Deferred function call using QTimer.

[Helg1980]

Hi!

I wrote code to implement a deferred function call using QTimer, but I still have one question: is there a possible error when the program can try to set the _repeat variable to '0' and execute_repeat++ at the same time?

#include <QTimer>
#include <iostream>
#include "preset.h"
#include "ui_preset.h"

int _repeat;

Preset::Preset(QWidget *parent) :
    QDialog(parent),
    ui_preset(new Ui::Preset)
{
    ui_preset->setupUi(this);
    QTimer::singleShot(1000, this, SLOT(repeat_handler()));
}

Preset::~Preset()
{
    delete ui_preset;
}

void Preset::on_comboBox_height_editTextChanged()  // Signal editText changed
{
    delay_function();
}

void Preset::delay_function()  // Delay function
{
    _repeat++;
    std::cout << "Repeat count: " << _repeat << std::endl;
}

void Preset::repeat_handler()  // Repeat handler
{
    if (_repeat > 0) {  // This is where the global variable checks whether there were calls delay_function
        _repeat = 0;
        change_preset_name();
    };
    QTimer::singleShot(1000, this, SLOT(repeat_handler())); //Re-enabling the timer to cyclical call the function repeat_handler
};

void Preset::change_preset_name()  // Call Change preset name
{
   // Change preset name
}

[JonB]

@Helg1980
No, signals/slots, timers and input signals all execute in sequence. There are no multiple threads here.

You don't have to keep invoking QTimer::singleShot(). If you want a regular timer, as your code does, use a repeating QTimer instance.

[Helg1980]

Thanks!
Used the construction :

QTimer *timer = new QTimer(this);
timer->setInterval(1000);
connect(timer, SIGNAL(timeout()), this, SLOT(repeat_handler()));
timer->start();

[JonB]

@Helg1980
This is good.

If you QTimer *timer = new QTimer() you'll need to delete it when no longer needed/the Preset instance is destructed. If you want one QTimer throughout a Preset, which is what it looks like, you can just have a member QTimer timer (not pointer) and you don't have to worry about leak/scope.

[SGaist]

@JonB see:

@Helg1980 said in Deferred function call using QTimer.:

QTimer *timer = new QTimer(this);

The QTimer object has a parent so it will be deleted through the parent child system.

However, it won't be easily manipulated if that is needed.

[JonB]

@SGaist , @Helg1980
Sorry, you can see from what I wrote I just missed the this parameter. My bad.