Simple QThread class and QObject::moveToThread() - questions

[_franko_]

Hi all,

I'm new to threading in Qt.
I have several questions regarding the following class. I hope that wise programmers of this forum will help me better understand the QThread class and how does threads works in Qt.

thread1.h

#ifndef THREAD1_H
#define THREAD1_H
 
#include <QThread>
#include <QTimer>
 
class Thread1 : public QThread
{
    Q_OBJECT
public:
    Thread1();
    ~Thread1();
 
protected:
    void run();
 
signals:
    void sigThreadQuit();
 
public slots:
    void sTimeout();
 
private:
    QTimer* timer1;
    QTimer timer2;
 
    int counter;
};
 
#endif // THREAD1_H

#ifndef THREAD1_H
#define THREAD1_H

#include <QThread>
#include <QTimer>

class Thread1 : public QThread
{
    Q_OBJECT
public:
    Thread1();
    ~Thread1();

protected:
    void run();

signals:
    void sigThreadQuit();

public slots:
    void sTimeout();

private:
    QTimer* timer1;
    QTimer timer2;

    int counter;
};

#endif // THREAD1_H

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thread1.cpp

#include "thread1.h"
 
Thread1::Thread1():
        timer1(new QTimer(this)), counter(0)
{
    qDebug("Thread1(): Creating...");
    timer1->setInterval(1000);
    timer2.setInterval(1000);
 
    connect(timer1, SIGNAL(timeout()), this, SLOT(sTimeout()));
    connect(&timer2, SIGNAL(timeout()), this, SLOT(sTimeout()));
 
    moveToThread(this);
}
 
Thread1::~Thread1() {
    qDebug("~Thread1(): Destroyed.");
}
 
void Thread1::run() {
    qDebug("Thread1::run(): Running...");
    timer1->start();
    timer2.start();
    exec();
}
 
void Thread1::sTimeout() {
    QTimer* t = (QTimer*) sender();
    qDebug("sTimeout(): Timer: %p; Counter: %d", t, counter);
    if(counter > 10)
        emit sigThreadQuit();
    counter++;
}

#include "thread1.h"

Thread1::Thread1():
        timer1(new QTimer(this)), counter(0)
{
    qDebug("Thread1(): Creating...");
    timer1->setInterval(1000);
    timer2.setInterval(1000);

    connect(timer1, SIGNAL(timeout()), this, SLOT(sTimeout()));
    connect(&timer2, SIGNAL(timeout()), this, SLOT(sTimeout()));

    moveToThread(this);
}

Thread1::~Thread1() {
    qDebug("~Thread1(): Destroyed.");
}

void Thread1::run() {
    qDebug("Thread1::run(): Running...");
    timer1->start();
    timer2.start();
    exec();
}

void Thread1::sTimeout() {
    QTimer* t = (QTimer*) sender();
    qDebug("sTimeout(): Timer: %p; Counter: %d", t, counter);
    if(counter > 10)
        emit sigThreadQuit();
    counter++;
}

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main.cpp

#include <QtCore/QCoreApplication>
 
#include "thread1.h"
#include "thread2.h"
 
int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    qDebug("Main start");
 
//    Thread1* t1 = new Thread1();
 
    Thread1 t2;
 
//    Thread2 t2;
 
    //    a.connect(t1, SIGNAL(sigThreadQuit()), &a, SLOT(quit()));
    a.connect(&t2, SIGNAL(sigThreadQuit()), &a, SLOT(quit()));
 
//    t1->start();
    t2.start();
 
    int retvel = a.exec();
 
    qDebug("Main end");
    return retvel;
}

#include <QtCore/QCoreApplication>

#include "thread1.h"
#include "thread2.h"

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    qDebug("Main start");

//    Thread1* t1 = new Thread1();

    Thread1 t2;

//    Thread2 t2;

    //    a.connect(t1, SIGNAL(sigThreadQuit()), &a, SLOT(quit()));
    a.connect(&t2, SIGNAL(sigThreadQuit()), &a, SLOT(quit()));

//    t1->start();
    t2.start();

    int retvel = a.exec();

    qDebug("Main end");
    return retvel;
}

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The main function creates an object of class Thread1, which is designed to display text and after 10 seconds to send a signal to finish the thread.
After creating a t2 object, signal sending by a thread is connected with the slot quit() of the main application.
In the above class, I have two objects QTimer - one of them is a pointer.
After running the application I see that only one timer is working - a pointer.

Here are my questions:
1. Why I can not see the operation of the QTimer object which is not a pointer? Does is not running?
2. If I don't use function moveToThread() for instance in the constructor of Thread1 class, then QTimer objects (or a thread), do not start in general. I think that it has something with main a.exec() function. Why and what?
3. Does the above example is written correctly with the principles of multithreaded programming in Qt?

I wrote this class for understanding Qt thread support. Any posts with good explanations and links are welcome.

Thank you for any answers

[MarekR22]

1. Never ever move thread to it self! Moving QObject to thread means that connected (see Qt::ConnectionType-enum) slots will be run in thread they were move to!
2. moveToThread works only when object doesn't have a parent! See QObject::moveToThread
3. Read this

[_franko_]

Thank you for your post.

Third answer has me thinking. So now I have to redesign my class and read once again docs and tutorials carefully.

Thanks.