[Paraview] Plugin with own thread

[Utkarsh Ayachit]

If you look at http://doc.qt.nokia.com/latest/qobject.html#thread

you'll see that QObject::thread() returns the thread to which the
object belongs, not the thread in which the code is being executed.

Utkarsh

On Thu, Mar 10, 2011 at 12:35 AM, Stephan Rogge
<Stephan.Rogge at tu-cottbus.de> wrote:
> Hello Utkarsh,
>
> thank you very much for the quick response and thanks for pointing me
> on the QThread documentation. Regarding to the QT doc I realized a
> direct connection here, which leads to an immediately processing of
> Trigger().
>
> Well, my assumption was indeed wrong. So I went back to my code and
> include some debug outputs to clarify which thread processes the
> pqMyApplicationStarter::Trigger() method. In order to get these
> information I output the current thread Ids of my plugin (in
> onStartup and Trigger) ...
>
>        void pqMyApplicationStarter::onStartup()
>        {
>                ...
>                qWarning() << "Message from pqMyApplicationStarter:
>                        Application Started
>                        (" << this->thread()->currentThreadId() << ")";
>
>        }
>
>        void pqMyApplicationStarter:: Trigger()
>        {
>                ...
>                qWarning() << "pqMyApplicationStarter::Trigger():
>                        " <<  this->thread()->currentThreadId();
>
>        }
>
> and in my external thread (Thread::run).
>
>        void Thread::run()
>        {
>                running = true;
>
>                while( running )
>                {
>                        qWarning() << "Thread::run(): " <<
> currentThreadId();
>
>                        // Fire the signal
>                        emit UpdatedData();
>
>                        qWarning() << "Invocation done";
>                }
>        }
>
> This lead to the following output:
>
>        Message from pqMyApplicationStarter: Application Started ( 0x1514 )
>        Thread::run():                      0x123c
>        pqMyApplicationStarter::Trigger():  0x1514
>        Invocation done
>
> And here I a new question arises: It seems to be, that Trigger is
> invoked in my external thread and waits for return but is processed
> in the plugin thread. Is that right?
>
>
> Thanks again,
>
> Best regards,
> Stephan
>
>
> -----Ursprüngliche Nachricht-----
> Von: Utkarsh Ayachit [mailto:utkarsh.ayachit at kitware.com]
> Gesendet: Mittwoch, 9. März 2011 17:25
> An: Stephan Rogge
> Cc: paraview at paraview.org
> Betreff: Re: [Paraview] Plugin with own thread
>
> You might want to read
> http://doc.qt.nokia.com/latest/threads-qobject.html especially the
> section about signal/slots and threads.
>
> In your code, contrary to what you expect, Trigger() is being called
> in your thread and not the "main thread" and hence the issues you
> might be seeing. If you simply change the connection to use a
> Qt::QueuedConnection you'd get the desired effect.
>
> Utkarsh
>
> On Wed, Mar 9, 2011 at 8:10 AM, Stephan Rogge
> <Stephan.Rogge at tu-cottbus.de> wrote:
>> Hello,
>>
>>
>>
>> after reading the tutorials and How-to’s for writing ParaView Plugins I’ve
>> started with the Autostart-Example project. My goal was to create a plugin
>> which is executed in an external thread. It might happens that I need this
>> in the near future.
>>
>>
>>
>> Well, it works quit well, I guess. But to avoid some errors and
>> miss-behaviors I need a confirmation that I am on the right way.
>>
>>
>>
>> My approach is to use the signal-slot-pattern to communicate between the
>> main thread of ParaView and my own plugin-thread. The class
>> pqMyApplicationStarter represents the ParaView-plugin (which is running in
>> the main thread of ParaView?). There is an object in this class which
>> executes a loop within an external thread ( class Thread ), which extends
>> QThread.
>>
>>
>>
>> As I read somewhere that vtk isn’t implemented threaded-safe at all (at
>> least the rendering stuff) I decided to do all render calls in
>> pqMyApplicationStarter. When the UpdatedData()signal is fired the active
>> view needs to re-rendered.
>>
>>
>>
>> The question I want to ask is very simple: Is this the right / best way to
>> create a thread and communicate with it via signals?
>>
>>
>>
>>
>>
>> /////////////// Thread.h ////////////////////////////
>>
>> class Thread : public QThread
>>
>> {
>>
>> Q_OBJECT
>>
>> public:
>>
>> Thread(QObject* parent = 0);
>>
>> virtual ~Thread();
>>
>> virtual void run();
>>
>> signals:
>>
>>       void UpdatedData();
>>
>> };
>>
>>
>>
>>
>>
>>
>>
>> void Thread::run()
>>
>> {
>>
>>       running = true;
>>
>>
>>
>>       while( running )
>>
>>       {
>>
>> // Sleep awhile
>>
>>             msleep( 800 );
>>
>>             // Fire the signal
>>
>>             emit UpdatedData();
>>
>>       }
>>
>> }
>>
>> /////////////////////////////////////////////////////
>>
>>
>>
>>
>>
>> /////////////// pqMyApplicationStarter //////////////
>>
>> class pqMyApplicationStarter : public QObject
>>
>> {
>>
>>       Q_OBJECT
>>
>>       typedef QObject Superclass;
>>
>>
>>
>> public:
>>
>>       pqMyApplicationStarter(QObject* p=0);
>>
>>       ~pqMyApplicationStarter();
>>
>>
>>
>>       // Callback for startup.
>>
>>       void onStartup();
>>
>>
>>
>> public slots:
>>
>>       void Trigger();
>>
>> };
>>
>>
>>
>>
>>
>>
>>
>> void pqMyApplicationStarter::onStartup()
>>
>> {
>>
>>       myThread = new Thread();
>>
>>       myThread->start();
>>
>>
>>
>>       pqActiveObjects::instance().connect( myThread,
> SIGNAL(UpdatedData()),
>> this, SLOT(Trigger()) );
>>
>> }
>>
>>
>>
>> void pqMyApplicationStarter::Trigger()
>>
>> {
>>
>>       pqActiveObjects* object = &(pqActiveObjects::instance());
>>
>>       pqView* view            = object->activeView();
>>
>>
>>
>>       if (view)
>>
>>       {
>>
>>             view->render();
>>
>>       }
>>
>>
>>
>>       view  = NULL;
>>
>> }
>>
>>
>>
>>
>>
>> Thanks a lot.
>>
>>
>>
>> Cheers,
>>
>> Stephan
>>
>>
>>
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