Issue emitting signal from background thread.

[high_flyer]

show your code.
It seems 'LCD' is null.

[Chris@Link]

Start a new thread and run the worker_thread()

QThread *settingsFileUpdaterThread = new QThread;
settings_agent.moveToThread(settingsFileUpdaterThread);
settingsFileUpdaterThread->start();
QMetaObject::invokeMethod(&settings_agent, "worker_thread", Qt::QueuedConnection);

QThread *settingsFileUpdaterThread = new QThread;
settings_agent.moveToThread(settingsFileUpdaterThread);
settingsFileUpdaterThread->start();
QMetaObject::invokeMethod(&settings_agent, "worker_thread", Qt::QueuedConnection);

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void SettingsFileRetrievalAgent::worker_thread()
{
  while(1)
      status = updateSettingsIfPossible();
 
     if (status == RETURN_SUCCESS_CACHE_UPDATED)
     {
         emit updatedSettingsNotification(); //segfault
     }
     for( int count = 0; count < 2; ++count )
       sleep( 1 );
  }
}

void SettingsFileRetrievalAgent::worker_thread()
{
  while(1)
      status = updateSettingsIfPossible();

     if (status == RETURN_SUCCESS_CACHE_UPDATED)
     {
         emit updatedSettingsNotification(); //segfault
     }
     for( int count = 0; count < 2; ++count )
       sleep( 1 );
  }
}

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I have other threads that are just about identical and they don't seem to have a problem when emitting a signal.

[high_flyer]

Right.
Where did you initialize 'LCD'?

[Chris@Link]

MainWindow::MainWindow(QWidget *parent) :
  QMainWindow(parent),
  ui(new Ui::MainWindow)
{
  ui->setupUi(this);
  QMetaObject::invokeMethod(this, "startup" , Qt::QueuedConnection);
}

MainWindow::MainWindow(QWidget *parent) :
  QMainWindow(parent),
  ui(new Ui::MainWindow)
{
  ui->setupUi(this);
  QMetaObject::invokeMethod(this, "startup" , Qt::QueuedConnection);
}

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void MainWindow::startup()
      // Get pointer to layout manager for main window
      QLayout* layout = this->layout();
      // Add LCD screen to the main window layout at specified position
      LCD = new(IPR5000_LCD)(this);
      LCD->setGeometry(430,50,320,240);
      LCD->setParent(this);
      layout->addWidget(LCD);
}

void MainWindow::startup()
      // Get pointer to layout manager for main window
      QLayout* layout = this->layout();
      // Add LCD screen to the main window layout at specified position
      LCD = new(IPR5000_LCD)(this);
      LCD->setGeometry(430,50,320,240);
      LCD->setParent(this);
      layout->addWidget(LCD);
}

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[high_flyer]

does this initialization happen before you start settingsFileUpdaterThread ?
If so, what exactly "restaring()" does?
Sound like a place where all kind of mischief can happen, if "restarting()" is re-spawning threads or similar thread related stuff - if this is the case - care has to be taken that things are all correctly terminated and initialized.
If you comment out all the content of "restarting()" does it still crash (the same way)?

[Chris@Link]

void MainWindow::startup()
      // Get pointer to layout manager for main window
      QLayout* layout = this->layout();
      // Add LCD screen to the main window layout at specified position
      LCD = new(IPR5000_LCD)(this);
      LCD->setGeometry(430,50,320,240);
      LCD->setParent(this);
      layout->addWidget(LCD);
 
      KeyManagementAgent key_management_agent;
      SettingsFileRetrievalAgent settings_agent( key_management_agent );
      connect(&settings_agent, SIGNAL(updateSettingsNotification()), LCD, SLOT(restarting()));
      // move it to its own thread and do stuff with it.
     QThread *settingsFileUpdaterThread = new QThread;
     settings_agent.moveToThread(settingsFileUpdaterThread);
     settingsFileUpdaterThread->start();
     QMetaObject::invokeMethod(&settings_agent, "worker_thread", Qt::QueuedConnection);
 
}

void MainWindow::startup()
      // Get pointer to layout manager for main window
      QLayout* layout = this->layout();
      // Add LCD screen to the main window layout at specified position
      LCD = new(IPR5000_LCD)(this);
      LCD->setGeometry(430,50,320,240);
      LCD->setParent(this);
      layout->addWidget(LCD);

      KeyManagementAgent key_management_agent;
      SettingsFileRetrievalAgent settings_agent( key_management_agent );
      connect(&settings_agent, SIGNAL(updateSettingsNotification()), LCD, SLOT(restarting()));
      // move it to its own thread and do stuff with it.
     QThread *settingsFileUpdaterThread = new QThread;
     settings_agent.moveToThread(settingsFileUpdaterThread);
     settingsFileUpdaterThread->start();
     QMetaObject::invokeMethod(&settings_agent, "worker_thread", Qt::QueuedConnection);

}

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void IPR5000_LCD::restarting()
{
  ui->stackedWidget->setCurrentIndex(2);
}

void IPR5000_LCD::restarting()
{
  ui->stackedWidget->setCurrentIndex(2);
}

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Like I said previously I do this sort of thing other places without problems so I don't see any reason there would be a problem with the 'LCD', it just happens to be this thread that is giving me issues.

Commenting out the code in the restarting() method still results in a segfault. I tried printing a simple debug message and it still crashes. I don't think it's a problem with the LCD class. The LCD slot is never called because the signal is never emitted, that's how I know it cant be the LCD.

Edit: It will loop about 5-8 times before it throws a segfault.

I really appreciate the help.

[high_flyer]

1. Is 'key_management_agent' a parent for 'settings_agent' or just a parameter?
2. settings_agent is a stack variable, which dies at the end of the constructor. I would expect moveToThread() to have a problem with that - try allocating it on the heap.
This would also explain this==NULL.

Like I said previously I do this sort of thing other places without problems so I don't see any reason there would be a problem with the 'LCD', it just happens to be this thread that is giving me issues.

1.LCD was a likely candidate - since I don't know your code I wanted to rule it out.
2.I fail to see the relevance of the claim that something worked somewhere else since obviously its not *exactly* the same, and secondly, obviously it doesn't work here - so it helps little that it does somewhere else.
Specially when threads are in question - since alone different hardware (same software) may produce different results, or bring bugs to the surface on one system that are not see on another.
For your own good - stop thinking "this has to work" if it doesn't - rather "I must be doing something wrong if it doesn't work".
By the way, the code as you posted it, really requires no threads.

[Chris@Link]

1. Is 'key_management_agent' a parent for 'settings_agent' or just a parameter?
2. settings_agent is a stack variable, which dies at the end of the constructor. I would expect moveToThread() to have a problem with that - try allocating it on the heap.
This would also explain this==NULL.

Upon further investigation the settings_agent and the key_management_agent was being destroyed after we finished the startup function. I don't know how I managed to overlook that but I did.

2.I fail to see the relevance of the claim that something worked somewhere else since obviously its not *exactly* the same, and secondly, obviously it doesn't work here - so it helps little that it does somewhere else.
Specially when threads are in question - since alone different hardware (same software) may produce different results, or bring bugs to the surface on one system that are not see on another.
For your own good - stop thinking "this has to work" if it doesn't - rather "I must be doing something wrong if it doesn't work".
By the way, the code as you posted it, really requires no threads.

I understand, I was extremely frustrated and I overlooked the fact that the stack variable was being destroyed.


Thanks for the help.