[SOLVED] Close a Qthread in the middle of it

[XGuy]

i have a QDialog and inside it's constructor a start a thread. but what if the user closes the dialog before thread is finished ? my solution was to implement closeEvent of the dialog so that i can quit the thread but still my app crashes ;-(

here is my code:

@
MyDialog::MyDialog() :
ui(new Ui::MyDialog)
{
QTimer::singleShot(50, this, SLOT(startThread()));
}

void MyDialog::startThread()
{
QObject::connect(&thrTest, SIGNAL(started()), &objAnotherClass, SLOT(sampleSlot()));
QObject::connect(&objAnotherClass, SIGNAL(sampleSlotFinished(int)), this, SLOT(sampleSlotFinished(int)));
objAnotherClass.moveToThread(&thrTest);
thrTest.start();
}

void MyDialog::sampleSlotFinished(int returnValue)
{
.
.
.
// QUIT THREAD
QObject::disconnect(&objAnotherClass, 0, 0, 0);
QObject::disconnect(&thrTest, 0, 0, 0);
thrTest.quit();
thrTest.exit(0);
}

void MyDialog::closeEvent(QCloseEvent *event)
{
Q_UNUSED(event);
if(thrTest.isRunning())
{
disconnect(&thrTest, 0, 0, 0);
disconnect(&objAnotherClass, 0, 0, 0);
thrTest.quit();
thrTest.exit(0);
thrTest.deleteLater();
objAnotherClass.deleteLater();
}
}

@

[Jeroentjehome]

Think in the closeEvent of the Dialog you need to wait until the QThread is done via:
@
while(isFinished() == false)
@ check. Then do the deletion of them all.
The problem is that your QThread object resides in the Dialog class. When you do a deleteLater on that one, if will get deleted when the dialog event queue is empty, but then the QThread object might not be ended. This probably causes the crash.

[XGuy]

thanks for reply.

i changed close event to below code:

@
void MyDialog::closeEvent(QCloseEvent *event)
{
Q_UNUSED(event);
if(thrTest.wait()) // block until thread is finished
{
disconnect(&thrTest, 0, 0, 0);
disconnect(&objAnotherClass, 0, 0, 0);
thrTest.deleteLater();
objAnotherClass.deleteLater();
}
}
@
but the problem is if i wait on that thread! it will also block the main thread(Caller Thread) so application won't respond untill this thread is finished!

[XGuy]

[quote author="Jeroentje@home" date="1383816067"]Think in the closeEvent of the Dialog you need to wait until the QThread is done via:
@
while(isFinished() == false)
@ check. Then do the deletion of them all.
The problem is that your QThread object resides in the Dialog class. When you do a deleteLater on that one, if will get deleted when the dialog event queue is empty, but then the QThread object might not be ended. This probably causes the crash. [/quote]

thanks for reply.

i changed close event to below code:
@
void MyDialog::closeEvent(QCloseEvent *event)
{
Q_UNUSED(event);
if(thrTest.wait()) // block until thread is finished
{
disconnect(&thrTest, 0, 0, 0);
disconnect(&objAnotherClass, 0, 0, 0);
thrTest.deleteLater();
objAnotherClass.deleteLater();
}
}
@

but the problem is if i wait on that thread! it will also block the main thread(Caller Thread) so application won’t respond untill this thread is finished!

[KA51O]

Have a look at "this thread":http://qt-project.org/forums/viewthread/34537/ , the problem is similar to yours.

[XGuy]

[quote author="KA51O" date="1383818721"]Have a look at "this thread":http://qt-project.org/forums/viewthread/34537/ , the problem is similar to yours.[/quote]

thanks for the link.
by reading that post i came to the idea of using boolean data members and always checking that members inside thread, sounds good!
i will happily accept any other workarounds.

[Jeroentjehome]

Chopping the worker object (that runs in the QThread) is a good idea and handling timing in the worker object. Then add a slot for the "StopObject" thread and your done. That's about the easiest way, so yes, checking boolean variables is not a problem. Or in the "stop" slot, close the file or other thing the thead has open. Delete all allocated memory and set this->deleteLater() and emit the finished signal to have the QThread that controls the object be closed and removed.
That should work fine.

[XGuy]

Thank you all.
i also encourage people with the same problem have a look at these two links which perfectly and simply cover how to use Qthread
"1st":https://fabienpn.wordpress.com/2013/05/01/qt-thread-simple-and-stable-with-sources/

"2nd":https://mayaposch.wordpress.com/2011/11/01/how-to-really-truly-use-qthreads-the-full-explanation/