[Interest] Terminating a QThread

[Etienne Sandré-Chardonnal]

Well, after a quick test, it seems that terminate is not working under
windows (at least, not working as expected by reading the manual).

That's a very good occasion for you to re-think your code and make it work
without terminate. There is nothing less clean than terminate (just remind
that, amongst other risks, terminate() can let your memory allocator in an
undefined state, crashing your whole app). Terminate should'nt even be in
Qt framework IMHO... You can't say than adding some code to poll for a flag
and exit the worker code is not clean. It's just some extra work, for the
stake of having an app that will not segfault.

Etienne


2013/6/21 francois cellier <f_cellier at yahoo.fr>

> Thanks Etienne and Mandeep for your answers.
>
> However as I wrote in my initial post (in the code of the objectInThread
> class), in my real application I do not have a while loop just a sequence
> of functions. With a while loop and the flag the code is clean like that.
> However, in my case that means I need to check that flag from many classes.
> For now I did the approach that you were talking using a singleton to get
> an easy access to that flag from many different classes and I find this not
> so clean...
>
> However even without speaking about clean things or things to avoid, I
> would like to know why the terminate function does not terminate my thread
> if an eventloop is running.
>
>
>   ------------------------------
>  *De :* Etienne Sandré-Chardonnal <etienne.sandre at m4x.org>
> *À :*
> *Cc :* "interest at qt-project.org" <interest at qt-project.org>
> *Envoyé le :* Vendredi 21 juin 2013 13h00
> *Objet :* Re: [Interest] Terminating a QThread
>
> Sorry Mandeep, I didn't read your post first. Basically what I posted is
> similar.
>
> A mutex is a little bit overkill here, you could use an atomic variable if
> you want to be sure, but just a bool flag will be enough as it is always
> set atomically AFAIK
>
>
> 2013/6/21 Mandeep Sandhu <mandeepsandhu.chd at gmail.com>
>
> On Fri, Jun 21, 2013 at 1:36 PM, francois cellier <f_cellier at yahoo.fr>wrote:
>
> Dear all,
>
> Even if I know that it can be dangerous to terminate a thread, I need to
> do it for my application.
> The function that run into the thread is like a long linear sequence of
> code that has not been designed in a signal/slot way. Moreover, in my
> thread, I need an eventloop as I use in it some TCP or UDP  Qt sockets.
>
> I have tried the worker approach with the following code and I did not
> find a way to terminate the thread :
>
> For my thread class :
>
>    1. ThreadEx::ThreadEx(QObject <http://qt-project.org/doc/QObject.html>
>    *parent) :
>    2.     QThread <http://qt-project.org/doc/QThread.html>(parent)
>    3. {
>    4. }
>    5.
>    6. void ThreadEx::run()
>    7. {
>    8.     QThread <http://qt-project.org/doc/QThread.html>::
>    setTerminationEnabled(true);
>    9.     exec();
>    10. }
>
>
>
> For my worker class:
>
>    1. ObjectInThread::ObjectInThread(QObject<http://qt-project.org/doc/QObject.html>
>    *parent) :
>    2.     QObject <http://qt-project.org/doc/QObject.html>(parent)
>    3. {
>    4. }
>    5.
>    6.
>    7. void ObjectInThread::run()
>    8. {
>    9.    int compteur = 0;
>    10. //here i am using a loop instead of the long linear flow  but it
>    is not a loop  in the real code
>    11.     while(1)
>    12.     {
>    13.         qDebug() <<compteur;
>    14.         compteur++;
>    15.         Sleep(1000);
>    16.     }
>    17. }
>
> You use a condition variable in your loop here, which will exit out of the
> run() function. This variable can be set from your stop() slot (protected
> by a mutex if needed).
> In your main(GUI) thread you can wait for your worker thread to exit:
>
> m_thread->quit();
> m_thread->wait();
>
> HTH,
> -mandeep
>
>
> This should cleanly exit the thread.
>
>
>  Moreover I tried the other way of using QThread that consists in
> inheriting the QThread class and overriding the run method with the code :
>
> void ThreadEx::run()
> {
>     int compteur = 0;
>     while(1)
>     {
>          qDebug() <<compteur;
>          compteur++;
>          sleep(1);
>     }
> }
>
> In that case terminate works but I do not have an eventloop as I did not
> call the exec method.
>
> Is this the expected behaviour ?
>
> I am using Qt5.1 on centOS / RedHat 6.2. I have also tried this on Windows
> with no more success.
>
> Thanks for your help,
> François
>
>
>
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