My program crashes if QProcess is restarted directly when it has finished

[norobro]

Apparently notRunning != finished(). On Linux I get the following warning on the command line:

QSocketNotifier: Multiple socket notifiers for same socket 15 and type Read

Try the following code:

#include <QCoreApplication>
#include <QProcess>
#include <QDebug>
#include <QTimer>
 
class process_handler : public QObject
{
    Q_OBJECT
public:
    process_handler() {
        connect(&p, SIGNAL(stateChanged(QProcess::ProcessState)), this, SLOT(process_state_changed(QProcess::ProcessState)));
        connect(&p, SIGNAL(finished(int, QProcess::ExitStatus)), this, SLOT(process_finished(int, QProcess::ExitStatus)));
        start_process();
    }
public slots:
    void process_state_changed(QProcess::ProcessState state) {
        if (state == QProcess::Starting)
            qDebug() << "Process is starting up...";
        if (state == QProcess::Running)
            qDebug() << "Process is now running." ;
        if (state == QProcess::NotRunning){
            qDebug() << "Process is finished running.";
            start_process();
            //QTimer::singleShot(0, this, SLOT(start_process()));
        }
    }
    void process_finished(int  , QProcess::ExitStatus ){
        qDebug() << "received finished signal";
    }
    void start_process() {
        p.start("ping 1.1.1.1 -c 1 -W 3");  // from your previous thread
    }
private:
    QProcess p;
};
 
int main(int argc, char *argv[]) {
    QCoreApplication app(argc, argv);
    process_handler ph;
    app.exec();
}
#include "main.moc"

#include <QCoreApplication>
#include <QProcess>
#include <QDebug>
#include <QTimer>

class process_handler : public QObject
{
    Q_OBJECT
public:
    process_handler() {
        connect(&p, SIGNAL(stateChanged(QProcess::ProcessState)), this, SLOT(process_state_changed(QProcess::ProcessState)));
        connect(&p, SIGNAL(finished(int, QProcess::ExitStatus)), this, SLOT(process_finished(int, QProcess::ExitStatus)));
        start_process();
    }
public slots:
    void process_state_changed(QProcess::ProcessState state) {
        if (state == QProcess::Starting)
            qDebug() << "Process is starting up...";
        if (state == QProcess::Running)
            qDebug() << "Process is now running." ;
        if (state == QProcess::NotRunning){
            qDebug() << "Process is finished running.";
            start_process();
            //QTimer::singleShot(0, this, SLOT(start_process()));
        }
    }
    void process_finished(int  , QProcess::ExitStatus ){
        qDebug() << "received finished signal";
    }
    void start_process() {
        p.start("ping 1.1.1.1 -c 1 -W 3");  // from your previous thread
    }
private:
    QProcess p;
};

int main(int argc, char *argv[]) {
    QCoreApplication app(argc, argv);
    process_handler ph;
    app.exec();
}
#include "main.moc"

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The output on my box is:

Process is starting up...
Process is now running.
Process is finished running.
QSocketNotifier: Multiple socket notifiers for same socket 15 and type Read
Process is starting up...
received finished signal

I haven't looked at the source code but what appears to happen is the new process assigns a QSocketNotifier to the same
socket as the old process and the old process deletes the socket. My app just idles in the event loop after the output
above. Maybe Windows segfaults?