Program crashed after close the mainwindow

[toming]

Environment:
macOS 10.15.4
Qt: 5.12.8
Qt Creator: 4.11.2 (based on Qt 5.14.2 Clang 10.0.0)

I got this output after I quit the program (Command + Q)

02:47:10: The process was ended forcefully.
02:47:10: xxx/build-surimage-tool-Desktop_Qt_5_12_8_clang_64bit-Debug/surimage-tool.app/Contents/MacOS/surimage-tool crashed.

Here is my main.cpp

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

I find this line has to do with the crash:

/* mainwindow.cpp */
MainWindow::~MainWindow() {
    // the line causing the crash
    // the crash disappears as soon as I comment the following line
    delete ui; 
}

where ui is defined as

/* mainwindow.h */
private:
    Ui::MainWindow *ui;

and here is my ui header (automatically generated by ui designer)

/********************************************************************************
** Form generated from reading UI file 'mainwindow.ui'
**
** Created by: Qt User Interface Compiler version 5.12.8
**
** WARNING! All changes made in this file will be lost when recompiling UI file!
********************************************************************************/

#ifndef UI_MAINWINDOW_H
#define UI_MAINWINDOW_H

#include <QtCore/QVariant>
#include <QtWidgets/QAction>
#include <QtWidgets/QApplication>
#include <QtWidgets/QGridLayout>
#include <QtWidgets/QLabel>
#include <QtWidgets/QMainWindow>
#include <QtWidgets/QMenu>
#include <QtWidgets/QMenuBar>
#include <QtWidgets/QStatusBar>
#include <QtWidgets/QToolBar>
#include <QtWidgets/QWidget>

QT_BEGIN_NAMESPACE

class Ui_MainWindow
{
public:
    QAction *actionCapture;
    QAction *actionRecord;
    QAction *action_4;
    QAction *action_5;
    QAction *actionCalibrate;
    QAction *actionStartCamera;
    QAction *actionStopCamera;
    QWidget *centralwidget;
    QGridLayout *gridLayout;
    QGridLayout *gridLayout_2;
    QLabel *labelDisplay_1;
    QLabel *labelDisplay_2;
    QLabel *labelDisplay_3;
    QMenuBar *menubar;
    QMenu *menuFile;
    QMenu *menuDevices;
    QStatusBar *statusbar;
    QToolBar *toolBar;

    void setupUi(QMainWindow *MainWindow)
    {
        if (MainWindow->objectName().isEmpty())
            MainWindow->setObjectName(QString::fromUtf8("MainWindow"));
        MainWindow->resize(800, 600);
        actionCapture = new QAction(MainWindow);
        actionCapture->setObjectName(QString::fromUtf8("actionCapture"));
        actionRecord = new QAction(MainWindow);
        actionRecord->setObjectName(QString::fromUtf8("actionRecord"));
        action_4 = new QAction(MainWindow);
        action_4->setObjectName(QString::fromUtf8("action_4"));
        action_5 = new QAction(MainWindow);
        action_5->setObjectName(QString::fromUtf8("action_5"));
        actionCalibrate = new QAction(MainWindow);
        actionCalibrate->setObjectName(QString::fromUtf8("actionCalibrate"));
        actionStartCamera = new QAction(MainWindow);
        actionStartCamera->setObjectName(QString::fromUtf8("actionStartCamera"));
        actionStopCamera = new QAction(MainWindow);
        actionStopCamera->setObjectName(QString::fromUtf8("actionStopCamera"));
        centralwidget = new QWidget(MainWindow);
        centralwidget->setObjectName(QString::fromUtf8("centralwidget"));
        gridLayout = new QGridLayout(centralwidget);
        gridLayout->setObjectName(QString::fromUtf8("gridLayout"));
        gridLayout_2 = new QGridLayout();
        gridLayout_2->setObjectName(QString::fromUtf8("gridLayout_2"));
        labelDisplay_1 = new QLabel(centralwidget);
        labelDisplay_1->setObjectName(QString::fromUtf8("labelDisplay_1"));
        QSizePolicy sizePolicy(QSizePolicy::Preferred, QSizePolicy::Preferred);
        sizePolicy.setHorizontalStretch(0);
        sizePolicy.setVerticalStretch(0);
        sizePolicy.setHeightForWidth(labelDisplay_1->sizePolicy().hasHeightForWidth());
        labelDisplay_1->setSizePolicy(sizePolicy);

        gridLayout_2->addWidget(labelDisplay_1, 0, 0, 1, 1);

        labelDisplay_2 = new QLabel(centralwidget);
        labelDisplay_2->setObjectName(QString::fromUtf8("labelDisplay_2"));
        sizePolicy.setHeightForWidth(labelDisplay_2->sizePolicy().hasHeightForWidth());
        labelDisplay_2->setSizePolicy(sizePolicy);

        gridLayout_2->addWidget(labelDisplay_2, 0, 1, 1, 1);

        labelDisplay_3 = new QLabel(centralwidget);
        labelDisplay_3->setObjectName(QString::fromUtf8("labelDisplay_3"));

        gridLayout_2->addWidget(labelDisplay_3, 1, 0, 1, 1);


        gridLayout->addLayout(gridLayout_2, 0, 0, 1, 1);

        MainWindow->setCentralWidget(centralwidget);
        menubar = new QMenuBar(MainWindow);
        menubar->setObjectName(QString::fromUtf8("menubar"));
        menubar->setGeometry(QRect(0, 0, 800, 22));
        menuFile = new QMenu(menubar);
        menuFile->setObjectName(QString::fromUtf8("menuFile"));
        menuDevices = new QMenu(menubar);
        menuDevices->setObjectName(QString::fromUtf8("menuDevices"));
        MainWindow->setMenuBar(menubar);
        statusbar = new QStatusBar(MainWindow);
        statusbar->setObjectName(QString::fromUtf8("statusbar"));
        MainWindow->setStatusBar(statusbar);
        toolBar = new QToolBar(MainWindow);
        toolBar->setObjectName(QString::fromUtf8("toolBar"));
        MainWindow->addToolBar(Qt::TopToolBarArea, toolBar);

        menubar->addAction(menuFile->menuAction());
        menubar->addAction(menuDevices->menuAction());
        menuFile->addAction(actionStartCamera);
        menuFile->addAction(actionStopCamera);
        menuFile->addAction(actionCapture);
        menuFile->addAction(actionRecord);
        menuFile->addSeparator();
        menuFile->addAction(action_4);
        menuFile->addAction(action_5);
        menuFile->addSeparator();
        menuFile->addAction(actionCalibrate);
        menuFile->addSeparator();
        toolBar->addAction(actionCapture);
        toolBar->addAction(actionRecord);
        toolBar->addAction(actionCalibrate);

        retranslateUi(MainWindow);

        QMetaObject::connectSlotsByName(MainWindow);
    } // setupUi

    void retranslateUi(QMainWindow *MainWindow)
    {
        MainWindow->setWindowTitle(QApplication::translate("MainWindow", "Surimage Tool", nullptr));
        actionCapture->setText(QApplication::translate("MainWindow", "\346\213\215\347\205\247", nullptr));
        actionRecord->setText(QApplication::translate("MainWindow", "\345\275\225\345\203\217", nullptr));
        action_4->setText(QApplication::translate("MainWindow", "\345\210\266\344\275\234\345\233\272\344\273\266", nullptr));
        action_5->setText(QApplication::translate("MainWindow", "\346\233\264\346\226\260\345\233\272\344\273\266", nullptr));
        actionCalibrate->setText(QApplication::translate("MainWindow", "\346\240\207\345\256\232", nullptr));
        actionStartCamera->setText(QApplication::translate("MainWindow", "\345\220\257\345\212\250", nullptr));
        actionStopCamera->setText(QApplication::translate("MainWindow", "\345\201\234\346\255\242", nullptr));
        labelDisplay_1->setText(QApplication::translate("MainWindow", "TextLabel", nullptr));
        labelDisplay_2->setText(QApplication::translate("MainWindow", "TextLabel", nullptr));
        labelDisplay_3->setText(QApplication::translate("MainWindow", "TextLabel", nullptr));
        menuFile->setTitle(QApplication::translate("MainWindow", "\346\226\207\344\273\266", nullptr));
        menuDevices->setTitle(QApplication::translate("MainWindow", "\350\256\276\345\244\207", nullptr));
        toolBar->setWindowTitle(QApplication::translate("MainWindow", "toolBar", nullptr));
    } // retranslateUi

};

namespace Ui {
    class MainWindow: public Ui_MainWindow {};
} // namespace Ui

QT_END_NAMESPACE

#endif // UI_MAINWINDOW_H

Since MainWindow w is the parent of all the components of the ui, I think it's definitely okay leave the cleaning work to the MainWindow w since w itself is created on the stack. But according to Qt it is also fine to delete the ui manually, I'm very confused why delete ui would cause the program crash on exiting?

Surely I have code in some other files, but I don't think they are related to the problem.

In the Qt Example: Camera, I find that it doesn't delete ui, so when I add the delete ui for it's mainwindow, the crash occurs. Is it abnormal?

[SGaist]

Hi and welcome to devnet,

Can you show your MainWindow header as well as the constructor code ?

[toming]

@SGaist Yes (sorry I have to wait 10min before the forum allows me to post again)

/* mainwindow.h */
#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QCamera>
#include <QCameraImageCapture>
#include <QMediaRecorder>
#include <QScopedPointer>
#include <QCloseEvent>

#include "survideosurface.h"

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

private slots:
    void setCamera(const QCameraInfo&);
    void updateCameraState(QCamera::State);
    void updateCameraDevice(QAction*);
    void displayCameraError();
    void rcvFrame(QVideoFrame& m_currentFrame);
    // void updateCaptureMode();



private:
    Ui::MainWindow *ui;

    QScopedPointer<QCamera> m_camera;
    SurVideoSurface* m_video_surface;// camera==>video_surface
};
#endif // MAINWINDOW_H

and

/* mainwindow.cpp */
Q_DECLARE_METATYPE(QCameraInfo)

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

  // Camera devices:
  QActionGroup *videoDevicesGroup = new QActionGroup(this);
  videoDevicesGroup->setExclusive(true);
  const QList<QCameraInfo> availableCameras = QCameraInfo::availableCameras();
  for (const QCameraInfo &cameraInfo : availableCameras) {
    QAction *videoDeviceAction =
        new QAction(cameraInfo.description(), videoDevicesGroup);
    videoDeviceAction->setCheckable(true);
    qDebug() << cameraInfo.description();
    videoDeviceAction->setData(
        QVariant::fromValue(cameraInfo)); // TODO: confused
    if (cameraInfo == QCameraInfo::defaultCamera())
      videoDeviceAction->setChecked(true);

    ui->menuDevices->addAction(videoDeviceAction);
  }

  connect(videoDevicesGroup, &QActionGroup::triggered, this,
          &MainWindow::updateCameraDevice);
  //  connect(ui->captureWidget, &QTabWidget::currentChanged, this,
  //          &Camera::updateCaptureMode);

  setCamera(QCameraInfo::defaultCamera());
}

[SGaist]

Do you have the stack trace of the crash ?
I am suspecting a double delete.

[toming]

@SGaist Double delete seems likely to me, too.
Unfortunately I don't know how to look at the stack trace yet, I'll learn the debugger first and then report back.

[toming]

@SGaist Now I have another discover, because I'm using the QCamera, I add a line before deleting the ui, then the crash goes away:

MainWindow::~MainWindow() {
    m_camera->stop();  // this is the new line
    delete ui;
}

I cannot dig into the stack trace of the crash because in debug mode, there's an error getting the MacBook Facetime camera on (that is another problem which I'm exploring), so the crash never happens in debug mode:

CMIO_DAL_PlugIn.cpp:269:StreamCopyBufferQueue Error: 1852797029, got an error from the plug-in routine