What is the best way to put a class member function into another thread for execution?

Quiccz

I want to exec my member function in another thread. My function will emit some signals to change ui.
I tryed QtConcurrent::run(). But the slot won't exec in main thread. even if i connect them in main thread.

Use move to thread will move my class to thread, which is not i want. I just want to exec one function.
just like std::thread() run.

jsulm

@Quiccz said in What is the best way to put a class member function into another thread for execution?:

But the slot won't exec in main thread. even if i connect them in main thread.

How exactly do you connect?
You should go for worker object approach, see https://doc.qt.io/qt-6/qthread.html

Please post code as text, not pictures.

jeremy_k

@jsulm said in What is the best way to put a class member function into another thread for execution?:

Please post code as text, not pictures.

This post serves no purpose but to emphasize this point. I can't meaningfully quote an image. I can't easily view it with a smaller window or device. If I can't easily read it, it does not exist.

For a program written in plain text, post code in plain text.

J.Hilk

@Quiccz this is a recipe for disaster, and I'm not only talking about the image.

Those are not proper function pointers in your connect calls
sender and receiver are properly switched
The class is missing a constructor and base class initialisation
an endless while loop emitting millions of signals per seconds

I'm almost certain you don't need threads. At least with your so far shown expertise with c++ and Qt, it is going to cause way more problems than it will solve.

Quiccz

@J-Hilk I apologize for the confusion. What I wrote was just a piece of pseudo-code to express my logic, and it wasn't intended to be executed.

I try QThread finished my job.

#pragma once
#include <QThread>
#include <QDateTime>
class RegionManagerThread : public QThread
{
Q_OBJECT
public:
	RegionManagerThread(QVector<bool>* stop_vec, QVector<int> durations, int duration, qint64 start_time);
	void run() override;
signals:
	void preload();
	void finished();
	void stop(int i);

private:
	int m_duration;
	qint64 m_start_time;
	QVector<int> region_duration;
	QVector<bool>* m_region_stoped;
};

#include "region_manager_thread.h"
RegionManagerThread::RegionManagerThread(QVector<bool>* stop_vec, QVector<int> durations, int duration, qint64 start_time)
    : m_region_stoped(stop_vec),
    region_duration(durations),
    m_duration(duration),
    m_start_time(start_time)
{

}

void RegionManagerThread::run()
{
    bool preloaded = false;


    while (1)
    {
        if (!preloaded && QDateTime::currentDateTime().toMSecsSinceEpoch() - m_start_time >= m_duration - 4000)
        {
            preloaded = true;
            emit preload();
        }
        if (QDateTime::currentDateTime().toMSecsSinceEpoch() - m_start_time >= m_duration)
        {
            emit finished();
            return;
        }
        for (int i = 0; i < region_duration.size(); i++)
        {
            if (!(*m_region_stoped)[i] && QDateTime::currentDateTime().toMSecsSinceEpoch() - m_start_time >= region_duration[i])
            {
                emit stop(i);
            }
        }

        std::this_thread::sleep_for(std::chrono::milliseconds(2));
    }
}

However, assigning a member function from another class in the constructor feels inelegant to me. My idea is to run the "run" function as a member function of a class and only place it in another thread for execution, rather than the entire class.

J.Hilk

@Quiccz well it's somewhat better 🙈

anyway to your original question:

What is the best way to put a class member function into another thread for execution

The answer is:
https://doc.qt.io/qt-6/qthread.html#create

This is literally the purpose of that function. A QTfied wrapper around C++11’s std::thread

The this original post about it by KDAB for more detailed explanation:
https://www.kdab.com/new-qt-5-10-qthread-create/

Quiccz

@J-Hilk The result is same as QtConcurrent::run(). when i connect preload with QueuedConnection in main thread, then emit preload() in new thread. log shows me slot run in the new thread.

[thread 28644][scenes_widget.cpp:224][Play][debug] : here is main thread
[thread 33724][scenes_widget.cpp:345][ManagerRegions][info] : manager start
[thread 33724][program_widget.cpp:160][_PreLoad][info] : preload next