[Qt-interest] QThread problem

[Donal O'Connor]

It is started in the render method.



On Wed, Nov 3, 2010 at 3:34 PM, prashant bhutani <
prashantbhutani2008 at gmail.com> wrote:

> Hi,
>
> Don't anyone think that in Mandlebort example thread "thread.start()" is
> missing?
> And without it how will the thread will execute?
>
> Prashant Bhutani
>
>
>
> On Wed, Nov 3, 2010 at 7:36 PM, <Oliver.Knoll at comit.ch> wrote:
>
>> On 2010-11-03 Joshua Joshua Wambua wrote:
>>
>> > Why don't you use a timer?
>>
>>
>> Timers are lame! Real men use threads ;)
>>
>> No seriously, the Qt Mandelbrot examples/threads/mandelbrot nicely shows
>> how to have a worker thread update the GUI with queued signals.
>>
>> Note the c'tor of the MandelbrotWidget:
>>
>> connect(&thread, SIGNAL(renderedImage(QImage,double)),
>>            this, SLOT(updatePixmap(QImage,double)));
>>
>> The 5th parameter of connect() defaults to Qt::AutoConnection, and since
>> the instances 'thread' and 'this' live in *different* threads (technically:
>> when http://doc.qt.nokia.com/4.7/qobject.html#thread returns different
>> values for the instances to be connected) this will evaluate to
>> Qt::QueuedConnection.
>>
>> And that is what you want: the worker threads tells: "Hey, I got some new
>> data, please render it". But since we all know that with Qt (and most other
>> GUI frameworks) the widgets must not be updated within any other thread than
>> the main thread (technically: where the QApplication instance "lives" in,
>> aka "GUI thread"), the actual slot - which draws the widgets etc. - must be
>> executed within the GUI thread. And that is exactly where the
>> Qt::QueuedConnections are helpful!
>>
>> But keep in mind that Queued Connections don't help you in avoiding
>> concurrent access to your data! Read about QSemaphore and Co.:
>> http://doc.trolltech.com/4.7/threads.html
>>
>>
>> Cheers, Oliver
>> --
>> Oliver Knoll
>> Dipl. Informatik-Ing. ETH
>> COMIT AG - ++41 79 520 95 22
>>
>>
>>
>> _______________________________________________
>> Qt-interest mailing list
>> Qt-interest at trolltech.com
>> http://lists.trolltech.com/mailman/listinfo/qt-interest
>>
>
>
> _______________________________________________
> Qt-interest mailing list
> Qt-interest at trolltech.com
> http://lists.trolltech.com/mailman/listinfo/qt-interest
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.qt-project.org/pipermail/qt-interest-old/attachments/20101103/6b0992bd/attachment.html