How to stop threads in Qt - c++

Question

What is the corrent way to stop threads in Qt?
Suppose that I have a worker (LicenseChecker class) and I want to do some actions every n seconds in the process member function. I need to do it indefinitely, until someone abort my loop.
_worker = new LicenseChecker;
_thread = new QThread;
_worker->moveToThread(_thread);
connect(_thread, SIGNAL(started()), _worker, SLOT(process()));
connect(_worker, SIGNAL(finished()), _thread, SLOT(quit()));
connect(_worker, SIGNAL(finished()), _worker, SLOT(deleteLater()));
connect(_thread, SIGNAL(finished()), _thread, SLOT(deleteLater()));
connect(_worker, SIGNAL(newLicensesActivated(QVector<LicenseInfo>)),
this, SLOT(newLicensesActivated(QVector<LicenseInfo>)));
_thread->start();
What can I do to abort it?
The first idea that I came up with was to define the sleep function as the following:
bool LicenseChecker::sleep(int seconds)
{
QTime end_time = QTime::currentTime().addSecs(seconds);
while (QTime::currentTime() < end_time)
{
QCoreApplication::processEvents(QEventLoop::AllEvents, 100);
QMutexLocker lock(&_abort_sync);
if (_abort)
{
return false;
}
}
return true;
}
and to check the return code of this function in my infinite loop:
while (true)
{
if (!sleep(5))
{
emit finished();
return;
}
// ...
}
And then on MainWindow's close event I need to do the following:
_worker->stop();
_thread->wait();
where stop member function just sets _abort data member to true, but the application hangs on these calls.
What is the right way to accomplish such task?

Answer 1

Seems that you call stop() from another thread (the main thread) but the worker instance is located in the worker thread. You can overcome this problem by carefully writing something like this to invoke a method from another thread:
void Worker::stop()
{
// make thread safe
if(QThread::currentThread() != this->thread())
{
this->metaObject()->invokeMethod(this, "stop", Qt::QueuedConnection);
return;
}
REAL CODE HERE ...
}
Besides that, i would rather use a timer to fire every n seconds to do the licence check. Something like that (example of an database connection checker):
dbCheckerThread = new QThread(this);
dbCheckerTimer = new QTimer();
dbCheckerTimer->setInterval(CHECKDBCONNECTIONINTERVALL);
dbCheckerTimer->moveToThread(dbCheckerThread);
dbChecker->moveToThread(dbCheckerThread);
connect(dbCheckerTimer, &QTimer::timeout, dbChecker, &DbConnectionChecker::checkConnection);
connect(dbCheckerThread, &QThread::started, dbCheckerTimer, static_cast<void (QTimer::*)(void)>(&QTimer::start));
dbCheckerThread->start();