QTimer not working in new project

[davethomaspilot]

I'm having trouble getting QTimer to work in a console (no GUI) application.

When I start the timer, it goes active, but never times out.

When I tried using the static QTimer::singleShot method, I get a runtime error:

QObject::startTimer: QTimer can only be used with threads started with QThread

I've tried explicitly using Qt::QueuedConnection for the connection to the slot that tries to start the timer, but that makes no difference (and I think that's the default anyway).

Maybe the signal that's connected to the slot that starts the timer is on a different thread than what instantiated the QObject. The signal is emitted from an interrupt handler registered by the wiringPiISR() function provided by the wiringPi package.

Here's the code:

powerControl.h

#ifndef POWERCONTROL_H
#define POWERCONTROL_H
#define GPIO3 5
#include <QObject>
#include <QTimer>
#include <QDebug>
 
class PowerControl : public QObject
{
 
    Q_OBJECT
public:
    explicit PowerControl(QObject *parent = 0);
 
    static PowerControl *getInstance() {return instance;}
 
    static void handleEdgeBoth(void);
 
    virtual void handleIrq(bool afterEdgeState);
    ~PowerControl();
 
private:
     static PowerControl *instance;
     QTimer debounceTimer;
     QTimer tapTimer;
     QTimer powerOffTimer;
     static unsigned long lastTime;
 
signals:
     void fallingEdge(void);
     void risingEdge(void);
     void buttonPushed(void);
     void tapDetected(void);
     void longPressDetected();
 
public slots:
private slots:
     void edgeDetected(bool);
     void bounceFinished(void) {qDebug() << "Bounce timeout";}
     void tapTimeout(void) {qDebug() << "tap timeout";}
 
 
#define DEBOUNCE_TIME 10
};
 
#endif // POWERCONTROL_H

#ifndef POWERCONTROL_H
#define POWERCONTROL_H
#define GPIO3 5
#include <QObject>
#include <QTimer>
#include <QDebug>

class PowerControl : public QObject
{

    Q_OBJECT
public:
    explicit PowerControl(QObject *parent = 0);

    static PowerControl *getInstance() {return instance;}

    static void handleEdgeBoth(void);

    virtual void handleIrq(bool afterEdgeState);
    ~PowerControl();

private:
     static PowerControl *instance;
     QTimer debounceTimer;
     QTimer tapTimer;
     QTimer powerOffTimer;
     static unsigned long lastTime;

signals:
     void fallingEdge(void);
     void risingEdge(void);
     void buttonPushed(void);
     void tapDetected(void);
     void longPressDetected();

public slots:
private slots:
     void edgeDetected(bool);
     void bounceFinished(void) {qDebug() << "Bounce timeout";}
     void tapTimeout(void) {qDebug() << "tap timeout";}


#define DEBOUNCE_TIME 10
};

#endif // POWERCONTROL_H

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powerControl.cpp

#include "powercontrol.h"
#include "wiringPi.h"
#include <QDebug>
 
PowerControl *PowerControl::instance;
unsigned long PowerControl::lastTime = 0;
 
PowerControl::PowerControl(QObject *parent) : QObject(parent)
{
    debounceTimer.setSingleShot(true);
    debounceTimer.setInterval(DEBOUNCE_TIME);
    tapTimer.setSingleShot(true);
    tapTimer.setInterval(1000);
    powerOffTimer.setSingleShot(true);
 
    wiringPiISR(3,INT_EDGE_BOTH,handleEdgeBoth);
    //wiringPiISR(3,INT_EDGE_RISING,handleEdgeRisingInterrupt);
 
    connect(&tapTimer,SIGNAL(timeout()),this,SLOT(tapTimeout(void)),Qt::QueuedConnection);
    instance=this;
}
void PowerControl::handleEdgeBoth()
{
    PowerControl *pc = getInstance();
    unsigned long now = millis();
    unsigned long elapsedTime = now - lastTime;
    lastTime = now;
 
 
    qDebug() << "Elapsed time =" << elapsedTime;
 
    if (elapsedTime < DEBOUNCE_TIME)
    {
 
        qDebug() << "key bounce detected\n";
        return;
    }
    else
        emit pc->edgeDetected(digitalRead(3));
 
 
 
}
void PowerControl::handleIrq(bool afterEdgeState)
{
    if (afterEdgeState)
        qDebug() << "Rising Edge Detected";
    else
        qDebug() << "Falling Edge Detected";
}
void PowerControl::edgeDetected(bool edge)
{
    if (edge)
    {
        qDebug() << "Rising Edge Detected";
        tapTimer.stop();
    }
    else
    {
        QTimer::singleShot(1000, this, SLOT(tapTimeout(void)));
 
        tapTimer.start();
        qDebug() << "Falling Edge Detected, timer isActive = " << tapTimer.isActive();
    }
}
 
PowerControl::~PowerControl()
{
 
}

#include "powercontrol.h"
#include "wiringPi.h"
#include <QDebug>

PowerControl *PowerControl::instance;
unsigned long PowerControl::lastTime = 0;

PowerControl::PowerControl(QObject *parent) : QObject(parent)
{
    debounceTimer.setSingleShot(true);
    debounceTimer.setInterval(DEBOUNCE_TIME);
    tapTimer.setSingleShot(true);
    tapTimer.setInterval(1000);
    powerOffTimer.setSingleShot(true);

    wiringPiISR(3,INT_EDGE_BOTH,handleEdgeBoth);
    //wiringPiISR(3,INT_EDGE_RISING,handleEdgeRisingInterrupt);

    connect(&tapTimer,SIGNAL(timeout()),this,SLOT(tapTimeout(void)),Qt::QueuedConnection);
    instance=this;
}
void PowerControl::handleEdgeBoth()
{
    PowerControl *pc = getInstance();
    unsigned long now = millis();
    unsigned long elapsedTime = now - lastTime;
    lastTime = now;


    qDebug() << "Elapsed time =" << elapsedTime;

    if (elapsedTime < DEBOUNCE_TIME)
    {

        qDebug() << "key bounce detected\n";
        return;
    }
    else
        emit pc->edgeDetected(digitalRead(3));



}
void PowerControl::handleIrq(bool afterEdgeState)
{
    if (afterEdgeState)
        qDebug() << "Rising Edge Detected";
    else
        qDebug() << "Falling Edge Detected";
}
void PowerControl::edgeDetected(bool edge)
{
    if (edge)
    {
        qDebug() << "Rising Edge Detected";
        tapTimer.stop();
    }
    else
    {
        QTimer::singleShot(1000, this, SLOT(tapTimeout(void)));

        tapTimer.start();
        qDebug() << "Falling Edge Detected, timer isActive = " << tapTimer.isActive();
    }
}

PowerControl::~PowerControl()
{

}

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Hardware is Rpi Zero W, Qt 4.8 running on Stretch Lite

Thanks!

[d_stranz]

First comment - if you want PowerControl to be a Singleton, you need to make the constructor and destructor private. Otherwise, anyone can create a new, separate instance of PowerControl simply by using operator new(). And anyone could delete your "instance" simply by calling operator delete() on it, leaving you with a dangling pointer to a deleted object.

You haven't shown how you are using this class, but my hunch is that you are starting the timer before you have an event loop running (that is, before QApplication::exec() has been called in main()).

[davethomaspilot]

Thanks for the reply!

Yes, you are correct about the Singleton. It's ok to be a bit "sloppy" on this project , since it's so simple and I'm the only one who's ever going to work on it. That's my "excuse", but still, there's no reason not to do as you suggest!

No, the timer doesn't get started before exec is called. It gets started in the "edgeDetected" slot, which gets called as a result of an signal being emitted in the interrupt handler. And, the handler only gets called when I push a hardware button.

Here's the main.c (and that's ALL the code):

#include <QCoreApplication>


#include "powercontrol.h"
#include "ledcontrol.h"

int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);

//QApplication a(argc, argv);

a.setOrganizationName("Flying Nerd");
a.setApplicationName("Ipad2GMA");

wiringPiSetupSys();
PowerControl pc;
//LedControl *lc = new LedControl(1000,1000,2,true);


return a.exec();
}

[ChrisW67]

If the interrupt fires (expected or unexpected) between line 16 and 19 while your constructor is executing then you can be starting the timer before the event loop is running. At that time, instance will be uninitialized to boot.

Exactly what debugging output, if any, do you see?