Question

I have an object that is derived from QThread and the class definition includes the Q_OBJECT macro. I created a timer within the thread so I can do some occasional checks while the thread is running; however, the timeout event is never occurring.

I’ve tried making the timer a singleshot as well, but no events are emitted.

Are events processed in a thread by default or do I need to do something else to have them processed?

Here’s the code for how I set up the thread and timers:

void MyClass::run( void ) 
{ 
    checkTimer_chA = new QTimer( this ); 

    qDebug() << connect( checkTimer_chA, SIGNAL( timeout() ), this, SLOT( timerExpiry_chA() ) ); 

    checkTimer_chA->start( 1000 ); 

    // prevent multiple, simultaneous starts 
    if( !isRunning ) 
    { 
        qDebug() << "Thread: MyClass::run"; 
        isRunning = true; 

        while( isRunning ) 
        { 
            getData(); 
            processData(); 
            yieldCurrentThread(); 
        } 
    } 

    checkTimer_chA->stop(); 

    delete checkTimer_chA; 
}


void DAQ::timerExpiry_chA( void )
{
    qDebug() << "timerExpiry_chA";
    checkTimer_chA->stop();
}

If I add QApplication::processEvents(); right before the call to yieldCurrentThread(); the timer works as expected. However, this seems wrong to me.

Answer 1

Threads do not have their own event loops unless you explicitly create event loops in them. See http://doc.qt.io/qt-5/threads-qobject.html#per-thread-event-loop for details.