How to run a QProcess in QThread without destroying the QThread

Hello! I don't get how to run a QProcess with QThread. Please help me, I tried also with both worker class and run() method but it doesn't work. I get: "QThread: desztroyed while thread is still running".
Here is my code:

mainwindow.h

Code:

---

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
 
#include <QWidget>
class mainWindow : public QWidget
{
    Q_OBJECT
    //here are defined some variables
 public:
    mainWindow(QWidget *parent = 0);
    ~mainWindow();
    void createUI();
    void process();
};
#endif // MAINWINDOW_H

---

mainwindow.cpp

Code:

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#include <QWidget>
#include <QPushButton>
#include <QProcess>
#include <QByteArray>
#include <QTextCodec>
#include <QString>
#include <QDebug>
#include "mainwindow.h"
 
mainWindow::mainWindow(QWidget *parent) : QWidget(parent)
{
    createUI();
}
 
 
mainWindow::~mainWindow()
{
 
}
void mainWindow::createUI(){
    //here I create the look of the window
     QPushButton buttonsearch = new QPushButton("Start process", this);
     buttonsearch->setToolTip("Start process");
     buttonsearch->setGeometry(200, 290, 100, 30);
     connect(buttonsearch, &QPushButton::clicked, [this]() {process(); });
}
 
void mainWindow::process(){
    process->setProcessChannelMode(QProcess::MergedChannels);
    process->start("\"D:\\YTDownloader\\youtube-dl.exe\" -e --no-playlist https://www.youtube.com/watch?v=6V-wwfuxZxw");
    process->waitForReadyRead();
    QByteArray a = process->readAllStandardOutput();
    QTextCodec* utfCodec = QTextCodec::codecForName("UTF-8");
    QString processStdout = utfCodec->toUnicode(a);
    qDebug() << processStdout;
}

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main.cpp

Code:

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#include <QApplication>
#include "mainwindow.h"
 
int main(int argl,char *argv[])
{
    QApplication app(argl,argv);
 
    mainWindow *window = new mainWindow();
    window->setWindowTitle("Test");
    window->setFixedSize(700, 335);
    window->show();
 
    return app.exec();
}

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I try to run process() function into a thread when buttonsearch is clicked. Thank you for your help!

Why do you want to run QProcess with QThread? The former starts a new process, you don't need a thread for that.

Quote:

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Originally Posted by wysota

Why do you want to run QProcess with QThread?

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The example code does not use QThread and I think the OP is confusing a thread (managed by QThread) with another process (managed by QProcess)

There seems to be an expectation that waitForReadyRead() does not return until all the process output is available: the call does not work like that, it returns when any of the process output is available. The code needs to either be reworked for a blocking mode of operation or to handle the output as it arrives between the start() call and the termination of the sub-process with slots connected to readyRead() etc. I suspect the latter option is better for a long-running download (like the example) while keeping a responsive UI.

Perhaps INeedADollar can tell us more about the problem.

Thanks for your response! I need the process in a thread because the window become unresponsive when I start the process.

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Added after 6 minutes:

Thanks for your response! I didn't add the thread part because it's something bad in it and I thought someone can show me how to do it right but if you want I send you that part. I need to run the process in a thread because window become unresponsive when I start the process. In my example I try to get the title of videos from YouTube and I will also need a thread to download them, but I will do the download part later.

I solved it! Thank you for your response. Below is the code if someone is interested:
mainwindow.h

Code:

---

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
 
#include <QWidget>
class mainWindow : public QWidget
{
    Q_OBJECT
    //here are defined some variables
 public:
    mainWindow(QWidget *parent = 0);
    ~mainWindow();
    void createUI();
    void process();
    QProcess *process = new QProcess(this);
 
private slots:
    void ReadOutput(int, QProcess::ExitStatus);
 
};
#endif // MAINWINDOW_H

---

mainwindow.cpp

Code:

---

#include <QWidget>
#include <QPushButton>
#include <QProcess>
#include <QByteArray>
#include <QTextCodec>
#include <QString>
#include <QDebug>
#include "mainwindow.h"
 
mainWindow::mainWindow(QWidget *parent) : QWidget(parent)
{
    createUI();
    connect(process, SIGNAL(finished(int, QProcess::ExitStatus)), this, SLOT(ReadOutput(int, QProcess::ExitStatus)));
}
 
 
mainWindow::~mainWindow()
{
 
}
void mainWindow::createUI(){
    //here I create the look of the window
     QPushButton buttonsearch = new QPushButton("Start process", this);
     buttonsearch->setToolTip("Start process");
     buttonsearch->setGeometry(200, 290, 100, 30);
     connect(buttonsearch, &QPushButton::clicked, [this]() {process(); });
}
 
void mainWindow::process(){
    process->setProcessChannelMode(QProcess::MergedChannels);
    process->start("\"D:\\YTDownloader\\youtube-dl.exe\" -e --no-playlist https://www.youtube.com/watch?v=6V-wwfuxZxw");
 
void readOutput(int exitCode, QProcess::ExitStatus exitStatus){
    qDebug() << exitCode;
    qDebug() << exitStatus;
    QByteArray a = process->readAllStandardOutput();
    QTextCodec* utfCodec = QTextCodec::codecForName("UTF-8");
    processStdout = utfCodec->toUnicode(a);
    qDebug() << processStdout;
}

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main.cpp

Code:

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#include <QApplication>
#include "mainwindow.h"
 
int main(int argl,char *argv[])
{
    QApplication app(argl,argv);
 
    mainWindow *window = new mainWindow();
    window->setWindowTitle("Test");
    window->setFixedSize(700, 335);
    window->show();
 
    return app.exec();
}

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You don't have a thread here, you know...

Yes I know. I don't need the thread I was wrong.

In your original code your UI became unresponsive because you blocked the main thread in waitForReadyRead()

In Qt most I/O is asynchronous for the very purpose of not blocking the main thread :)

Also, you don't need a lambda here

Code:

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connect(buttonsearch, &QPushButton::clicked, [this]() {process(); });

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you can directly connect to the process() function

Code:

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connect(buttonsearch, &QPushButton::clicked, this, &mainWindow::process);

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Cheers,
_