How to exit from QThread::wait() - c++

Question

I am using QThread for some huge task in background, here is sample
code i am using
class Worker : public QObject
{
Q_OBJECT
QThread workerThread;
public slots:
void doWork(const QString &parameter) {
while(1){
// some huge code here
......................
if(condition) break;
}
emit resultReady(result);
}
signals:
void resultReady(const QString &result);
};
class Controller : public QObject
{
Q_OBJECT
QThread workerThread;
public:
Controller() {
Worker *worker = new Worker;
worker->moveToThread(&workerThread);
connect(&workerThread, SIGNAL(finished()), worker, SLOT(deleteLater()));
connect(this, SIGNAL(operate(QString)), worker, SLOT(doWork(QString)));
connect(worker, SIGNAL(resultReady(QString)), this, SLOT(handleResults(QString)));
workerThread.start();
}
~Controller() {
workerThread.quit();
workerThread.wait();
}
public slots:
void handleResults(const QString &);
signals:
void operate(const QString &);
};
Is it recommended to use wait() after quit in above program?
My program sometimes stuck on QThread::wait(), it is downloading huge file from server and it take about 5-6 min to again check for while condition , I just want to exit from thread but main thread stuck at wait(), is there any way?? to exit or kill thread forcefully without crash or hang main application? I also tried QThread::terminated but it never works.
Any Help appreciated.
Thanks.

Answer 1

First of all it is not clear what you are doing at your thread from your above codes. Your first point of concentration is your method which is running inside your thread i.e. your thread object. First of all, why sometime your thread does not complete its task? and why it stuck? Here I can see a while loop with a condition always true. Probably you have some break statement inside the loop which sometimes never satisfy and because of that thread never complete as while loop is continuing. Just check closely what going wrong there. If while loop is creating the issue I can advice you with the following modification in your code. But you must be very careful because it should not exit before completing some very important task.
First modify your while loop like below:-
introduce one bool variable before the while loop
bool continued = true;
while(continued)
{
//your codes
}
Now add one method in your thread object Worker
void stopWorker()
{
continued = false;
}
Now just call this method when you want your thread to exit by force
worker->stopWorker();

Answer 2

Since Qt 5.2 there is a QThread::requestInterruption() this function alone that can e used to signal to your thread that it should stop working, however you MUST check in you long operation for QThread::isInterruptionRequested() and quit your loop or event loop:
http://doc.qt.io/qt-5/qthread.html#isInterruptionRequested

Answer 3

Official documentation for QThread class says:
bool QThread::wait(unsigned long time = ULONG_MAX)
Blocks the thread until either of these conditions is met:
The thread associated with this QThread object has finished execution (i.e. when it returns from run()). This function will return true if the thread has finished. It also returns true if the thread has not been started yet.
time milliseconds has elapsed. If time is ULONG_MAX (the default), then the wait will never timeout (the thread must return from run()). This function will return false if the wait timed out.
As you can see, ULONG_MAX is the default parameter for the method, and it forces the method to never timeout.
Is it a choice to add your own timeout in the method parameter?