SIGSEGV after adding QFileDialog::getOpenFileName to the program

cdwijs

@jsulm said in SIGSEGV after adding QFileDialog::getOpenFileName to the program:

@cdwijs I doubt this line is the reason for the crash especially if it happens several minutes later. You should run your app through debugger. Also what else are you doing in your app?
Also: is the file open dialog open when your app crashes or already closed?

I am running the app via the debugger, I have looked at the callstacks of the different threads, but I could not figure out what caused the crash. Does the backtrace provide the same information, or can I copy-and-paste something from the debugger screens thats not in the backtrace?
I am doing nothing else in my app. It's one form with one button, and one clicked() handler.
The file open dialog is closed when the crash happens.
The crash does not happen when I comment the line.

I will reboot my machine, remove the build folder, and see if that solves the problem.

Cheers,
Cedric

m.sue

@cdwijs

Hi,

probably the this pointer is no longer valid when the file dialog goes out of scope. Maybe just try it with a nullptr.

-Michael.

jsulm

@m.sue Why should it not be valid? QFileDialog::getOpenFileName is static and blocking - the execution will continue when the dialog is closed. In the mean time MainWindow cannot be destroyed.

m.sue

I understood that the crash happens after closing the file dialog. I thought maybe even after closing the whole program. Closing the dialog does not mean that the .NET objects behind the scene are freed immediately.
I had had similar problems on WINDOWS 7 Enterprise but only in the debug version.
-Michael

cdwijs

I have rebooted my machine, and removed the build folder, and the .user file.
I have tried both of the following lines, they both crash, after about 2 minutes after the load file dialog is closed:

fileName = QFileDialog::getOpenFileName(this,tr("Open File"),"","Dxf Files(*.dxf);;All files(*.*)");
fileName = QFileDialog::getOpenFileName(Q_NULLPTR,tr("Open File"),"","Dxf Files(*.dxf);;All files(*.*)");

The crash also happens when the dialog is cancelled.
The crash does not happen when the file open dialog is opened, and kept open.
The crash does happen when the dialog is opened, cancelled, and then kept open again.

What can I do to make this work?
Cheers, Cedric

[Added code tags ~kshegunov]

jsulm

@cdwijs What else is your app doing?
@m-sue We are in the native C++ universe here not .Net :-)

cdwijs

@jsulm said in SIGSEGV after adding QFileDialog::getOpenFileName to the program:

@cdwijs What else is your app doing?
@m-sue We are in the native C++ universe here not .Net :-)

@jsulm: I have created the smallest program that shows the problem. Just run it, press the button, and cancel the file dialog. Then after 3 minutes the program crashes. Here is the complete source code:

#-------------------------------------------------
#
# Project created by QtCreator 2017-06-09T14:42:39
#
#-------------------------------------------------

QT       += core gui

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

TARGET = untitled2
TEMPLATE = app


SOURCES += main.cpp\
        mainwindow.cpp

HEADERS  += mainwindow.h

FORMS    += mainwindow.ui

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

private slots:
    void on_pushButton_clicked();

private:
    Ui::MainWindow *ui;
};

#endif // MAINWINDOW_H

#include "mainwindow.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();

    return a.exec();
}

#include "mainwindow.h"
#include "ui_mainwindow.h"

#include <QFileDialog>

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

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

void MainWindow::on_pushButton_clicked()
{
    QString fileName;
    fileName = QFileDialog::getOpenFileName(Q_NULLPTR,tr("Open File"),"","Dxf Files(*.dxf);;All files(*.*)");
}

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>MainWindow</class>
 <widget class="QMainWindow" name="MainWindow">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>400</width>
    <height>300</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>MainWindow</string>
  </property>
  <widget class="QWidget" name="centralWidget">
   <widget class="QPushButton" name="pushButton">
    <property name="geometry">
     <rect>
      <x>40</x>
      <y>40</y>
      <width>75</width>
      <height>23</height>
     </rect>
    </property>
    <property name="text">
     <string>PushButton</string>
    </property>
   </widget>
  </widget>
  <widget class="QMenuBar" name="menuBar">
   <property name="geometry">
    <rect>
     <x>0</x>
     <y>0</y>
     <width>400</width>
     <height>21</height>
    </rect>
   </property>
  </widget>
  <widget class="QToolBar" name="mainToolBar">
   <attribute name="toolBarArea">
    <enum>TopToolBarArea</enum>
   </attribute>
   <attribute name="toolBarBreak">
    <bool>false</bool>
   </attribute>
  </widget>
  <widget class="QStatusBar" name="statusBar"/>
 </widget>
 <layoutdefault spacing="6" margin="11"/>
 <resources/>
 <connections/>
</ui>

14:44:14: Running steps for project untitled2...
14:44:14: Starting: "C:\Qt\5.8\mingw53_32\bin\qmake.exe" C:\Users\crldewijs\Documents\untitled2\untitled2.pro -spec win32-g++ "CONFIG+=debug" "CONFIG+=qml_debug"
Info: creating stash file C:\Users\crldewijs\Documents\build-untitled2-Desktop-Debug\.qmake.stash
14:44:15: The process "C:\Qt\5.8\mingw53_32\bin\qmake.exe" exited normally.
14:44:15: Starting: "C:\Qt\Tools\mingw530_32\bin\mingw32-make.exe" qmake_all
mingw32-make: Nothing to be done for 'qmake_all'.
14:44:15: The process "C:\Qt\Tools\mingw530_32\bin\mingw32-make.exe" exited normally.
14:44:15: Starting: "C:\Qt\Tools\mingw530_32\bin\mingw32-make.exe" 
C:/Qt/Tools/mingw530_32/bin/mingw32-make -f Makefile.Debug
mingw32-make[1]: Entering directory 'C:/Users/crldewijs/Documents/build-untitled2-Desktop-Debug'
C:\Qt\5.8\mingw53_32\bin\uic.exe ..\untitled2\mainwindow.ui -o ui_mainwindow.h
g++ -c -pipe -fno-keep-inline-dllexport -g -std=gnu++11 -frtti -Wall -Wextra -fexceptions -mthreads -DUNICODE -DQT_QML_DEBUG -DQT_WIDGETS_LIB -DQT_GUI_LIB -DQT_CORE_LIB -DQT_NEEDS_QMAIN -I..\untitled2 -I. -I..\..\..\..\Qt\5.8\mingw53_32\include -I..\..\..\..\Qt\5.8\mingw53_32\include\QtWidgets -I..\..\..\..\Qt\5.8\mingw53_32\include\QtGui -I..\..\..\..\Qt\5.8\mingw53_32\include\QtANGLE -I..\..\..\..\Qt\5.8\mingw53_32\include\QtCore -Idebug -I. -I..\..\..\..\Qt\5.8\mingw53_32\mkspecs\win32-g++  -o debug\main.o ..\untitled2\main.cpp
g++ -c -pipe -fno-keep-inline-dllexport -g -std=gnu++11 -frtti -Wall -Wextra -fexceptions -mthreads -DUNICODE -DQT_QML_DEBUG -DQT_WIDGETS_LIB -DQT_GUI_LIB -DQT_CORE_LIB -DQT_NEEDS_QMAIN -I..\untitled2 -I. -I..\..\..\..\Qt\5.8\mingw53_32\include -I..\..\..\..\Qt\5.8\mingw53_32\include\QtWidgets -I..\..\..\..\Qt\5.8\mingw53_32\include\QtGui -I..\..\..\..\Qt\5.8\mingw53_32\include\QtANGLE -I..\..\..\..\Qt\5.8\mingw53_32\include\QtCore -Idebug -I. -I..\..\..\..\Qt\5.8\mingw53_32\mkspecs\win32-g++  -o debug\mainwindow.o ..\untitled2\mainwindow.cpp
g++ -pipe -fno-keep-inline-dllexport -g -std=gnu++11 -frtti -Wall -Wextra -dM -E -o debug\moc_predefs.h ..\..\..\..\Qt\5.8\mingw53_32\mkspecs\features\data\dummy.cpp
C:\Qt\5.8\mingw53_32\bin\moc.exe -DUNICODE -DQT_QML_DEBUG -DQT_WIDGETS_LIB -DQT_GUI_LIB -DQT_CORE_LIB -DQT_NEEDS_QMAIN --include debug/moc_predefs.h -IC:/Qt/5.8/mingw53_32/mkspecs/win32-g++ -IC:/Users/crldewijs/Documents/untitled2 -IC:/Qt/5.8/mingw53_32/include -IC:/Qt/5.8/mingw53_32/include/QtWidgets -IC:/Qt/5.8/mingw53_32/include/QtGui -IC:/Qt/5.8/mingw53_32/include/QtANGLE -IC:/Qt/5.8/mingw53_32/include/QtCore -I. -IC:/Qt/Tools/mingw530_32/lib/gcc/i686-w64-mingw32/5.3.0/include -IC:/Qt/Tools/mingw530_32/lib/gcc/i686-w64-mingw32/5.3.0/include-fixed -IC:/Qt/Tools/mingw530_32/i686-w64-mingw32/include -IC:/Qt/Tools/mingw530_32/i686-w64-mingw32/include/c++ -IC:/Qt/Tools/mingw530_32/i686-w64-mingw32/include/c++/i686-w64-mingw32 -IC:/Qt/Tools/mingw530_32/i686-w64-mingw32/include/c++/backward ..\untitled2\mainwindow.h -o debug\moc_mainwindow.cpp
g++ -c -pipe -fno-keep-inline-dllexport -g -std=gnu++11 -frtti -Wall -Wextra -fexceptions -mthreads -DUNICODE -DQT_QML_DEBUG -DQT_WIDGETS_LIB -DQT_GUI_LIB -DQT_CORE_LIB -DQT_NEEDS_QMAIN -I..\untitled2 -I. -I..\..\..\..\Qt\5.8\mingw53_32\include -I..\..\..\..\Qt\5.8\mingw53_32\include\QtWidgets -I..\..\..\..\Qt\5.8\mingw53_32\include\QtGui -I..\..\..\..\Qt\5.8\mingw53_32\include\QtANGLE -I..\..\..\..\Qt\5.8\mingw53_32\include\QtCore -Idebug -I. -I..\..\..\..\Qt\5.8\mingw53_32\mkspecs\win32-g++  -o debug\moc_mainwindow.o debug\moc_mainwindow.cpp
g++ -Wl,-subsystem,windows -mthreads -o debug\untitled2.exe debug/main.o debug/mainwindow.o debug/moc_mainwindow.o  -lmingw32 -LC:\Qt\5.8\mingw53_32\lib C:\Qt\5.8\mingw53_32\lib\libqtmaind.a -LC:\utils\my_sql\my_sql\lib -LC:\utils\postgresql\pgsql\lib -lshell32 C:\Qt\5.8\mingw53_32\lib\libQt5Widgetsd.a C:\Qt\5.8\mingw53_32\lib\libQt5Guid.a C:\Qt\5.8\mingw53_32\lib\libQt5Cored.a 
mingw32-make[1]: Leaving directory 'C:/Users/crldewijs/Documents/build-untitled2-Desktop-Debug'
14:44:21: The process "C:\Qt\Tools\mingw530_32\bin\mingw32-make.exe" exited normally.
14:44:21: Elapsed time: 00:07.

m.sue

@cdwijs

In the backtrace #9 there is a call to IUnknown_QueryService which I assume causes the error, as in #8 in the networkitemfactory dll does not know what to do about it, initiating error handling in ole32.dll.

This maybe something completely independent of your program, like dll injection via explorer, virus scanner etc.

-Michael.

kshegunov

@jsulm said in SIGSEGV after adding QFileDialog::getOpenFileName to the program:

In the mean time MainWindow cannot be destroyed.

Actually it can. The blocking QEventLoop::exec is "fake" blocking, it still spins the global event loop, and as consequence Window's message loop.

@cdwijs
Try it without using the static overloads to exclude any funny business with the event loop:

QFileDialog * dialog = new QFileDialog(this, ...);
// ... setFileNameFilters and such
dialog->show();

QObject::connect(dialog, &QDialog::rejected, this, [] () {
    qDebug() << "Canceled ...";
});
QObject::connect(dialog, &QDialog::accepted, this, [] () {
    qDebug() << "Ok clicked ...";
});

If your problem persists, try setting the dialog to be alien (non-native) and get back with the results of your experiments. Also disable any antivirus stuff which may interfere as @m-sue suggested.

cdwijs

@kshegunov said in SIGSEGV after adding QFileDialog::getOpenFileName to the program:

@jsulm said in SIGSEGV after adding QFileDialog::getOpenFileName to the program:

In the mean time MainWindow cannot be destroyed.

Actually it can. The blocking QEventLoop::exec is "fake" blocking, it still spins the global event loop, and as consequence Window's message loop.

@cdwijs
Try it without using the static overloads to exclude any funny business with the event loop:
QFileDialog * dialog = new QFileDialog(this, ...);
// ... setFileNameFilters and such
dialog->show();

QObject::connect(dialog, &QDialog::rejected, this, [] () {
    qDebug() << "Canceled ...";
});
QObject::connect(dialog, &QDialog::accepted, this, [] () {
    qDebug() << "Ok clicked ...";
});
If your problem persists, try setting the dialog to be alien (non-native) and get back with the results of your experiments. Also disable any antivirus stuff which may interfere as @m-sue suggested.

I have tried some things, using non-native dialog works. It looks like every native dialog fails. See the below code:

#include "mainwindow.h"
#include "ui_mainwindow.h"

#include <QFileDialog>
QFileDialog * dialog;
#include <QDebug>


MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    dialog = new QFileDialog();
    QObject::connect(dialog,&QFileDialog::fileSelected,this, [] () {qDebug()<<"fileselected";}); //fires on pushbutton 2 dialog
    ui->setupUi(this);
}

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

void MainWindow::on_pushButton_clicked()
{
    QString fileName;
    fileName = QFileDialog::getOpenFileName(Q_NULLPTR,tr("Open File"),"","Dxf Files(*.dxf);;All files(*.*)"); //sigseg after 2 minutes
}

void MainWindow::on_pushButton_2_clicked()
{
    dialog->show(); //no crash (tested 9 minutes), looks non-native
}



void MainWindow::on_pushButton_3_clicked()
{
    QString fileName;
    fileName = dialog->getOpenFileName(Q_NULLPTR,tr("Open File"),"","Dxf Files(*.dxf);;All files(*.*)"); //sigseg after 2 minutes
}

void MainWindow::on_pushButton_4_clicked()
{
    QString fileName;
    fileName = dialog->getOpenFileName(); //sigseg after 2 minutes
}



void MainWindow::on_pushButton_5_clicked()
{
    QString fileName;
    fileName = QFileDialog::getOpenFileName(Q_NULLPTR,tr("Open File"),"","Dxf Files(*.dxf);;All files(*.*)",Q_NULLPTR,QFileDialog::DontUseNativeDialog); //no crash, looks non-native
}

Rondog

I don't know if this is helpful or not but I ran into a problem a few years back that reminds me of this. A (non-Qt) software I dealt with would crash every time the the user would access the file dialogs (open, save) and it seemed to happen only to certain people. If files were loaded from the recent file list everything was fine. Everything worked until you tried to do something with the file dialogs.

The problem turned out to be a name collision of a DLL and Office 2013. With Office 2013 installed everytime the open or save dialog was called and there was a DLL present with a name it thought was somehow assocated with Office 2013 the result was a crash. The solution this (rather large) software company came up with was to rename their DLL file (lol).

First I am assuming your program would work on a clean install of Windows 7 with nothing else installed. I have never had this kind of problem using the Qt file dialogs (not like this at least) so I suspect this would be true. I have not used Qt 5.8.x but 5.6.x does not have this problem on Win7.

joeQ

@cdwijs Hi, friend, welcome.

did you try add QFileDialog::DontUseNativeDialog ?

i got crash problem in my windows system before . I used the Qt Don't Native Dialog, It worked out. I guess it was the Permission issues. sometime, use the native dialog, it will crashed. but sometimes, it also can worked well.


#ifdef USE_NATIVE_DIALOG
    path = QFileDialog::getOpenFileName(this,tr("select file"), lastDir,FILE_FILTER, 0,QFileDialog::DontUseNativeDialog );
#else
    path = QFileDialog::getOpenFileName(this,tr("select file"), lastDir, FILE_FILTER);
#endif