Qt多線程-QtConcurrent並行運算高級API

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本文標題：Qt多線程-QtConcurrent並行運算高級API     本文地址： http://techieliang.com/2017/12/608/

文章目錄

• 1. 介紹
•  1.1. API
• 2. QtConcurrent::map
• 3. QtConcurrent::filter
• 4. QtConcurrent::run
•  4.1. 其他使用方式-指定線程池
• 5. 阻塞QtConcurrent

1. 介紹

Qt除了提供基本的QThread實現多線程，並提供QThreadPool實現線程池以外，還提供了QtConcurrent模塊用於並行計算。

使用此類需要在pro文件增加QT += concurrent

QtConcurrent命名空間幫助文檔，API介紹幫助

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, ...)

很多都是重載的，主要函數如下：

• Concurrent Map and Map-Reduce
  • QtConcurrent::map() applies a function to every item in a container, modifying the items in-place.
  • –這個函數會將作為參數傳入的函數應用到容器中的每一項，對這些項進行直接修改，會修改傳入變量內容。
  • QtConcurrent::mapped() is like map(), except that it returns a new container with the modifications.
  • –功能類似於map()，只不過它不是直接修改原始容器，而是將修改后的元素放到一個新的容器中並作為返回值返回。
  • QtConcurrent::mappedReduced() is like mapped(), except that the modified results are reduced or folded into a single result.
  • –功能類似於mapped()，首先執行mapped的操作，然后傳入一個Reduce函數進行簡化，最終返回唯一一個元素，此操作不會修改原始容器。

• Concurrent Filter and Filter-Reduce
  • QtConcurrent::filter() removes all items from a container based on the result of a filter function.
  • –從容器中刪除那些滿足某個過來條件的項。
  • QtConcurrent::filtered() is like filter(), except that it returns a new container with the filtered results.
  • –功能類似於filter()，只不過它會返回一個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.
  • –功能類似於filtered()，后續進行reduce操作。
• Concurrent Run
  • QtConcurrent::run() runs a function in another thread.
  • –用另一個進程運行一個函數
• QFuture represents the result of an asynchronous computation.
• — 獲取一步計算結果
• QFutureIterator allows iterating through results available via QFuture.
• –通過使用QFuture允許遍歷結果
• QFutureWatcher allows monitoring a QFuture using signals-and-slots.
• — 利用信號槽監視QFuture
• QFutureSynchronizer is a convenience class that automatically synchronizes several QFutures.
• –自動同步多個futures

2. QtConcurrent::map

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

map詳細介紹：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直接修改源數據
30. QFuture<int> r = QtConcurrent::mappedReduced(testVactor, mappedReducedFunction, ReduceFunction);
31. qDebug() << "mappedReduced result:" << r.result();
32. return 0;
33. }

注意幾個函數的聲明形式，不可有差距。結果

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

結果示意很明顯，reduced最終表留的是等於函數result參數值的項

3. QtConcurrent::filter

filter詳細介紹：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直接修改源數據
27. QFuture<int> r = QtConcurrent::filteredReduced(testVactor, filterFunction, ReduceFunction);
28. qDebug() << "mappedReduced result:" << r.result();
29. return 0;
30. }

注意幾個函數的聲明形式，不可有差距。filter函數要返回bool類型，用於判斷是否過濾此元素

結果：

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

感覺run用起來很舒服，因為他沒有對運行函數頭做限制，可以是任意數量的任意類型參數。

run的詳細幫助：http://doc.qt.io/qt-5/qtconcurrentrun.html，也可以看看本機的qtconcurrentrun.h文件，可以看到里面有很多的run的重載函數

下面給出最基本的使用

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，否則線程沒運行完程序結束會出錯
19. return 0;
20. }

結果

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-指定線程池

有時候希望運行的函數在全局線程池或者局部線程池運行，而不是有qt托管處理，可以進行如下方式調用：

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

5. 阻塞QtConcurrent

上述所有函數都是非阻塞的，所以在return 0前都有waitForFinished，qt同樣提供了阻塞函數

見最開始API幫助介紹連接，可以看到相關接口

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)

可以看到對應函數的介紹都有：

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。

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