thread problem

[^NyAw^]

Hi,

I think that you have to use the thread to perform the heavy computation and let the main thread process events and update the GUI.
So, let the main thread perform the animation and the other thread to perform the heavy computation. If the thread needs to send some message to the main thread use the SIGNAL SLOT mechanism.
The thread that you have to code have not to have an event loop, it have to be something like this:

void myClassThread::run()
{
  while(!bFinish)
  {
     //Do some work
  }
  //It will exit "while" when "bFinish" is true, so then the "run" method will exit and so the thread will stop
}

void myClassThread::run()
{
  while(!bFinish)
  {
     //Do some work
  }
  //It will exit "while" when "bFinish" is true, so then the "run" method will exit and so the thread will stop
}

To copy to clipboard, switch view to plain text mode 

[Cruz]

I would also add a small sleep to the worker thread's event loop, so that it doesn't gobble all the cpu power and gives the main thread a chance to perform normally.

void myClassThread::run()
{
  while(!bFinish)
  {
     //Do some work
     msleep(10);
  }
  //It will exit "while" when "bFinish" is true, so then the "run" method will exit and so the thread will stop
}

void myClassThread::run()
{
  while(!bFinish)
  {
     //Do some work
     msleep(10);
  }
  //It will exit "while" when "bFinish" is true, so then the "run" method will exit and so the thread will stop
}

To copy to clipboard, switch view to plain text mode 

[^NyAw^]

Hi,

I would also add a small sleep to the worker thread's event loop, so that it doesn't gobble all the cpu power and gives the main thread a chance to perform normally.

You don't need this.
I have an application that contain 4 classes. Every class have 2 threads(heavy computation threads). The main thread responds perfectly to GUI events like mouse clicks, ...

Note that the main thread is a thread, so it will fight to obtain CPU time as the others threads do the same.
Think that maybe the main thread only needs a few "ticks" to perform its job.

And note that this approach is not using an "eventLoop" as you said.

[talk2amulya]

hi guys,

thanks for ur input, but i cant move the heavy processing code into a different thread cuz it involves many GUI operations is there ANY other way to do it like i did..what i dont understand is why qApp->processEvents() doesnt work out of a different thread..whereas it was working in the main thread.

[spirit]

create propper signal/slot approach for separating gui and non-gui operation. try to revise your havy-compution algorithm.

[^NyAw^]

Hi,

If the heavy computation performs GUI, use SIGNAL SLOT mechanism to let the main thread do the GUI operations. It's not difficult.

But if you really want to do it as you tell, why use a thread that starts a timer? Only start a timer on the main thread and try if the calls to "processEvents" work.

[talk2amulya]

looks like a revising in the heavy-computation algorithm is in order....a connect in the main also doesnt work..its really strange....thanks guys for ur time!

[^NyAw^]

Hi,

a connect in the main also doesnt work

Is "yourClassThread" defining the "Q_OBJECT" macro?

You can take a look at console output to see why it don't connect. Note that the connections have to be "Qt::QueuedConnection" or let it autodetect.

[talk2amulya]

i meant i cant use connect(...) in main() because where would i put Q_OBJECT?? about Qt::QueuedConnection , yes i used that too..still didnt work..i m sure if i get to call processEvents() at a certain interval until the processing is over, i can animate the icon..but for sm reason, none of my attempts to call processEvents(), either from main() or other thread is working....

[spirit]

create an object in main thread (in main.cpp) which will call qApp->processEvents by QTimer::timeOut.

....
class MyProcessEventDispatcher: public QObject
{
    Q_OBJECT
 
public:
       MyProcessEventDispatcher(QObject *parent = 0) 
          : QObject (parent) 
        {
                m_timer.setInterval(100);
                connect(&m_timer, SIGNAL(timeout()), SLOT(updateEvents()));
                m_timer.start();
       }
 
private slots:
      void updateEvents() 
      {
            m_timer.start();
            qApp->processEvents();
       }
private:
     QTimer m_timer;
};
#include "main.moc" 
int main(int argc, char **argv)
{
      QApplication app(argc, argv);
      MyProcessEventDispatcher mpee;
      ...  
      return app.exec();
}

....
class MyProcessEventDispatcher: public QObject
{
    Q_OBJECT

public:
       MyProcessEventDispatcher(QObject *parent = 0) 
          : QObject (parent) 
        {
                m_timer.setInterval(100);
                connect(&m_timer, SIGNAL(timeout()), SLOT(updateEvents()));
                m_timer.start();
       }

private slots:
      void updateEvents() 
      {
            m_timer.start();
            qApp->processEvents();
       }
private:
     QTimer m_timer;
};
#include "main.moc" 
int main(int argc, char **argv)
{
      QApplication app(argc, argv);
      MyProcessEventDispatcher mpee;
      ...  
      return app.exec();
}

To copy to clipboard, switch view to plain text mode 

[talk2amulya]

for some reason

connect(&m_timer, SIGNAL(timeout()), SLOT(updateEvents()));

connect(&m_timer, SIGNAL(timeout()), SLOT(updateEvents()));

To copy to clipboard, switch view to plain text mode 

isnt getting connected..

[spirit]

I've updated code and also tested it. a slot is called normal.

[talk2amulya]

yeh, i made those changes too but still updateEvents() is only getting called once, until whole of the processing is done..so no help from this either..thanks though, spirit...

[^NyAw^]

Hi,

#include <QThread>
class myThread : public QThread
{
  Q_OBJECT
public:
  //Redefine this method with your computation
  void run()
  {
     while(!bStop)
     {
       //Do some work
       emit (emitShowText(QString("Hello Thread"));
       ...
     }
 
  }
 
signals:
  void emitShowText(QString);            //Define all the signals you want to emit
  void emitShowProcessProgress(int);
}

#include <QThread>
class myThread : public QThread
{
  Q_OBJECT
public:
  //Redefine this method with your computation
  void run()
  {
     while(!bStop)
     {
       //Do some work
       emit (emitShowText(QString("Hello Thread"));
       ...
     }

  }

signals:
  void emitShowText(QString);            //Define all the signals you want to emit
  void emitShowProcessProgress(int);
}

To copy to clipboard, switch view to plain text mode 

myAppWindow::myAppWindow(QWidget *parent, Qt::WFlags flags) : QMainWindow(parent, flags)
{
  ui.setupUi(this);  //Setup UI if used a GUI editor like QDesigner
 
  //Create the thread and connect it's signals to "this" slots
  m_pThread = new myThread(this);
  bool bC = connect(m_pThread,SIGNAL(emitShowText(QString)),this,SLOT(showText(QString)),Qt::QueuedConnection); //Insert a debug point and take a look at console out. If connection fail it will reach error message on it
 
  m_pThread->start();  //Enter the Thread "run" method
}

myAppWindow::myAppWindow(QWidget *parent, Qt::WFlags flags) : QMainWindow(parent, flags)
{
  ui.setupUi(this);  //Setup UI if used a GUI editor like QDesigner

  //Create the thread and connect it's signals to "this" slots
  m_pThread = new myThread(this);
  bool bC = connect(m_pThread,SIGNAL(emitShowText(QString)),this,SLOT(showText(QString)),Qt::QueuedConnection); //Insert a debug point and take a look at console out. If connection fail it will reach error message on it

  m_pThread->start();  //Enter the Thread "run" method
}

To copy to clipboard, switch view to plain text mode