QThread Basic use in c++ - c++

Question

I've got a c++ code including GUI, in which I need to run a time consuming loop for optimization.
class OptimizationAlgorith(data *data);
{
private:
var var1;
var var2;
public:
method1();
method2();
..
timeConsumingMethod(data);
}
this need to be called in a GUI class like following:
class QRegistration: public QWidget
{
Q_OBJECT
private:
data *m_data;
QPushButton *m_button_run;
OptimizationAlgorithm *m_optimizationalgorithm;
WorkerThread *m_workerThread;
QThread *m_thread;
..
private slots:
void on_pushButton_run_clicked();
void registrationDone();
I need to move the timeConsumingMethod into a seperate thread than main thread, so that the GUI does not freez while timeConsumingMethodis running.
I have made a new class "WorkerThread" using the official documentation of Qt, which looks like:
class WorkerThread : public QObject
{
Q_OBJECT
public:
WorkerThread(ApplicationData* data, QOptimizationAlgorithm * OptimizationAlgorithm);
~WorkerThread();
public slots:
void run(data* data);
signals:
void finished();
private slots:
private:
OptimizationAlgorithm *m_OptimizationAlgorithm;
ApplicationData *m_data;
}
How shoud I now implement my run()in WorkerThread? Can I simply write:
void WorkerThread::run(data *m_data)
{
m_optimization.timeConsumingMethod(m_data);
emit finished();
}
or do I have to copy the whole definition of timeConsumingMethod in run()? Why/Why not?

Answer 1

You don't need to do any explicit thread management, Qt already does it for you. Use QtConcurrent::run to do the work in a worker thread from the thread pool.
You should also decouple the controller that manages the work, and the UI. The knowledge of how to couple these objects should be separate from the objects themselves. This allows more flexibility in the design of the UI and the controller, and helps avoid several classes of errors that stem from accessing non-thread-safe methods from incorrect threads.
Complete example:
// https://github.com/KubaO/stackoverflown/tree/master/questions/threadwork-simple-40865259
#include <QtWidgets>
#include <QtConcurrent>
struct ApplicationData {};
struct OptimizationAlgorithm {
void timeConsumingMethod(QSharedPointer<ApplicationData>) {
QThread::sleep(3);
}
};
class Controller : public QObject {
Q_OBJECT
QSharedPointer<ApplicationData> m_data{new ApplicationData};
OptimizationAlgorithm m_algorithm;
public:
Q_SLOT void run() {
QtConcurrent::run([this]{
emit busy();
m_algorithm.timeConsumingMethod(m_data);
emit finished();
});
}
Q_SIGNAL void busy();
Q_SIGNAL void finished();
};
class Registration : public QWidget {
Q_OBJECT
QVBoxLayout m_layout{this};
QLabel m_status{"Idle"};
QPushButton m_run{"Run"};
public:
Registration() {
m_layout.addWidget(&m_status);
m_layout.addWidget(&m_run);
connect(&m_run, &QPushButton::clicked, this, &Registration::reqRun);
}
Q_SIGNAL void reqRun();
Q_SLOT void onBusy() { m_status.setText("Running"); }
Q_SLOT void onFinished() { m_status.setText("Idle"); }
};
void setup(Registration *reg, Controller *ctl) {
using Q = QObject;
Q::connect(reg, &Registration::reqRun, ctl, &Controller::run);
Q::connect(ctl, &Controller::busy, reg, &Registration::onBusy);
Q::connect(ctl, &Controller::finished, reg, &Registration::onFinished);
}
int main(int argc, char ** argv) {
QApplication app{argc, argv};
Controller ctl;
Registration reg;
setup(&reg, &ctl);
reg.show();
return app.exec();
}
#include "main.moc"