main.cpp Example File

 /****************************************************************************
 **
 ** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
 ** All rights reserved.
 ** Contact: Nokia Corporation (qt-info@nokia.com)
 **
 ** This file is part of the examples of the Qt Toolkit.
 **
 ** $QT_BEGIN_LICENSE:BSD$
 ** You may use this file under the terms of the BSD license as follows:
 **
 ** "Redistribution and use in source and binary forms, with or without
 ** modification, are permitted provided that the following conditions are
 ** met:
 **   * Redistributions of source code must retain the above copyright
 **     notice, this list of conditions and the following disclaimer.
 **   * Redistributions in binary form must reproduce the above copyright
 **     notice, this list of conditions and the following disclaimer in
 **     the documentation and/or other materials provided with the
 **     distribution.
 **   * Neither the name of Nokia Corporation and its Subsidiary(-ies) nor
 **     the names of its contributors may be used to endorse or promote
 **     products derived from this software without specific prior written
 **     permission.
 **
 ** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 ** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 ** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 ** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 ** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 ** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 ** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 ** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 ** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 ** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
 ** $QT_END_LICENSE$
 **
 ****************************************************************************/

 #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...";
 #ifdef Q_WS_MAEMO_5
     QStringList files = findFiles("/usr/", QStringList() << "*.sh");
 #else
     QStringList files = findFiles("../../", QStringList() << "*.cpp" << "*.h");
 #endif
     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

 #include <QLabel>

 int main(int argc, char *argv[])
 {
     QApplication app(argc, argv);
     QString text("Qt Concurrent is not yet supported on this platform");

     QLabel *label = new QLabel(text);
     label->setWordWrap(true);

 #if defined(Q_WS_S60) || defined(Q_WS_MAEMO_5)
     label->showMaximized();
 #else
     label->show();
 #endif
     qDebug() << text;

     app.exec();
 }

 #endif