[Qt-interest] qt event loop in a DLL for thread signal slot mechanism
Lars Friedrich Lars
lars-friedrich at gmx.net
Thu Nov 5 12:57:41 CET 2009
Hi cyril (?),
this was my first notion too, but then I did some experiments with the original code and recognized that it is simply not true that the example relies on QCoreApplication::exec(). However, it relies on the instantiation of a QCoreApplication-object, but this is no problem (at least for my situation).
In the concrete example of Bradley Hughes, consequently, we cannot use the line
app.connect(&producerThread, SIGNAL(finished()), SLOT(quit()));
anymore, but this is not important (at least not for my DLL-framework).
I attached the zip with my experimental changes to Bradley's source (I use CMake for building). I think this piece of code will show you, that we do not rely on running QCoreApplication::exec().
Hope that helps,
lars
-------- Original-Nachricht --------
> Datum: Thu, 05 Nov 2009 12:13:17 +0100
> Von: "cyril.mailing.list" <cyril.mailing.list at gmail.com>
> An: Lars Friedrich Lars <lars-friedrich at gmx.net>
> CC: Mike Jackson <imikejackson at gmail.com>, qt-interest at trolltech.com
> Betreff: Re: [Qt-interest] qt event loop in a DLL for thread signal slot mechanism
> Hi, I am also interested by the answer to that problem but I did not get
> it since the producer-consumer sample code written by Bradley Hughes
> still relies on instanciating and executing QCoreApplication...
> How did you work around that to solve your eventloop conflict ?
>
>
> Lars Friedrich Lars a écrit :
> > Hello Mike,
> >
> > thank you very much for your suggestion!
> > I modified the code of producerconsumer2.tar.gz a bit to simulate my
> needs and packed it into my DLL. Tests showed that this mechanism avoids the
> Qt event loops to 'eat' my key press events of the calling
> Delphi-application, and that is exactly what I need.
> > However, now I have to adapt my real code to conform to the suggested
> lines of code ...
> > Thank you again!
> >
> > regards,
> >
> > lars
> >
> > -------- Original-Nachricht --------
> >
> >> Datum: Wed, 4 Nov 2009 10:47:42 -0500
> >> Von: Mike Jackson <imikejackson at gmail.com>
> >> An: qt-interest at trolltech.com
> >> Betreff: Re: [Qt-interest] qt event loop in a DLL for thread signal
> slot mechanism
> >>
> >
> >
> >> I ran into something similar in the last few weeks. I was trying to
> >> send signals across threads and needed the event loop running in the
> >> thread.
> >>
> >> http://labs.trolltech.com/blogs/2007/07/05/qthreads-no-longer-abstract/
> >>
> >> http://chaos.troll.no/~bhughes/producerconsumer2.tar.gz
> >>
> >> That code more or less worked for what I wanted to do.
> >>
> >> Mike Jackson
> >>
> >>
> >> On 2009-11-04 02:23:00 -0500, "Lars Friedrich Lars"
> >> <lars-friedrich at gmx.net> said:
> >>
> >>
> >>> Hi Alex,
> >>>
> >>> unfortunately replacing QApplication by QCoreApplication does not fix
> >>> the problem. The behavior is exactly the same.
> >>>
> >>> regards,
> >>>
> >>> lars
> >>>
> >>> -------- Original-Nachricht --------
> >>>
> >>>> Datum: Tue, 3 Nov 2009 15:25:43 -0800
> >>>> Von: "Malyushytsky, Alex" <alex at wai.com>
> >>>> An: "qt-interest at trolltech.com" <qt-interest at trolltech.com>
> >>>> Betreff: Re: [Qt-interest] qt event loop in a DLL for thread
> >>>> signal slot mechanism
> >>>>
> >>>>>> - Why does the Qt event loop 'steal' the keypress events although
> it
> >>>>>>
> >> is
> >>
> >>>> not a GUI application?
> >>>>
> >>>> Never done what you are trying to do, but QApplications always means
> >>>>
> >> GUI
> >>
> >>>> related initialization.
> >>>> If you don't need GUI, try to use QCoreApplication instead and see if
> >>>>
> >> it
> >>
> >>>> solves your problem.
> >>>>
> >>>> Regards,
> >>>> Alex
> >>>>
> >>>> -----Original Message-----
> >>>> From: qt-interest-bounces at trolltech.com
> >>>> [mailto:qt-interest-bounces at trolltech.com] On Behalf Of Lars
> Friedrich
> >>>>
> >> Lars
> >>
> >>>> Sent: Tuesday, November 03, 2009 3:00 PM
> >>>> To: qt-interest at trolltech.com
> >>>> Subject: [Qt-interest] qt event loop in a DLL for thread signal slot
> >>>> mechanism
> >>>>
> >>>> Hello qt developers,
> >>>>
> >>>> I have some serious problems with Qt event loop's behavior when using
> >>>>
> >> it
> >>
> >>>> in a windows DLL as an interface for a Delphi5-application.
> >>>>
> >>>> I am wrapping some image conversion capabilities (furthermore using
> the
> >>>> open source toolkits ITK and VTK with cross-platform build tool
> CMake)
> >>>>
> >> in a
> >>
> >>>> DLL which incorporates Qt-threads. The DLL is more or less a tool
> which
> >>>>
> >> gets
> >>
> >>>> used by a Delphi5-application. The Delphi-application calls a
> function
> >>>>
> >> of
> >>
> >>>> the DLL which internally initiates a QThread which does some
> >>>>
> >> parametrized
> >>
> >>>> image conversion tasks in the background. In order to detect the end
> of
> >>>>
> >> a
> >>
> >>>> background thread I use QThread's finished()-signal and connect it to
> a
> >>>> DLL-internal slot which furthermore triggers a DLL-callback so that
> the
> >>>>
> >> calling
> >>
> >>>> Delphi-application gets notified as well.
> >>>> After some tests and studying the Qt-documentation, I noticed that I
> >>>>
> >> need
> >>
> >>>> an active Qt event loop within the DLL to make the signal/slot
> >>>>
> >> mechanism
> >>
> >>>> work. I decided to instantiate a DLL-global QApplication instance and
> >>>>
> >> call
> >>
> >>>> its (blocking!) exec()-method after loading the DLL internally. I
> >>>>
> >> implemented
> >>
> >>>> that by initiating a timer in the Delphi-application which calls the
> >>>> blocking (!!!) QApplication's exec()-mehod using the DLL (as I read
> in
> >>>>
> >> Qt's
> >>
> >>>> documentation that the event loop can only be started from the main
> >>>>
> >> thread!).
> >>
> >>>> However, that seems to work as the signal/slot mechanism seems to
> work
> >>>> correctly (I verified that with a log file).
> >>>>
> >>>> Now my problem: as soon as the Qt event loop is running it seems to
> >>>> seriously influence the Delphi-application's event loop (its GUI
> >>>>
> >> behavior):
> >>
> >>>> - Delphi's TApplication OnIdle event is no longer invoked (this
> problem
> >>>>
> >> is
> >>
> >>>> more or less solved because I can generate this event by myself using
> a
> >>>> timer and analyzing the message queue state)
> >>>> - (some essential but not all) keypress/keydown/keyup events of the
> >>>> Delphi-application's GUI seem to be 'stolen' by Qt's event loop -
> they
> >>>>
> >> do not
> >>
> >>>> arrive in the Delphi application (for example the tab-key is no
> longer
> >>>> recognized by the Delphi-application to navigate through its GUI's
> >>>>
> >> controls)
> >>
> >>>> Now, my qestions:
> >>>> - Did some of you tackle a similar problem?
> >>>> - Why does the Qt event loop 'steal' the keypress events although it
> is
> >>>> not a GUI application?
> >>>> - Can I 'pipe' the keypress events back to the Delphi-application's
> >>>>
> >> main
> >>
> >>>> thread (message queue)? Or could I connect the DLL's event loop
> >>>>
> >> directly to
> >>
> >>>> the Delphi-application's event loop?
> >>>> - Or did I completely misunderstand some Qt-fundamentals? Could I
> >>>> implement the signal/slot mechanism with some simpler Qt-tools than a
> >>>> QApplication?
> >>>> Maybe a lightweight event loop specific to thread signal/slot
> >>>>
> >> mechanism?
> >>
> >>>> Any comments on this issue are really really appreciated!!!
> >>>> Please help me.
> >>>>
> >>>> Thank you!!!!!!
> >>>>
> >>>>
> >>>> best regards,
> >>>>
> >>>> lars
> >>>>
> >>>> --
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> >>>> Jetzt freischalten unter http://portal.gmx.net/de/go/maxdome01
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