- Qt 5.5
- Qt Concurrent
- QtConcurrent Word Count Example
- main.cpp Example File
- Qt 5.5.1 Reference Documentation

# main.cpp Example File

wordcount/main.cpp

    /****************************************************************************
    **
    ** Copyright (C) 2015 The Qt Company Ltd.
    ** Contact: http://www.qt.io/licensing/
    **
    ** This file is part of the examples of the Qt Toolkit.
    **
    ** $QT_BEGIN_LICENSE:BSD$
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    **     from this software without specific prior written permission.
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    #include <QList>
    #include <QMap>
    #include <QTextStream>
    #include <QString>
    #include <QStringList>
    #include <QDir>
    #include <QTime>
    #include <QApplication>
    #include <QDebug>

    #include <qtconcurrentmap.h>

    using namespace QtConcurrent;

    /*
        Utility function that recursivily searches for files.
    */
    QStringList findFiles(const QString &startDir, QStringList filters)
    {
        QStringList names;
        QDir dir(startDir);

        foreach (QString file, dir.entryList(filters, QDir::Files))
            names += startDir + "/" + file;

        foreach (QString subdir, dir.entryList(QDir::AllDirs | QDir::NoDotAndDotDot))
            names += findFiles(startDir + "/" + subdir, filters);
        return names;
    }

    typedef QMap<QString, int> WordCount;

    /*
        Single threaded word counter function.
    */
    WordCount singleThreadedWordCount(QStringList files)
    {
        WordCount wordCount;
        foreach (QString file, files) {
            QFile f(file);
            f.open(QIODevice::ReadOnly);
            QTextStream textStream(&f);
            while (textStream.atEnd() == false)
                foreach(QString word, textStream.readLine().split(" "))
                    wordCount[word] += 1;

        }
        return wordCount;
    }

    // countWords counts the words in a single file. This function is
    // called in parallel by several threads and must be thread
    // safe.
    WordCount countWords(const QString &file)
    {
        QFile f(file);
        f.open(QIODevice::ReadOnly);
        QTextStream textStream(&f);
        WordCount wordCount;

        while (textStream.atEnd() == false)
            foreach (QString word, textStream.readLine().split(" "))
                wordCount[word] += 1;

        return wordCount;
    }

    // reduce adds the results from map to the final
    // result. This functor will only be called by one thread
    // at a time.
    void reduce(WordCount &result, const WordCount &w)
    {
        QMapIterator<QString, int> i(w);
        while (i.hasNext()) {
            i.next();
            result[i.key()] += i.value();
        }
    }

    int main(int argc, char** argv)
    {
        QApplication app(argc, argv);
        qDebug() << "finding files...";
        QStringList files = findFiles("../../", QStringList() << "*.cpp" << "*.h");
        qDebug() << files.count() << "files";

        qDebug() << "warmup";
        {
            QTime time;
            time.start();
            WordCount total = singleThreadedWordCount(files);
        }

        qDebug() << "warmup done";

        int singleThreadTime = 0;
        {
            QTime time;
            time.start();
            WordCount total = singleThreadedWordCount(files);
            singleThreadTime = time.elapsed();
            qDebug() << "single thread" << singleThreadTime;
        }

        int mapReduceTime = 0;
        {
            QTime time;
            time.start();
            WordCount total = mappedReduced(files, countWords, reduce);
            mapReduceTime = time.elapsed();
            qDebug() << "MapReduce" << mapReduceTime;
        }
        qDebug() << "MapReduce speedup x" << ((double)singleThreadTime - (double)mapReduceTime) / (double)mapReduceTime + 1;
    }