Exception is not catched in QThread

[qmmj]

Hi,
I'm trying to use the exiv2 library to modify image metadata. This library uses C++ exceptions. My code is working in the main thread ( e.g. in the constructor of the QThread ), but when I move it to the threads run() method I the exception does not get caught and the program crashes:

try {
    Exiv2::ImageFactory::open("C:\\Path_to\\invalid_file.tiff");
} catch ( ... ) {
    qDebug("got it!");
}

I'm using the MSVC2015 and Qt 5.9.1

[A Former User]

Hi! Just tested it on desktop Linux. Created a widgets projects, added a pushbutton to the mainwindow. And created a worker class for the thread:
worker.h

#ifndef WORKER_H
#define WORKER_H

#include <QObject>

class Worker : public QObject
{
    Q_OBJECT
public:
    Worker(QObject *parent = nullptr);
    ~Worker();
public slots:
    void process();
signals:
    void finished();
};

#endif // WORKER_H

worker.cpp

#include "worker.h"
#include <unistd.h>
#include <exiv2/exiv2.hpp>
#include <QDebug>

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

Worker::~Worker()
{
}

void Worker::process()
{
    try {
        Exiv2::ImageFactory::open("C:\\Path_to\\invalid_file.tiff");
    } catch (...) {
        qDebug() << "meow";
    }
    emit finished();
}

in mainwindow.cpp

void MainWindow::on_pushButton_clicked()
{
    ui->pushButton->setEnabled(false); // ignore this
    auto t = new QThread;
    auto w = new Worker;
    w->moveToThread(t);
    connect(t, &QThread::started, w, &Worker::process);
    connect(w, &Worker::finished, t, &QThread::quit);
    connect(w, &Worker::finished, w, &Worker::deleteLater);
    connect(t, &QThread::finished, t, &QThread::deleteLater);
    connect(t, &QThread::finished, this, &MainWindow::enableButton);
    t->start();
}

So far, works as expected. Do you do anything else with Exiv besides that in your code / in another thread? Maybe some part of the exiv library isn't thread-safe.

[qmmj]

Hi Wieland,

I've just tested your code on Windows/MSVC2015 and it crashed. I've also tested my code on Linux and there it works.

From the beginning I would have been glad to develop under Linux, but I rely on some Windows hardware driver.

One Question regarding your code: You included unistd.h . Is this for purpose or some leftover?

Have you some more idea what could be the reason?