Qt Reference Documentation

# main.cpp Example File

qtconcurrent/wordcount/main.cpp

     /****************************************************************************
     **
     ** 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
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     **   * Redistributions of source code must retain the above copyright
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     **     notice, this list of conditions and the following disclaimer in
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     **     distribution.
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     **     the names of its contributors may be used to endorse or promote
     **     products derived from this software without specific prior written
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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>

     #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