Stop Qt Thread : calling exit() or quit() does not stop the thread execution

Question

Created a QThread in main() i.e Main thread. Moved a worker class to the new thread. The thread executes the \'StartThread\' method of worker class.

Worker Thread:

Answer 1

isInterruptionRequested only returns true if you've called QThread::requestInterruption, not QThread::quit. This is documented.

If you want to use QThread::quit, the thread must spin an event loop, so you shouldn't be deriving from it; instead do this:

class Worker : public QObject {
  QBasicTimer m_timer;
  int chunksToDo = 20;
  void doChunkOfWork() {
    QThread::sleep(1);
  }
  void timerEvent(QTimerEvent * ev) {
    if (ev->timerId() != m_timer.timerId()) return;
    if (!chunksToDo) { m_timer.stop(); return; }
    doChunkOfWork();
    if (!--chunksToDo) emit done();
  }
public:
  explicit Worker(QObject * parent = nullptr) : QObject{parent} {
    m_timer.start(0, this);
  }
  Q_SIGNAL void done();
};

To run the worker, create it and move it to some its thread. To stop the worker, just quit() its thread before the worker is done.

int main(int argc, char ** argv) {
  QCoreApplication app{argc, argv};
  Worker worker;
  QThread thread;
  worker.moveToThread(&thread);
  QObject::connect(&worker, &Worker::done, &thread, &QThread::quit);
  QObject::connect(&thread, &QThread::finished, &app, &QCoreApplication::quit);
  thread.start();
  return app.exec();
}

Instead of managing the thread's life manually, you might wish to use a thread pool instead.

class Worker : public QObject, QRunnable {
  int chunksToDo = 20;
  volatile bool active = true;
  void doChunkOfWork() {
    QThread::sleep(1);
  }
  void run() {
    while (active && chunksToDo) {
      doChunkOfWork();
      --chunksToDo;
    }
    emit done();
  }
public:
  using QObject::QObject;
  Q_SLOT void stop() { active = false; }
  Q_SIGNAL void done();
};

int main(int argc, char ** argv) {
  QCoreApplication app{argc, argv};
  QThreadPool pool;
  Worker worker;
  worker.setAutoDelete(false); // important!
  pool.start(&worker);
  // *
  QTimer::singleShot(5000, &worker, &Worker::stop);
  QObject::connect(&worker, &Worker::done, &app, &QCoreApplication::quit);
  return app.exec();
}

An alternate way to end it without running the main event loop would have been:

  // *
  QThread::sleep(5);
  worker.stop();
  pool.waitForDone();
}

This answer has a complete example of streaming multiple jobs to a thread pool.