On QHTTP::request() method.

[zgulser]

Hi,

I've just received an old project which some tasks needs to be fullfilled. I know the QHttp class is deprecated and shouldn't be used but I have a time issue that forces me to perform some quicky workarounds on the code without gettings hands dirty in refactoring in order to migrate to QNetworkAccessManager.

I have a question about QHttp class as you might guess. I wonder if do I need to use a seperate thread for network operations performed over QHttp class? As far as I remember, QNetworkAccessManager has it's own internal/seemless worker threads that gets the job done. Is it also similar for example QHttp::request() method as well? I mean do I need to create a worker thread explicitly for a network operation if I use QHttp class?

Regards

[ChrisW67]

No. No user threads are required for Qt networking (until recently there were no threads used by Qt networking internally either).

[zgulser]

First of all, thanks for your response.

until recently there were no threads used by Qt networking internally either

How the long time running network operations performed then?

[ChrisW67]

Asynchronously with signals and slots, exactly as described in the documentation.

[zgulser]

Pardon me. I understand what you want to point out but it's also stated in the documentation that Http::request() is not a blocking method. Thus, if I call the request from UI thread, it should process the request(QHttp::request()) in a worker thread in order not to block.

The signal-slot mechanism you mentioned should be used to update UI thread from the worker one. Am I wrong?

[ChrisW67]

Yes, you are wrong. You said it yourself, the request(), get(), post() and head() methods do not block the UI thread. When a request completes, the state changes, or data is available you will see a signal from the QHttp object announcing that.

Here is a complete example showing the UI is responsive during a longer (22MB) download. Try resizing as it runs.:

#include <QApplication>
#include <QVBoxLayout>
#include <QLabel>
#include <QTimer>
#include <QHttp>
 
class Widget: public QWidget {
    Q_OBJECT
 
    QTimer *timer;
    QHttp *http;
    QLabel *timerLabel;
    QLabel *infoLabel;
    int tick;
    int bytes;
 
public:
    Widget(QWidget *p = 0): QWidget(p) {
        timerLabel = new QLabel("", this);
        infoLabel = new QLabel("", this);
        QVBoxLayout *layout = new QVBoxLayout(this);
        layout->addWidget(timerLabel);
        layout->addWidget(infoLabel);
 
        QTimer *timer = new QTimer(this);
        connect(timer, SIGNAL(timeout()), SLOT(handleTimer()));
        timer->setInterval(1000);
        timer->start();
 
        http = new QHttp(this);
        connect(http, SIGNAL(requestStarted(int)), SLOT(handleStarted(int)));
        connect(http, SIGNAL(readyRead(QHttpResponseHeader)), SLOT(handleRead(QHttpResponseHeader)));
        connect(http, SIGNAL(requestFinished(int,bool)), SLOT(handleFinished(int,bool)));
 
        http->setHost("www.nasa.gov");
        http->get("/sites/default/files/pia17582.jpg");
 
        tick = 0;
        bytes = 0;
    }
 
private slots:
    void handleTimer() {
        timerLabel->setText(QString::number(tick++));
    }
    void handleStarted(int id) {
        infoLabel->setText(QString("Request %1 started").arg(id));
    }
    void handleRead(const QHttpResponseHeader &header) {
        QByteArray ba = http->readAll();
        bytes += ba.size();
        infoLabel->setText(QString("Read %1 bytes").arg(bytes));
    }
    void handleFinished(int id, bool error) {
        infoLabel->setText(QString("Request %1 finished").arg(id));
    }
};
 
int main(int argc, char **argv)
{
    QApplication app(argc, argv);
    Widget w;
    w.show();
    return app.exec();
}
#include "main.moc"

#include <QApplication>
#include <QVBoxLayout>
#include <QLabel>
#include <QTimer>
#include <QHttp>

class Widget: public QWidget {
    Q_OBJECT

    QTimer *timer;
    QHttp *http;
    QLabel *timerLabel;
    QLabel *infoLabel;
    int tick;
    int bytes;

public:
    Widget(QWidget *p = 0): QWidget(p) {
        timerLabel = new QLabel("", this);
        infoLabel = new QLabel("", this);
        QVBoxLayout *layout = new QVBoxLayout(this);
        layout->addWidget(timerLabel);
        layout->addWidget(infoLabel);

        QTimer *timer = new QTimer(this);
        connect(timer, SIGNAL(timeout()), SLOT(handleTimer()));
        timer->setInterval(1000);
        timer->start();

        http = new QHttp(this);
        connect(http, SIGNAL(requestStarted(int)), SLOT(handleStarted(int)));
        connect(http, SIGNAL(readyRead(QHttpResponseHeader)), SLOT(handleRead(QHttpResponseHeader)));
        connect(http, SIGNAL(requestFinished(int,bool)), SLOT(handleFinished(int,bool)));

        http->setHost("www.nasa.gov");
        http->get("/sites/default/files/pia17582.jpg");

        tick = 0;
        bytes = 0;
    }

private slots:
    void handleTimer() {
        timerLabel->setText(QString::number(tick++));
    }
    void handleStarted(int id) {
        infoLabel->setText(QString("Request %1 started").arg(id));
    }
    void handleRead(const QHttpResponseHeader &header) {
        QByteArray ba = http->readAll();
        bytes += ba.size();
        infoLabel->setText(QString("Read %1 bytes").arg(bytes));
    }
    void handleFinished(int id, bool error) {
        infoLabel->setText(QString("Request %1 finished").arg(id));
    }
};

int main(int argc, char **argv)
{
    QApplication app(argc, argv);
    Widget w;
    w.show();
    return app.exec();
}
#include "main.moc"

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[zgulser]

Hi,

I exactly understood what you told about async signal-slot messaging. I'm only saying this messaging should be a type of queued connection since signal receiver is in the UI thread where sender is not.

Thanks for your valuable responses by the way.

[anda_skoa]

The sender (QHttp) is also in the UI thread.
Even if it were not, Qt::AutoConnection would take care of the thread bridiging.
But, again, this is not the case here since there is only one thread involved.

Cheers,
_