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50
51#include <QList>
52#include <QMap>
53#include <QTextStream>
54#include <QString>
55#include <QStringList>
56#include <QDir>
57#include <QElapsedTimer>
58#include <QApplication>
59#include <QDebug>
60
61#include <qtconcurrentmap.h>
62
63using namespace QtConcurrent;
64
65/*
66 Utility function that recursivily searches for files.
67*/
68QStringList findFiles(const QString &startDir, const QStringList &filters)
69{
70 QStringList names;
71 QDir dir(startDir);
72
73 const auto files = dir.entryList(nameFilters: filters, filters: QDir::Files);
74 for (const QString &file : files)
75 names += startDir + '/' + file;
76
77 const auto subdirs = dir.entryList(filters: QDir::AllDirs | QDir::NoDotAndDotDot);
78 for (const QString &subdir : subdirs)
79 names += findFiles(startDir: startDir + '/' + subdir, filters);
80 return names;
81}
82
83typedef QMap<QString, int> WordCount;
84
85/*
86 Single threaded word counter function.
87*/
88WordCount singleThreadedWordCount(const QStringList &files)
89{
90 WordCount wordCount;
91 for (const QString &file : files) {
92 QFile f(file);
93 f.open(flags: QIODevice::ReadOnly);
94 QTextStream textStream(&f);
95 while (!textStream.atEnd()) {
96 const auto words = textStream.readLine().split(sep: ' ');
97 for (const QString &word : words)
98 wordCount[word] += 1;
99 }
100 }
101 return wordCount;
102}
103
104
105// countWords counts the words in a single file. This function is
106// called in parallel by several threads and must be thread
107// safe.
108WordCount countWords(const QString &file)
109{
110 QFile f(file);
111 f.open(flags: QIODevice::ReadOnly);
112 QTextStream textStream(&f);
113 WordCount wordCount;
114
115 while (!textStream.atEnd()) {
116 const auto words = textStream.readLine().split(sep: ' ');
117 for (const QString &word : words)
118 wordCount[word] += 1;
119 }
120
121 return wordCount;
122}
123
124// reduce adds the results from map to the final
125// result. This functor will only be called by one thread
126// at a time.
127void reduce(WordCount &result, const WordCount &w)
128{
129 for (auto i = w.begin(), end = w.end(); i != end; ++i)
130 result[i.key()] += i.value();
131}
132
133int main(int argc, char** argv)
134{
135 QApplication app(argc, argv);
136 qDebug() << "finding files...";
137 QStringList files = findFiles(startDir: "../../", filters: QStringList() << "*.cpp" << "*.h");
138 qDebug() << files.count() << "files";
139
140 qDebug() << "warmup";
141 {
142 WordCount total = singleThreadedWordCount(files);
143 }
144
145 qDebug() << "warmup done";
146
147 int singleThreadTime = 0;
148 {
149 QElapsedTimer timer;
150 timer.start();
151 WordCount total = singleThreadedWordCount(files);
152 singleThreadTime = timer.elapsed();
153 qDebug() << "single thread" << singleThreadTime;
154 }
155
156 int mapReduceTime = 0;
157 {
158 QElapsedTimer timer;
159 timer.start();
160 WordCount total = mappedReduced(sequence: files, map: countWords, reduce);
161 mapReduceTime = timer.elapsed();
162 qDebug() << "MapReduce" << mapReduceTime;
163 }
164 qDebug() << "MapReduce speedup x" << ((double)singleThreadTime - (double)mapReduceTime) / (double)mapReduceTime + 1;
165}
166

source code of qtbase/examples/qtconcurrent/wordcount/main.cpp