Qt threads - new way verification please

Question

So new to Qt. Read the wiki and C++ Gui programming book and they say subclass QThread. Found that this is not the recommended way now.

So I have some practice code here and I have some questions about if this is correct. So I would really appreciate someone having a look please.

So I created a class with the QThread as a private member to use for the movetothread. When creating it, I made sure not to specify a parent. Therefore my first question is, is this ok to do?

Second question comes from the m_thread->quit(); I found that my connect to finished wasn't being emitted until I did this. So is this the correct way? I read http://mayaposch.wordpress.com/2011/11/01/how-to-really-truly-use-qthreads-the-full-explanation/ and saw that the connect between finished and deleteLater in the same thread but not 100% sure if this should be used with quit.

Finally, with the talk of deleteLater, does this mean I dont need delete m_thread

Thanks for anyones time.

Code here. Simple QDialog with a pushbutton. worker.cpp

#include "worker.h"

worker::worker(QObject *parent) :
    QObject(parent)
{
    stopped = false;
}

void worker::setupAndRun()
{
    m_thread = new QThread();
    connect(m_thread,SIGNAL(started()),this,SLOT(doWork()));
    connect(m_thread,SIGNAL(finished()),this,SLOT(onComplete()));
    connect(m_thread,SIGNAL(finished()),m_thread,SLOT(deleteLater()));
    this->moveToThread(m_thread);
    m_thread->start();
}

void worker::doWork()
{

    for(int i = 0; i < 20000; i++)
    {
        if (this->stopped)
            break;
        qDebug() << i << " : " <<  Q_FUNC_INFO << m_thread->currentThreadId();
    }
    // --- I think the quit calls the finished signal?
    m_thread->quit();

}

void worker::onComplete()
{
    qDebug() <<  Q_FUNC_INFO << "Called " << m_thread->currentThreadId();
}

worker.h

#ifndef WORKER_H
#define WORKER_H

#include <QObject>
#include <QDebug>
#include <QThread>

class worker : public QObject
{
    Q_OBJECT
public:
    explicit worker(QObject *parent = 0);
    void setupAndRun();
signals:

public slots:
    void doWork();
    void onComplete();
private:
    // --- The thread that I use to movetothread with.
    // Is this ok?
    QThread *m_thread;
    bool stopped;
};

#endif // WORKER_H

Dialog push button

void Dialog::on_pushButton_clicked()
{
    m_worker = new worker();
    m_worker->setupAndRun();
}

hyde hyde · Accepted Answer · 2012-10-17T10:47:41

I did not spot anything much at a glance, but something:

Since m_thread is member variable, you should handle it a bit differently. You could initialize it to null in the constructor, and also set m_thread = null after calling m_thread->quit(), since it will get deleted shortly after and you do not want a dangling pointer.

With this code, you should connect the finished signal to m_worker's deleteLater() too, as it appears there is no other code to delete that. You should also take care of threads when application exits, for example with qAddPostRoutine, so that all threads terminate and all related objects get deleted.

Qt threads - new way verification please

1 Answers