QThread slot executed in GUI thread

[tnyblom]

Hi,

I've got a GUI application (QApplication) that has a QMainWindow as the GUI. In this I have a button that triggers an action that should be executed in a thread. To achieve this I connect the buttons clicked() signal to a slot in the thread object. However the threads action is executed in the GUI thread.

Problem can be seen with the code below. On (at least) the second click on the button in the GUI I want the GUI to remain responsive and the thread to sleep.

Does anyone have an idea as to what I am doing wrong?

main.cpp

#include <QtGui/QApplication>
#include <QDebug>
#include "mainwindow.h"
 
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    qDebug() << "main:" << a.thread();
    return a.exec();
}

#include <QtGui/QApplication>
#include <QDebug>
#include "mainwindow.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    qDebug() << "main:" << a.thread();
    return a.exec();
}

To copy to clipboard, switch view to plain text mode 

thread.h

#ifndef THREAD_H
#define THREAD_H
 
#include <QThread>
 
class Thread : public QThread
{
    Q_OBJECT
public:
    explicit Thread(QObject *parent = 0);
    void run();
 
signals:
    void WorkDone();
 
public slots:
    void DoWork();
};
 
#endif // THREAD_H

#ifndef THREAD_H
#define THREAD_H

#include <QThread>

class Thread : public QThread
{
    Q_OBJECT
public:
    explicit Thread(QObject *parent = 0);
    void run();

signals:
    void WorkDone();

public slots:
    void DoWork();
};

#endif // THREAD_H

To copy to clipboard, switch view to plain text mode 

thread.cpp

#include "thread.h"
 
#include <QDebug>
 
Thread::Thread(QObject *parent) :
    QThread(parent)
{
    qDebug() << "Creating new Thread" << QThread::currentThreadId();
}
 
void Thread::run()
{
    qDebug() << "run:" << QThread::currentThreadId();
    exec();
}
 
void Thread::DoWork()
{
    qDebug() << "Thread::DoWork() in thread:" << QThread::currentThreadId();
    sleep(10);
}

#include "thread.h"

#include <QDebug>

Thread::Thread(QObject *parent) :
    QThread(parent)
{
    qDebug() << "Creating new Thread" << QThread::currentThreadId();
}

void Thread::run()
{
    qDebug() << "run:" << QThread::currentThreadId();
    exec();
}

void Thread::DoWork()
{
    qDebug() << "Thread::DoWork() in thread:" << QThread::currentThreadId();
    sleep(10);
}

To copy to clipboard, switch view to plain text mode 

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
 
#include "thread.h"
 
#include <QMainWindow>
 
class MainWindow : public QMainWindow
{
    Q_OBJECT
 
public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();
 
private:
    Thread thread;
};
 
#endif // MAINWINDOW_H

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include "thread.h"

#include <QMainWindow>

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

private:
    Thread thread;
};

#endif // MAINWINDOW_H

To copy to clipboard, switch view to plain text mode 

mainwindow.cpp

#include "mainwindow.h"
 
#include <QtGui>
#include <QDebug>
 
MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent)
{
    qDebug() << "MainWindow:" << this;
    QWidget *widget = new QWidget();
    QHBoxLayout *layout = new QHBoxLayout(widget);
    QPushButton *button = new QPushButton("Do work...", widget);
    widget->setLayout(layout);
    layout->addWidget(button);
    setCentralWidget(widget);
    thread.start();
    connect(button, SIGNAL(clicked()), &thread, SLOT(DoWork()));
}
 
MainWindow::~MainWindow()
{
    thread.exit();
    thread.wait();
}

#include "mainwindow.h"

#include <QtGui>
#include <QDebug>

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent)
{
    qDebug() << "MainWindow:" << this;
    QWidget *widget = new QWidget();
    QHBoxLayout *layout = new QHBoxLayout(widget);
    QPushButton *button = new QPushButton("Do work...", widget);
    widget->setLayout(layout);
    layout->addWidget(button);
    setCentralWidget(widget);
    thread.start();
    connect(button, SIGNAL(clicked()), &thread, SLOT(DoWork()));
}

MainWindow::~MainWindow()
{
    thread.exit();
    thread.wait();
}

To copy to clipboard, switch view to plain text mode