main.cpp Example File

wordcount/main.cpp
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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; }

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