The most accurate timer qt C++

Question

I use QTimer to send periodically \'Ping\' packet to the server (MQTT client). But it timer is not absolutely accurate. After some time of working it has some delay and server b

Answer 1

#pragma once

#include <cstdint>
#include <QObject>

class PrecisePolling : public QObject
{
    Q_OBJECT
private:
    std::uint64_t previousPollingTime;
public:
    PrecisePolling();

public slots:
    void doPolling();

---

#include "precisepolling.h"
#include "QDateTime"
#include <QDebug>

PrecisePolling::PrecisePolling()
    : previousPollingTime(QDateTime::currentMSecsSinceEpoch())
{}

void PrecisePolling::doPolling()
{
    const std::uint64_t ms = QDateTime::currentMSecsSinceEpoch();
    qDebug() << ms - previousPollingTime;
    previousPollingTime = ms;
}

---

#include <QCoreApplication>
#include <QThread>
#include <QTimer>
#include "precisepolling.h"

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

    QThread thread;
    QTimer timer;
    PrecisePolling pp;

    timer.setInterval(1000);
    timer.setTimerType(Qt::PreciseTimer);

    QObject::connect(&timer, &QTimer::timeout, &pp, &PrecisePolling::doPolling);
    timer.start();
    timer.moveToThread(&thread);
    pp.moveToThread(&thread);

    thread.start(QThread::Priority::TimeCriticalPriority);

    return a.exec();
}

Answer 2

Run a QTimer on a separate QThread which doesn't do anything else. If you're running the timer on an already busy thread the timeout events may not come on time or not at all.

Make a worker class e.g. "PingPacketWorker", implement a slot that does pinging. Make a QThread. Connect your QTimer and PingPacketWorker signal/slots. Start the timer. Call moveToThread on the PingPacketWorker and the QTimer, the timer should restart because of moveToThread, note you can only start / stop it on the owner thread!

You could also increase your QThread's priority since you asked for "the most accurate" solution ...

Update:

Also, set QTimer::setTimerType(Qt::PreciseTimer)

The default Qt::CoarseTimer is less precise (5% of the interval)