Program freeze when try to get MD5 of files

saeid0034

Hi im using this code for generate MD5 of files in QT

QString Md5_gen(QString const &s)
{
    QString pakchunk_Md5;
    QCryptographicHash crypto(QCryptographicHash::Md5);
    QFile pakchunk(QDir::currentPath() + s);
    if (pakchunk.open(QFile::ReadOnly))
    {
        while(!pakchunk.atEnd()){
        crypto.addData(pakchunk.read(8192));
        }
    } else
    {
        qDebug() << "Can't open file.";
        pakchunk_Md5 = "nofile";
        return pakchunk_Md5
    }
    pakchunk_Md5 = crypto.result().toHex();
    return pakchunk_Md5;
}

its work well, but problem is when program start to generate MD5 of files, gui Freeze until all MD5 generated.
how can i fix this problem?

SGaist

Hi,

One way is to offload the work using QtConcurrent.

sierdzio

@saeid0034 said in Program freeze when try to get MD5 of files:

crypto.addData(pakchunk.read(8192));

Please note that you are also wasting RAM using this approach. Use the QIODevice overload to get the same result - without a loop and with less memory used.

sierdzio

Also, you probably should add return pakchunk_Md5; in your else block.

saeid0034

@sierdzio thanks yes you are right, i edited my code
and about using QIODevice, do you have any example for it?

saeid0034

@SGaist thanks for reply, do you have any example close to my problem?

SGaist

Did you check the examples from the documentation ?

saeid0034

@SGaist i need to use what function of QtConcurrent?

saeid0034

i use this code (i dont know if its right or not)

QString loc40 = "/file/test.pak";
    QFuture<QString> future40 = QtConcurrent::run(QThreadPool::globalInstance(), Md5_gen, loc40);
    QString pakchunk40 = future40.result();

but program freeze again

SGaist

As explained in the result documentation, it will block if the computation is not done. Use QFutureWatcher with signals and slots to properly make things asynchronous.

saeid0034

@SGaist The computation is done
Because the outputs are correct after the program exits From freeze, the only problem is program freeze, no matter how i try, and i sure problem coming from MD5 Generation

saeid0034

i test Q In my code

    QFutureWatcher<void>* watcher = new QFutureWatcher<void>();
    connect(watcher, SIGNAL(finished()), this, SLOT(Md5_gen()));
    watcher->setFuture(future33);

It is wrong or ok?
i dont know how add my function to slot, i just put my md5 function name on it

saeid0034

here is my full code for now

QString Md5_gen(QString const &s)
{
    QString pakchunk_Md5;
    QCryptographicHash crypto(QCryptographicHash::Md5);
    QFile pakchunk(QDir::currentPath() + s);
    if (pakchunk.open(QIODevice::ReadOnly))
    {
        while(!pakchunk.atEnd()){
        crypto.addData(pakchunk.read(8192));
        }
    } else
    {
        qDebug() << "Can't open file.";
        pakchunk_Md5 = "nofile";
        return pakchunk_Md5;
    }
    pakchunk_Md5 = crypto.result().toHex();
    return pakchunk_Md5;
}

MainWindow2::MainWindow2(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow2)
{
    ui->setupUi(this);
}

MainWindow2::~MainWindow2()
{
    delete ui;
}

void MainWindow2::on_pushButton_clicked()
{
    int file_ok = 0;

    QFutureWatcher<void>* watcher = new QFutureWatcher<void>();
    connect(watcher, SIGNAL(finished()), this, SLOT(Md5_gen()));
    //file pak33
    QString loc33 = "/SM/test.pak";
    QFuture<QString> future33 = QtConcurrent::run(QThreadPool::globalInstance(), Md5_gen, loc33);
    QString pakchunk33 = future33.result();
    watcher->setFuture(future33);
    qDebug() << pakchunk33;
    if (pakchunk33 == "f7002d4419cd235a87746715ba6fb2ea")
    {
        qDebug() << "OK";
        file_ok++;
        ui->label_8->setText("OK");
        ui->label_8->setStyleSheet("QLabel { color : green; }");
    } else if (pakchunk33 == "nofile")
    {
        qDebug() << "no file found";
        ui->label_8->setText("not found");
        ui->label_8->setStyleSheet("QLabel { color : red; }");
    } else
    {
        qDebug() << "file is diffrent";
        ui->label_8->setText("wrong");
        ui->label_8->setStyleSheet("QLabel { color : red; }");
    }

    //file pak34
    QString loc34 = "/SM/test2.pak";
    QFuture<QString> future34 = QtConcurrent::run(QThreadPool::globalInstance(), Md5_gen, loc34);
    QString pakchunk34 = future34.result();
    qDebug() << pakchunk34;
    watcher->setFuture(future34);
    if (pakchunk34 == "64c77598586b6c3cb60beed0b0750620")
    {
        qDebug() << "OK";
        file_ok++;
        ui->label->setText("OK");
        ui->label->setStyleSheet("QLabel { color : green; }");
    } else if (pakchunk34 == "nofile")
    {
        qDebug() << "no file found";
        ui->label->setText("not found");
        ui->label->setStyleSheet("QLabel { color : red; }");
    } else
    {
        qDebug() << "file is diffrent";
        ui->label->setText("wrong");
        ui->label->setStyleSheet("QLabel { color : red; }");
    }

    //file pak35
    QString loc35 = "/SM/test3.pak";
    QFuture<QString> future35 = QtConcurrent::run(QThreadPool::globalInstance(), Md5_gen, loc35);
    QString pakchunk35 = future35.result();
    watcher->setFuture(future35);
    qDebug() << pakchunk35;
    if (pakchunk35 == "ee53f7a7656a32b5278c460baec46f16")
    {
        qDebug() << "OK";
        file_ok++;
        ui->label_7->setText("OK");
        ui->label_7->setStyleSheet("QLabel { color : green; }");
    } else if (pakchunk35 == "nofile")
    {
        qDebug() << "no file found";
        ui->label_7->setText("not found");
        ui->label_7->setStyleSheet("QLabel { color : red; }");
    } else
    {
        qDebug() << "file is diffrent";
        ui->label_7->setText("wrong");
        ui->label_7->setStyleSheet("QLabel { color : red; }");
    }
}

can anyone please help me find the problem

saeid0034

its fully fixed by adding qApp->processEvents(); to MD5 while

SGaist

You do realise that your code is wrong in terms of offloading the work ? As I already wrote: result will be blocking if the computation is not finished.

The idea is to use the watcher so you let the computation run and in the slot connected to your QFutureWatcher you run your UI updates.

What you have here is mostly the same code as before, but more complicated, since you are blocking your event loop with your calls to result.

aha_1980

Hi @saeid0034,

its fully fixed by adding qApp->processEvents(); to MD5 while

For sure not! Please don't use processEvents() if you don't know what you are doing!

Regards

saeid0034

@SGaist i don't know how correctly use QFutureWatcher in my code...
As you can see in my full cod in above im add QFutureWatcher to my cod, is it wrong?
Can you please guide me to how do this?

aha_1980

Hi @saeid0034,

As @SGaist already said, calling result() when the future is not done yet will block your event loop.

You should call result() in the slot connected to finished().

Regards

saeid0034

@aha_1980 thanks for information
problem is i dont know much about working with slots and QFutureWatcher
can you please say to me i need to do what with this code?

QString Md5_gen(QString const &s)
{
    QString pakchunk_Md5;
    QCryptographicHash crypto(QCryptographicHash::Md5);
    QFile pakchunk(QDir::currentPath() + s);
    if (pakchunk.open(QIODevice::ReadOnly))
    {
        while(!pakchunk.atEnd()){
        crypto.addData(pakchunk.read(8192));
        }
    } else
    {
        qDebug() << "Can't open file.";
        pakchunk_Md5 = "nofile";
        return pakchunk_Md5;
    }
    pakchunk_Md5 = crypto.result().toHex();
    return pakchunk_Md5;
}

MainWindow2::MainWindow2(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow2)
{
    ui->setupUi(this);
}

MainWindow2::~MainWindow2()
{
    delete ui;
}

void MainWindow2::on_pushButton_clicked()
{
    int file_ok = 0;

    QFutureWatcher<void>* watcher = new QFutureWatcher<void>();
    connect(watcher, SIGNAL(finished()), this, SLOT(Md5_gen()));
    //file pak33
    QString loc33 = "/SM/test.pak";
    QFuture<QString> future33 = QtConcurrent::run(QThreadPool::globalInstance(), Md5_gen, loc33);
    QString pakchunk33 = future33.result();
    watcher->setFuture(future33);
    qDebug() << pakchunk33;
    if (pakchunk33 == "f7002d4419cd235a87746715ba6fb2ea")
    {
        qDebug() << "OK";
        file_ok++;
        ui->label_8->setText("OK");
        ui->label_8->setStyleSheet("QLabel { color : green; }");
    } else if (pakchunk33 == "nofile")
    {
        qDebug() << "no file found";
        ui->label_8->setText("not found");
        ui->label_8->setStyleSheet("QLabel { color : red; }");
    } else
    {
        qDebug() << "file is diffrent";
        ui->label_8->setText("wrong");
        ui->label_8->setStyleSheet("QLabel { color : red; }");
    }

    //file pak34
    QString loc34 = "/SM/test2.pak";
    QFuture<QString> future34 = QtConcurrent::run(QThreadPool::globalInstance(), Md5_gen, loc34);
    QString pakchunk34 = future34.result();
    qDebug() << pakchunk34;
    watcher->setFuture(future34);
    if (pakchunk34 == "64c77598586b6c3cb60beed0b0750620")
    {
        qDebug() << "OK";
        file_ok++;
        ui->label->setText("OK");
        ui->label->setStyleSheet("QLabel { color : green; }");
    } else if (pakchunk34 == "nofile")
    {
        qDebug() << "no file found";
        ui->label->setText("not found");
        ui->label->setStyleSheet("QLabel { color : red; }");
    } else
    {
        qDebug() << "file is diffrent";
        ui->label->setText("wrong");
        ui->label->setStyleSheet("QLabel { color : red; }");
    }

    //file pak35
    QString loc35 = "/SM/test3.pak";
    QFuture<QString> future35 = QtConcurrent::run(QThreadPool::globalInstance(), Md5_gen, loc35);
    QString pakchunk35 = future35.result();
    watcher->setFuture(future35);
    qDebug() << pakchunk35;
    if (pakchunk35 == "ee53f7a7656a32b5278c460baec46f16")
    {
        qDebug() << "OK";
        file_ok++;
        ui->label_7->setText("OK");
        ui->label_7->setStyleSheet("QLabel { color : green; }");
    } else if (pakchunk35 == "nofile")
    {
        qDebug() << "no file found";
        ui->label_7->setText("not found");
        ui->label_7->setStyleSheet("QLabel { color : red; }");
    } else
    {
        qDebug() << "file is diffrent";
        ui->label_7->setText("wrong");
        ui->label_7->setStyleSheet("QLabel { color : red; }");
    }
}

aha_1980

Hi @saeid0034,

see e.g. this example.

Regards