main.cpp Example File
qtconcurrent/wordcount/main.cpp

 /****************************************************************************
 **
 ** Copyright (C) 2007-2008 Nokia Corporation and/or its subsidiary(-ies). All rights reserved.
 **
 ** This file is part of the documentation of the Qt Toolkit.
 **
 ** Licensees holding a valid Qt License Agreement may use this file in
 ** accordance with the rights, responsibilities and obligations
 ** contained therein.  Please consult your licensing agreement or
 ** contact qt-sales@nokia.com if any conditions of this licensing
 ** agreement are not clear to you.
 **
 ** Further information about Qt licensing is available at:
 ** http://trolltech.com/products/appdev/licensing.
 **
 ** This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
 ** WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 **
 ****************************************************************************/

 #include <QList>
 #include <QMap>
 #include <QTextStream>
 #include <QString>
 #include <QStringList>
 #include <QDir>
 #include <QTime>
 #include <QApplication>
 #include <QDebug>

 #include <qtconcurrentmap.h>

 #ifndef QT_NO_CONCURRENT

 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;
 }

 #else

 int main()
 {
         qDebug() << "Qt Concurrent is not yet supported on this platform";
 }

 #endif