

    1. #include <QCoreApplication>
    2. #include <QtConcurrent>
    3. #include <QVector>
    4. #include <QDebug>
    5. #include <QFuture>
    6. void MapFunction(int& num) {
    7. num += 1;
    8. }
    9. int mappedReducedFunction(const int& num) {
    10. return num + 1;
    11. }
    12. void ReduceFunction(int& result, const int& item) {
    13. int t_r = result;
    14. result = item > result ? item : result;
    15. qDebug()<<t_r<<result<<item;
    16. }
    17. int main(int argc, char *argv[]) {
    18. QCoreApplication a(argc, argv);
    19. QVector<int> testVactor;
    20. for(int i = 1; i <= 3; i++) {
    21. testVactor.push_back(i);
    22. }
    23. for(int i = 1; i <= 3; i++) {
    24. testVactor.push_back(10-i);
    25. }
    26. qDebug() << "start m:" << testVactor;
    27. QFuture<void> f = QtConcurrent::map(testVactor, MapFunction);
    28. f.waitForFinished();
    29. qDebug() << "map result:" << testVactor;//map直接修改源数据
    30. QFuture<int> r = QtConcurrent::mappedReduced(testVactor, mappedReducedFunction, ReduceFunction);
    31. qDebug() << "mappedReduced result:" << r.result();
    32. return 0;
    33. }

    注意几个函数的声明形式，不可有差距。结果

    1. start m: QVector(1, 2, 3, 9, 8, 7)
    2. map result: QVector(2, 3, 4, 10, 9, 8)
    3. 0 3 3
    4. 3 4 4
    5. 4 5 5
    6. 5 11 11
    7. 11 11 10
    8. 11 11 9
    9. mappedReduced result: 11

    结果示意很明显，reduced最终表留的是等于函数result参数值的项

    3. QtConcurrent::filter

    filter详细介绍：http://doc.qt.io/qt-5/qtconcurrentfilter.html

    1. #include <QCoreApplication>
    2. #include <QtConcurrent>
    3. #include <QList>
    4. #include <QDebug>
    5. #include <QFuture>
    6. bool filterFunction(const int& num) {
    7. return (num > 5);
    8. }
    9. void ReduceFunction(int& result, const int& item) {
    10. int t_r = result;
    11. result = item > result ? item : result;
    12. qDebug()<<t_r<<result<<item;
    13. }
    14. int main(int argc, char *argv[]) {
    15. QCoreApplication a(argc, argv);
    16. QList<int> testVactor;
    17. for(int i = 1; i <= 3; i++) {
    18. testVactor.push_back(i);
    19. }
    20. for(int i = 1; i <= 3; i++) {
    21. testVactor.push_back(10-i);
    22. }
    23. qDebug() << "start m:" << testVactor;
    24. QFuture<void> f = QtConcurrent::filter(testVactor, filterFunction);
    25. f.waitForFinished();
    26. qDebug() << "map result:" << testVactor;//map直接修改源数据
    27. QFuture<int> r = QtConcurrent::filteredReduced(testVactor, filterFunction, ReduceFunction);
    28. qDebug() << "mappedReduced result:" << r.result();
    29. return 0;
    30. }

    注意几个函数的声明形式，不可有差距。filter函数要返回bool类型，用于判断是否过滤此元素

    结果：

    1. start m: (1, 2, 3, 9, 8, 7)
    2. map result: (9, 8, 7)
    3. 0 9 9
    4. 9 9 8
    5. 9 9 7
    6. mappedReduced result: 9

    4. QtConcurrent::run

    感觉run用起来很舒服，因为他没有对运行函数头做限制，可以是任意数量的任意类型参数。

    run的详细帮助：http://doc.qt.io/qt-5/qtconcurrentrun.html，也可以看看本机的qtconcurrentrun.h文件，可以看到里面有很多的run的重载函数

    下面给出最基本的使用

    1. #include <QCoreApplication>
    2. #include <QtConcurrent>
    3. #include <QList>
    4. #include <QDebug>
    5. #include <QThread>
    6. void function(const QList<int>& param1, const int& param2, Qt::HANDLE main_id) {
    7. qDebug()<<"function param:"<<param1<<param2<<main_id;
    8. qDebug()<<"function thread id:" <<QThread::currentThreadId();
    9. }
    10. int main(int argc, char *argv[]) {
    11. QCoreApplication a(argc, argv);
    12. QList<int> testVactor;
    13. for(int i = 1; i <= 3; i++) {
    14. testVactor.push_back(i);
    15. }
    16. qDebug() << "main thread id:" << QThread::currentThreadId();
    17. QFuture<void> f = QtConcurrent::run(function,testVactor,666,QThread::currentThreadId());
    18. f.waitForFinished();//要等待，否则线程没运行完程序结束会出错
    19. return 0;
    20. }

    结果

    1. main thread id: 0x2a10
    2. function param: (1, 2, 3) 666 0x2a10
    3. function thread id: 0x2344

    4.1. 其他使用方式-指定线程池

    有时候希望运行的函数在全局线程池或者局部线程池运行，而不是有qt托管处理，可以进行如下方式调用：

    1. extern void aFunction();
    2. QThreadPool pool;
    3. QFuture<void> future = QtConcurrent::run(&pool, aFunction);

    5. 阻塞QtConcurrent

    上述所有函数都是非阻塞的，所以在return 0前都有waitForFinished，qt同样提供了阻塞函数

    见最开始API帮助介绍连接，可以看到相关接口

    1. void blockingFilter(Sequence &sequence, FilterFunction filterFunction)
    2. Sequence blockingFiltered(const Sequence &sequence, FilterFunction filterFunction)
    3. Sequence blockingFiltered(ConstIterator begin, ConstIterator end, FilterFunction filterFunction)
    4. T blockingFilteredReduced(const Sequence &sequence, FilterFunction filterFunction, ReduceFunction reduceFunction, QtConcurrent::ReduceOptions reduceOptions = UnorderedReduce | SequentialReduce)
    5. T blockingFilteredReduced(ConstIterator begin, ConstIterator end, FilterFunction filterFunction, ReduceFunction reduceFunction, QtConcurrent::ReduceOptions reduceOptions = UnorderedReduce | SequentialReduce)
    6. void blockingMap(Sequence &sequence, MapFunction function)
    7. void blockingMap(Iterator begin, Iterator end, MapFunction function)
    8. T blockingMapped(const Sequence &sequence, MapFunction function)
    9. T blockingMapped(ConstIterator begin, ConstIterator end, MapFunction function)
    10. T blockingMappedReduced(const Sequence &sequence, MapFunction mapFunction, ReduceFunction reduceFunction, QtConcurrent::ReduceOptions reduceOptions = UnorderedReduce | SequentialReduce)
    11. T blockingMappedReduced(ConstIterator begin, ConstIterator end, MapFunction mapFunction, ReduceFunction reduceFunction, QtConcurrent::ReduceOptions reduceOptions = UnorderedReduce | SequentialReduce)

    可以看到对应函数的介绍都有：

    Note: This function will block until all items in the sequence have been processed.

    使用方式近似，不提供示例了。

    转载请以链接形式标明本文标题和地址：Techie亮博客 » Qt多线程-QtConcurrent并行运算高级API
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  • 原文地址：https://www.cnblogs.com/techiel/p/8018384.html
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