main.cpp Example File

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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, const QStringList &filters)
  {
      QStringList names;
      QDir dir(startDir);

      const auto files = dir.entryList(filters, QDir::Files);
      for (const QString &file : files)
          names += startDir + '/' + file;

      const auto subdirs =  dir.entryList(QDir::AllDirs | QDir::NoDotAndDotDot);
      for (const QString &subdir : subdirs)
          names += findFiles(startDir + '/' + subdir, filters);
      return names;
  }

  typedef QMap<QString, int> WordCount;

  /*
      Single threaded word counter function.
  */
  WordCount singleThreadedWordCount(const QStringList &files)
  {
      WordCount wordCount;
      for (const QString &file : files) {
          QFile f(file);
          f.open(QIODevice::ReadOnly);
          QTextStream textStream(&f);
          while (!textStream.atEnd()) {
              const auto words =  textStream.readLine().split(' ');
              for (const QString &word : words)
                  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()) {
          const auto words =  textStream.readLine().split(' ');
          for (const QString &word : words)
              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";
      {
          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;
  }