[Paraview] Plugin with own thread

Thu Mar 10 11:14:24 EST 2011

I replied prematurely without realizing the currentThreadId() is a
static method. So have you changed the "connect" to use a queued
connection or not?

Utkarsh

On Thu, Mar 10, 2011 at 8:05 AM, Utkarsh Ayachit
<utkarsh.ayachit at kitware.com> wrote:
> 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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>>
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>