class MyWorker: public QThread
{
private:
    QMutex sync;
    QWaitCondition pauseCond;
    bool is_pause;

public:
    MyWorker(...): pause(false) {}

    void resume()
    {
        sync.lock();
        is_pause = false;
        sync.unlock();
        pauseCond.wakeAll();
    }

    void pause()
    {
        sync.lock();
        is_pause = true;
        sync.unlock();
    }

protected:
    void run()
    {
        while(someCondition) // gues it's your loop
        {
             sync.lock();
             if(is_pause)
                 pauseCond.wait(&sync); // in this place, your thread will stop to execute until someone calls resume
             sync.unlock();

             // do your operation
        }
    }
};