Using moveToThread for Worker Threads

This approach invovles moving a worker object to a dedicated thread, enabling background task execution. Synchronization is achieved using QMutex and QWaitCondition, particularly when the worker thread suspends itself and awaits a signal from the main thread.

Header File: TaskProcessor.h

#ifndef TASKPROCESSOR_H
#define TASKPROCESSOR_H

#include <QObject>
#include <QMutex>
#include <QWaitCondition>

class TaskProcessor : public QObject
{
    Q_OBJECT

public:
    explicit TaskProcessor(QObject* parent = nullptr);

public slots:
    void executeTask();
    void resumeTask();

signals:
    void taskResumed();
    void taskInitiated();

private slots:
    void handleResume();
    void handleInitiation();

private:
    QMutex lock;
    QWaitCondition pauseCondition;
};

#endif // TASKPROCESSOR_H

Implementation File: TaskProcessor.cpp

#include "TaskProcessor.h"
#include <QDebug>
#include <QThread>

TaskProcessor::TaskProcessor(QObject *parent)
    : QObject{parent}
{
    connect(this, &TaskProcessor::taskInitiated, this, &TaskProcessor::handleInitiation);
    connect(this, &TaskProcessor::taskResumed, this, &TaskProcessor::handleResume);
}

void TaskProcessor::executeTask()
{
    qDebug() << QThread::currentThreadId() << "Executing task";
    emit taskInitiated();
}

void TaskProcessor::resumeTask()
{
    qDebug() << QThread::currentThreadId() << "Resuming task";
    qDebug() << QThread::currentThreadId() << "Signaling condition";
    pauseCondition.wakeAll();
}

void TaskProcessor::handleResume()
{
    qDebug() << QThread::currentThreadId() << "Resume handled";
}

void TaskProcessor::handleInitiation()
{
    qDebug() << QThread::currentThreadId() << "Initiation handled";
    int counter = 0;
    while (true)
    {
        lock.lock();
        qDebug() << QThread::currentThreadId() << "Iteration" << counter;
        QThread::sleep(1);
        ++counter;

        if (counter % 5 == 0)
        {
            qDebug() << QThread::currentThreadId() << "Waiting at" << counter;
            pauseCondition.wait(&lock);
        }
        lock.unlock();
    }
}

Header File: Manager.h

#ifndef MANAGER_H
#define MANAGER_H

#include <QObject>

class TaskProcessor;

class Manager : public QObject
{
    Q_OBJECT

public:
    explicit Manager(QObject* parent = nullptr);
    ~Manager();

public slots:
    Q_INVOKABLE void startTask();
    Q_INVOKABLE void suspendTask();
    Q_INVOKABLE void continueTask();
    Q_INVOKABLE void validate();

private:
    QThread* workerThread;
    TaskProcessor* processor;
};

#endif // MANAGER_H

Implementation File: Manager.cpp

#include "Manager.h"
#include <QDebug>
#include <QThread>
#include "TaskProcessor.h"

Manager::Manager(QObject *parent)
    : QObject{parent}
{
    qDebug() << "Manager initialized";
    workerThread = new QThread;
    processor = new TaskProcessor;
    processor->moveToThread(workerThread);
    workerThread->start();
}

Manager::~Manager()
{
    qDebug() << QThread::currentThreadId() << "Manager cleanup";
    workerThread->terminate();
    if (workerThread->wait())
    {
        delete processor;
        delete workerThread;
    }
    qDebug() << QThread::currentThreadId() << "Cleanup complete";
}

void Manager::startTask()
{
    qDebug() << QThread::currentThreadId() << "Starting task";
    processor->executeTask();
}

void Manager::suspendTask()
{
    qDebug() << QThread::currentThreadId() << "Suspending task";
    // Suspension logic placeholder
}

void Manager::continueTask()
{
    qDebug() << QThread::currentThreadId() << "Continuing task";
    processor->resumeTask();
}

void Manager::validate()
{
    qDebug() << QThread::currentThreadId() << "Validation call";
}

QWaitCondition Methods

wakeAll

This method awakens all threads waiting on the condition. The order of awakening depends on the operating system's scheduling and cannot be predetermined.

wakeOne

This method awakens a single thread waiting on the condition. The specific thread awakened is determined by the OS scheduler. To target a particular thread, use separate wait conditions for different threads.

References

• QThread Class | Qt Core 5.15.15
• QThreadPool Class | Qt Core 5.15.15
• Synchronizing Threads | Qt 5.15
• QWaitCondition Class | Qt Core 5.15.15
• Wait Conditions Example | Qt Core 5.15.15