[Qt-interest] Warning: QObject::startTimer: timers cannot be started from another thread

[Sean Harmer]

On Monday 22 March 2010 08:29:03 Eirik Ulvik wrote:
> Den 18.03.2010 21:03, skrev Sean Harmer:
> > Hi,
> > 
> > Eirik Ulvik wrote:
> >> I am in the process of making our application multithreaded. The problem
> >> I am now facing is the error message in the subject is printed all the
> >> time while executing the program. I also get the same sort of message
> >> for QObject::killTimer. After googling a bit I found, as expected, that
> >> this is related to doing GUI operation in threads other than the main Qt
> >> GUI thread.
> >> 
> >> My next step is to strip all GUI operations from the code that runs in a
> >> separate thread. As much of this code is quite old and did not separate
> >> GUI code from other code, locating the code in question is difficult. So
> >> my question to the list is if anyone has had experience in a similar
> >> situation or have some general pointers on good ways of pin pointing GUI
> >> code I would be very grateful.
> > 
> > Do either:
> > 
> > (1) Set break points on all occurrances of startTimer()
> > (2) Set break point in QObject::startTimer() and look at the stack to
> > see where it is being called in your code.
> > (3) export the Q_FATAL_WARNINGS environment variable and run your app in
> > a debugger. It will abort whenever Qt issues a warning. Again look at
> > the stack to see where in your code it is being triggered.
> > 
> > Once you find where it is being called, find from which thread's context
> > it is being called and fix it ;-) Once you find the problem spots and
> > can make a small compileable example for each type of problem post it to
> > the list and we can tell you how to resolve them.
> > 
> > A good approach when using QObjects in worker threads is to not make
> > your QThread subclass do the work. This is because the thread object
> > itself has affinity with the thread that created it - usually the main
> > GUI thread. Instead, create a QObject derived object in the QThread's
> > run() function and have that do the work instead. That way, your QObject
> > will have affinity with the worker thread and not the main thread.
> > 
> > Good luck,
> > 
> > Sean
> > _______________________________________________
> > Qt-interest mailing list
> > Qt-interest at trolltech.com
> > http://lists.trolltech.com/mailman/listinfo/qt-interest
> 
> Thanks a lot for your reply. I will give this a try. Btw. I think the Qt
> macro should be QT_FATAL_WARNINGS.

Ah yes, sorry. My bad.

Sean