How to Stop a QThread That Runs a Blocking Forever Loop?

Question

I have some rough code that I've been experimenting with:

someserver.cpp (a GUI)

#include "server.h"
#include "ui_server.h"

Server::Server(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::Server)
{
    ui->setupUi(this);
}

Server::~Server()
{
    delete ui;
}

void Server::onBtnStartClicked()
{
    QThread worker; 
    worker.start(); // Start worker thread that goes into an infinite loop with a blocking call
}

void Server::onBtnExitClicked()
{
    // How do I cleanly stop worker from running?
    QApplication::quit();
}

worker.cpp

#include "worker.h"

Worker::Worker(QObject *parent) :
    QThread(parent)
{
}

void Worker::run()
{
    for (;;)
    {
        // a blocking IO call here like pipe, or msgrcv
        // process data received
    }
}

Since the worker thread runs in a forever loop with a blocking IO call, how will I be able to structure this so that when the Stop button is pressed in the GUI thread, the worker thread is stopped cleanly?

Answer 1

You could of course put a boolean value within the for loop in Worker::run() checked every iteration, which breaks on ==true and is set by the gui Stop button. Of course, this won't quit the thread while execution is blocked.

Probably better is to get rid of the for loop and use Qt's signals and slots to setup a callback function, connected to a signal like QIODevice::readyRead(). These will be called only when there is information available in the socket/pipe whatever. Any other time you'll be able to quit the thread with QThread::exit(). You'll need to call QThread::exec() at some point as well to get the event loop going.

Answer 2

in infinity loop paste this code and enjoy...

QTime dieTime = QTime::currentTime().addMSecs(1);
while( QTime::currentTime() < dieTime ) {
    QCoreApplication::processEvents( QEventLoop::AllEvents, 1);
}

don't forget

#include <QCoreApplication>

#include <QTime>

see you