How to run a task(particular function) independently without blocking my normal flow of code.

[HimanshuKaushik]

Hello Guys, I am working on project where I need to Update GUI every 100 ms based on signals I'm getting from controller. In this I need to download a Log file which is present in my controller. I am getting that file using ftp(Qnetworkaccessmanager). I am able to do these task separately. But when I combine it together my UI freezes till the file is downloaded.

I want my UI to update every 100 ms and also want log file to download in background. Please suggest any method.

while searching on Google I found that I can use Qthread to run it independently. so I have tried one example where I run a counter(increment by 1) every 1 sec and I have download button which triggers my thread and downloads the file. But still the counter(UI) freezes till the complete file is downloaded and then continues to increment by 2 which I dont know whys its happening.

I will pasted the whole code down so that u guys can help me figure how to run task independently without waiting for one task.
I am not expert so there might me logic error or something please feel free to suggest them too.

Code:
Project Name : test5
All Header files

mythread.h

#ifndef MYTHREAD_H
#define MYTHREAD_H

#include <QThread>
#include <QMutex>


class MyThread : public QThread
{
   Q_OBJECT

public slots:
    void stopRunning();

protected:
   virtual void run();

signals:
//   void signalValueUpdated(QString);

private:
    bool isRunning;

};




#endif // MYTHREAD_H

qftpfiledownload.h

#ifndef QFTPFILEDOWNLOAD_H
#define QFTPFILEDOWNLOAD_H

//HK 29/3/22
#include<qobject.h>
#include<QUrl>
#include<QtNetwork/QNetworkAccessManager>
#include<QtNetwork/QNetworkRequest>
#include<QtNetwork/QNetworkReply>
#include<QEventLoop>

class QftpFileDownload
{
public:
//    QNetworkReply *reply;   //HK 29/3/22
  QftpFileDownload(QString QftpPathName = "",QString QftpUserName = "", QString QftpPassword = "", QString QftpOutputName ="");
//    QNetworkAccessManager *nam;
//    QEventLoop loop;
  QString getPathName();
  QString getUserName();
  QString getPassword();
  QString getOutputName();
  void File_Download();
private:
    QString QftpPathName;   //HK 30/3/22 This requires full path with textfile name eg ."ftp://169.254.10.102/test.txt"
    QString QftpUserName;
    QString QftpPassword;
    QString QftpOutputName;



};

#endif // QFTPFILEDOWNLOAD_H

test5.h

#ifndef TEST5_H
#define TEST5_H

#include <QMainWindow>
#include<QString>
#include<QTimer>
#include"mythread.h"

namespace Ui {
class test5;
}

class test5 : public QMainWindow
{
    Q_OBJECT

public:
    explicit test5(QWidget *parent = 0);
    ~test5();
 unsigned int counter = 0;
    void display_time();

private slots:
    void on_pushButton_clicked();
    void updateTimer();
signals:
    void download_button_clicked();

private:
    Ui::test5 *ui;
    QTimer *Timer;
    MyThread thread;
};

#endif // TEST5_H

All source files

main.cpp

#include "test5.h"
#include <QApplication>
#include"ui_test5.h"

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

    test5 w;
    w.show();



   return a.exec();
}

mythread.cpp

#include "mythread.h"
#include <QString>
#include"qftpfiledownload.h"

void MyThread::run()
{
    qDebug("Thread id inside run %d",*((int*)QThread::currentThreadId()));

   
    isRunning = 1;
    QftpFileDownload object("ftp://169.254.10.102/test_100mb.txt","Administrator","Nopass123","Mytesting100.txt");

    object.File_Download();



}

void MyThread::stopRunning()
{
    isRunning = 0;
}

qftpfiledownload.cpp

#include "qftpfiledownload.h"
//HK 29/3/22
#include<QUrl>
#include<QtNetwork/QNetworkAccessManager>
#include<QtNetwork/QNetworkRequest>
#include<QtNetwork/QNetworkReply>
#include<QEventLoop>
#include<QFile>

#include"test5.h"



QftpFileDownload::QftpFileDownload(QString QftpPathName, QString QftpUserName, QString QftpPassword, QString QftpOutputName)
{
    this->QftpPathName = QftpPathName;
    this->QftpUserName = QftpUserName;
    this->QftpPassword = QftpPassword;
    this->QftpOutputName = QftpOutputName;
}

QString QftpFileDownload::getPathName()
{
    return QftpPathName;
}

QString QftpFileDownload::getUserName()
{
    return QftpUserName;
}

QString QftpFileDownload::getPassword()
{
    return QftpPassword;
}

QString QftpFileDownload::getOutputName()
{
    return QftpOutputName;
}

void QftpFileDownload::File_Download()
{
    QEventLoop loop;

 QNetworkAccessManager *nam = new QNetworkAccessManager();
 QObject::connect(nam, &QNetworkAccessManager::finished, &loop, &QEventLoop::quit);
qDebug()<<"Inside Function";
test5 time;
time.display_time();
//    QUrl url2("ftp://169.254.10.102/test.txt");
 QUrl url2(QftpPathName);
//      url2.setPassword("Nopass123");
//      url2.setUserName("Administrator");
 url2.setPassword(QftpPassword);
 url2.setUserName(QftpUserName);
  QNetworkRequest req(url2);
  QNetworkReply *reply = nam->get(req);
  loop.exec();

  QFile file(QftpOutputName);
  file.open(QIODevice::WriteOnly | QIODevice::Text);
  QTextStream out(&file);
  out<< reply->readAll();
  file.close();
  reply->deleteLater();

  qDebug()<<"Last line";
  time.display_time();
}

test5.cpp

#include "test5.h"
#include "ui_test5.h"
#include"qftpfiledownload.h"
#include"time.h"
//#include"mythread.h"

test5::test5(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::test5)
{
    ui->setupUi(this);

    Timer = new QTimer();
    connect(Timer,SIGNAL(timeout()),this,SLOT(updateTimer()));
    Timer->start(1000);
    qDebug("Thread id %d",*((int*)QThread::currentThreadId()));

    //When the start button is pressed, invoke the start() method in the counter thread
    QObject::connect(this,SIGNAL(download_button_clicked()),&thread,SLOT(start()), Qt::QueuedConnection);

    //When the stop button is pressed, invoke the stop() method in the counter thread
    //QObject::connect(stopButton,SIGNAL(clicked()),&thread,SLOT(stopRunning()), Qt::QueuedConnection);

    //When the counter thread emits a signal saying its value has been updated, reflect that change in the lineEdit field.
    //QObject::connect(&thread,SIGNAL(signalValueUpdated(const QString&)),lineEdit,SLOT(setText(const QString&)), Qt::QueuedConnection);

//    if(counter % 1000 == 0)
//    {
//        ui->Counter->setText(QString(counter));
//        counter =0;
//    }
}

test5::~test5()
{
    delete ui;
}

void test5::on_pushButton_clicked()
{
//    QftpFileDownload object("ftp://169.254.10.102/test_100mb.txt","Administrator","Nopass123","Mytesting100.txt");

//    object.File_Download();
    emit download_button_clicked();
}

void test5::updateTimer()
{
    static unsigned int Counter=0;

    ui->Counter->setText(QString::number(Counter));
    Counter++;
}

void test5::display_time()
{
    time_t rawtime;
    struct tm * timeinfo;
    time(&rawtime);
    timeinfo = localtime( &rawtime);
    qDebug("%02d:%02d:%02d\n",timeinfo->tm_hour, timeinfo->tm_min, timeinfo->tm_sec);
//	char output[8];
//	sprintf(output,"%02d:%02d:%02d",timeinfo->tm_hour, timeinfo->tm_min, timeinfo->tm_sec);
//	printf("%s\t",output);
//	printf("%d\n",sizeof(output));


}

test5.ui

I will paste the pro file too so that u guys can copy this and workout on this project

test5.pro

#-------------------------------------------------
#
# Project created by QtCreator 2022-03-31T10:12:10
#
#-------------------------------------------------

QT       += core gui network

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

TARGET = test5
TEMPLATE = app

# The following define makes your compiler emit warnings if you use
# any feature of Qt which has been marked as deprecated (the exact warnings
# depend on your compiler). Please consult the documentation of the
# deprecated API in order to know how to port your code away from it.
DEFINES += QT_DEPRECATED_WARNINGS

# You can also make your code fail to compile if you use deprecated APIs.
# In order to do so, uncomment the following line.
# You can also select to disable deprecated APIs only up to a certain version of Qt.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0


SOURCES += \
        main.cpp \
        test5.cpp \
    qftpfiledownload.cpp \
    mythread.cpp

HEADERS += \
        test5.h \
    qftpfiledownload.h \
    mythread.h

FORMS += \
        test5.ui

Thanks in advance

[Pl45m4]

@HimanshuKaushik

In first place, why you need to have threads at all?
QNetworkAccessManager works asynchronous using signals and slots.

[HimanshuKaushik]

@Pl45m4 oh okay but then why is UI getting freeze while that process is on?? How do I resolve that?

[Pl45m4]

@HimanshuKaushik

Your whole code / structure is quite confusing. AFAICS there's no need to create a QThread derived class.
If you want to increment your counter once a download is finished, just connect to the finished signal.

You could check out this example:

• https://doc.qt.io/qt-5/qtnetwork-downloadmanager-example.html

and @VRonin 's reply here:

• https://forum.qt.io/topic/88097/downloading-file-from-ftp-server/10

[SGaist]

Hi,

You have:

loop.exec();

In your code which will block the execution until the loop exits.

As you were already told, don't do that.

[HimanshuKaushik]

@SGaist So when I remove that loop event and its

loop.exec()

. I am not able to download the file at all. I am getting empty file when removing
loop.exec()

[jsulm]

@HimanshuKaushik said in How to run a task(particular function) independently without blocking my normal flow of code.:

I am getting empty file when removing

Because you have to do a bit more than just removing loop.exec()!
You need to write the file when you get all the data.
Please take a look at available examples, there is even one for downloading data: https://doc.qt.io/qt-5/qtnetwork-downloadmanager-example.html