[Qt-interest] QT3's postEvent VS QT4's connect (blocking queued connection)

[Neeraj Jhawar]

Sir,

The problem that I wish to solve is that QT system ( the new thread) takes
regular inputs (at 100 ms interval) from RTLinux and shows it in the GUI. I
have been able to design the connection between QT and RT in the thread but
the problem comes when i try to show it in QT GUI. I need to show it every
100 or so ms and not more. But the postEvent application says it waits till
the event is called and " The event will be delivered later on by the GUI
thread." I dont want this. I need a constant connection between the threads
SIGNAL and the SLOT which will be responsible to show the details in GUI. I
had read this is possible by connect if you give is blocking queued
connection.
So I have started with installation of QT4 (though seriously I dont prefer
doing it at this stage of my project).
If such a thing (as desired by me) is possible in with postEvent ... please
apprise me of the same.


On Sat, Jan 10, 2009 at 1:28 PM, Malyushytsky, Alex <alex at wai.com> wrote:

>  I don't have link to QT3 documentation, other than
>
> http://www.mathematik.uni-ulm.de/help/qt-2.3.1/threads.html
>
>
>
> But if You have QT 3 installed you should have documentation.
>
>
>
> Search for "Thread Support in Qt" there.
>
>
>
>
>
> In short, use
>
>   QApplication::postEvent  to send events safely. (don't use sentEvent)
>
>
>
> From documentation:
>
>
>
> Thread-safe Event Posting
>
> In Qt, one thread is always the GUI or event thread. This is the thread
> that creates a QApplication object and calls QApplication::exec(). This is
> also the initial thread that calls main() at program start. This thread is
> the only thread that is allowed to perform GUI operations, including
> generating and receiving events from the window system. Qt does not support
> creating QApplication and running the event loop (with QApplication::exec())
> in a secondary thread. You must create the QApplication object and call
> QApplication::exec() from the main() function in your program.
>
> Threads that wish to display data in a widget cannot modify the widget
> directly, so they must post an event to the widget using
> QApplication::postEvent(). The event will be delivered later on by the GUI
> thread.
>
> Normally, the programmer would like to include some information in the
> event sent to the widget. See the documentation for QCustomEvent for more
> information on user-defined events.
>
>
>
>
>
> I would recommend QT4 if the code is new or small.
>
> Depending on the complexety of your code, porting might be very time
> consuming task,.
>
> In some cases it would be faster to write application from the scratch..
>
>
>
> Also try to create thread with subject – this way you can get more help.
>
>
>
> Best regards,
>
> Alex
>
>
>
>
>  ------------------------------
>
> *From:* qt-interest-bounces at trolltech.com [mailto:
> qt-interest-bounces at trolltech.com] *On Behalf Of *Neeraj Jhawar
> *Sent:* Friday, January 09, 2009 6:38 PM
> *To:* qt-interest at trolltech.com
> *Subject:* Re: [Qt-interest] (no subject)
>
>
>
> Hello Everyone
>
>
> I am using QT3 and wish to do some cross thread communication between two
> threads in QT. I learnt that this can only be done using event in QT3.
>
> Could someone please throw some light on how to get it done.
>
> Also if possible, any supplement link or material would be of great help.
>
> Thx
>
> Sincerely,
>
> On Sat, Jan 10, 2009 at 10:09 AM, Neeraj Jhawar <navderm at gmail.com> wrote:
>
> Respected Sir,
>
>
>
> Could you give me some reference as to how I communicate using events
> between the threads.
>
> Any material or some link.
>
>
>
> Thanks a lot.
>
>
>
> On Sat, Jan 10, 2009 at 8:22 AM, Andreas Pakulat <apaku at gmx.de> wrote:
>
> On 10.01.09 04:39:39, Neeraj Jhawar wrote:
> > Is there any way this problem of cross thread signal slot model can be
> done
> > in QT3?
>
> No, Qt3 doesn't support cross-thread signals/slots. You have to use event's
> in Qt3 to communicate between Threads.
>
>
> > Am really apprehensive of using QT4 after everything has been done...
>
> I suggest you really consider switching to Qt4 (not instantly, but starting
> to do so), Qt3 is not maintained anymore. Qt Software doesn't support it
> anymore since quite some time already.
>
> Andreas
>
> --
> You will experience a strong urge to do good; but it will pass.
>
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>
>
>
>   --
>
> Neeraj Jhawar
> Senior Undergraduate
> Mechanical Engineering Department
> Punjab Engineering College
> Chandigarh.
> India
>
>
>
>
> --
> Neeraj Jhawar
> Senior Undergraduate
> Mechanical Engineering Department
> Punjab Engineering College
> Chandigarh.
> India
>
>
>
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-- 
Neeraj Jhawar
Senior Undergraduate
Mechanical Engineering Department
Punjab Engineering College
Chandigarh.
India
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