Can I search for files via QtConcurrent?

[RazrFalcon]

I need to find files on my HDD (recursively).
But it takes a long of time and GUI freezes.
I try to solve it via QtConcurrent:
@void MainWindow::on_buttonSearch_clicked()
{
QFutureWatcher<QFileInfoList> watcher;
connect(&watcher, SIGNAL(finished()), this, SLOT(loadFinished()));
future = QtConcurrent::run(&MainWindow::searchForFiles, lineEditInDir->text()); // in .h QFuture<QFileInfoList> future;
watcher.setFuture(future);
}

QFileInfoList MainWindow::searchForFiles(const QString &startDir)
{
QDir dir(startDir);
QFileInfoList list;
foreach (QString file, dir.entryList(QStringList("*.svg"), QDir::Files))
list += QFileInfo(startDir+"/"+file);
foreach (QString subdir, dir.entryList(QDir::AllDirs | QDir::NoDotAndDotDot))
list += searchForFiles(startDir+"/"+subdir);
return list;
}

void MainWindow::loadFinished()
{
fileList = future.result();
qDebug()<<fileList.count();
}@

All works fine, I think, but I can't cancel it. future.cancel() didn't work, because I use QtConcurrent::run().
And i don't know how to put files search into QtConcurrent::mapped(), which can be canceled.

[andre]

I think it would be useless to use QtConcurrent for this. QtConcurrent is suitable for problems that are are easy to parallelize. Searching your HDD will have I/O as the bottleneck, so using multiple threads to do that is not efficient. The threads will end up waiting for each other.

So, I would use either a QObject derived worker that you move to a vanilla [[doc:QThread]], or a [[doc:QRunnable]] subclass in conjunction with [[doc:QThreadPool]]. Because you seem to need cancel capabilities, I think the QThread route would be easiest.

[goetz]

Using QtConcurrent can even worse the situation as OS caches might get flushed once the next thread is running and the data needs to be re-read if the first thread is active again.