Qt Application Crash

[Mr .Wu]

I have make a application in Qt . It running on Qt 5.8 platform . I use a mousearea control . I found that When I double click quickly . The Application will be crash .

the crash log :

Program received signal SIGSEGV, Segmentation fault.
0xb6da7b0c in QQuickEventPoint::grabber() const ()
from /data/qt/lib/libQt5Quick.so.5
(gdb) bt
bt
#0 0xb6da7b0c in QQuickEventPoint::grabber() const ()
from /data/qt/lib/libQt5Quick.so.5
#1 0xb6e3d100 in QQuickMouseArea::mouseReleaseEvent(QMouseEvent*) ()
from /data/qt/lib/libQt5Quick.so.5
#2 0xb6dc2678 in QQuickItem::event(QEvent*) ()
from /data/qt/lib/libQt5Quick.so.5
#3 0xb60c3278 in QCoreApplicationPrivate::notify_helper(QObject*, QEvent*) ()
from /data/qt/lib/libQt5Core.so.5
#4 0xb60c3408 in QCoreApplication::notify(QObject*, QEvent*) ()
from /data/qt/lib/libQt5Core.so.5
#5 0xb60c3338 in QCoreApplication::notifyInternal2(QObject*, QEvent*) ()
from /data/qt/lib/libQt5Core.so.5
#6 0xb6dd411c in QQuickWindowPrivate::deliverTouchAsMouse(QQuickItem*, QQuickPo
interEvent*) () from /data/qt/lib/libQt5Quick.so.5
#7 0xb6dd4c54 in QQuickWindowPrivate:: (QQuickItem*,
QQuickPointerEvent*, QSet<QQuickItem*>) () from /data/qt/lib/libQt5Quick.so.5
#8 0xb6dd4ec8 in QQuickWindowPrivate::deliverUpdatedTouchPoints(QQuickPointerTo
uchEvent, QSet<QQuickItem*>) () from /data/qt/lib/libQt5Quick.so.5
#9 0xb6dd5af8 in QQuickWindowPrivate::deliverTouchEvent(QQuickPointerTouchEvent
) () from /data/qt/lib/libQt5Quick.so.5
#10 0xb6dd5bdc in QQuickWindowPrivate::deliverPointerEvent(QQuickPointerEvent)
() from /data/qt/lib/libQt5Quick.so.5
#11 0xb6dd65b8 in QQuickWindowPrivate::handleTouchEvent(QTouchEvent) ()
---Type <return> to continue, or q <return> to quit---

from /data/qt/lib/libQt5Quick.so.5
#12 0xb6dd7e3c in QQuickWindow::event(QEvent*) ()
from /data/qt/lib/libQt5Quick.so.5
#13 0xb60c3278 in QCoreApplicationPrivate::notify_helper(QObject*, QEvent*) ()
from /data/qt/lib/libQt5Core.so.5
#14 0xb60c3408 in QCoreApplication::notify(QObject*, QEvent*) ()
from /data/qt/lib/libQt5Core.so.5
#15 0xb60c3338 in QCoreApplication::notifyInternal2(QObject*, QEvent*) ()
from /data/qt/lib/libQt5Core.so.5
#16 0xb68ec1a8 in QGuiApplicationPrivate::processTouchEvent(QWindowSystemInterfa
cePrivate::TouchEvent*) () from /data/qt/lib/libQt5Gui.so.5
#17 0xb68eef38 in QGuiApplicationPrivate::processWindowSystemEvent(QWindowSystem
InterfacePrivate::WindowSystemEvent*) () from /data/qt/lib/libQt5Gui.so.5
#18 0xb68c89f8 in QWindowSystemInterface::sendWindowSystemEvents(QFlags<QEventLo
op::ProcessEventsFlag>) () from /data/qt/lib/libQt5Gui.so.5
#19 0xb5cb8600 in QUnixEventDispatcherQPA::processEvents(QFlags<QEventLoop::Proc
essEventsFlag>) () from /data/qt/plugins/platforms/libqlinuxfb.so
#20 0xb60c0f18 in QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag

) () from /data/qt/lib/libQt5Core.so.5
#21 0xb60c1328 in QEventLoop::exec(QFlagsQEventLoop::ProcessEventsFlag) ()
from /data/qt/lib/libQt5Core.so.5
#22 0xb60c9980 in QCoreApplication::exec() () from /data/qt/lib/libQt5Core.so.5
#23 0x00016a84 in main (argc=0, argv=<optimized out>) at main.cpp:155
(gdb)

(gdb)

(gdb) bt

[ambershark]

@Mr-.Wu Can you share the QML code (or better yet a minimal example) that can duplicate the crash?

[Mr .Wu]

Chat.qml

import QtQuick 2.4
import "qrc:/ui/javascript/watch_constants.js" as Constants
import "qrc:/ui/javascript/watch_functions.js" as Functions

ChatForm {
    id: chatForm

    Connections {
        target: btnChat
        onClicked: {
            Functions.getWindow("ChatWindow.qml").createChatListComponent()
        }
    }
}

ChatForm.ui.qml

import QtQuick 2.7
import QtQuick.Controls 2.0
import QtQuick.Layouts 1.0
import "qrc:/ui/javascript/watch_constants.js" as Constants

Item {
    width: 240
    height: 240

    property alias txtChat: txtChat
    property alias btnChat: btnChat

    Rectangle {
        id: rectangleChatsArea
        anchors.fill : parent
        color: Constants.LauncherBgColor

        Image {
            id: imageChatBg
            source: "qrc:/ui/images/launcher_bg.png"
            width: parent.width
            height: parent.height
        }

        Rectangle {
            height: 115
            width: 115
            anchors.verticalCenter: parent.verticalCenter
            anchors.horizontalCenter: parent.horizontalCenter
            color: Constants.LauncherColor_Transparent

            Image {
                id: imageChatIoc
                source: "qrc:/ui/images/chat_ioc.png"
            }
            MouseArea {
                id: btnChat
                anchors.fill: parent
            }
        }
        Text {
            id: txtChat
            font.pixelSize: Constants.LauncherFontPixelSize
            font.family: Constants.LauncherFontFamily
            horizontalAlignment: Text.AlignHCenter
            anchors.bottom: parent.bottom
            anchors.bottomMargin: 24
            anchors.horizontalCenter: parent.horizontalCenter
            color: Constants.LauncherTextColor
            width: 72
            height: 24
        }
    }
}

RootWindow.qml

import QtQuick 2.7
import QtQuick.Window 2.2
import "qrc:/ui/javascript/watch_constants.js" as Constants
import "qrc:/ui/javascript/watch_functions.js" as Functions

Window {
    id: rootWindow
    x: 0
    y: 0
    width: 240
    height: 240
    flags: Qt.FramelessWindowHint

    // 显示区域
    property alias rootRectangle: rootRectangle
    // 窗体组件(当前显示的组件)
    property var component: null
    // 点击事件
    property alias rootMouseArea: rootMouseArea


    Rectangle {
        x: 0
        y: 0
        id: rootRectangle
        width: parent.width
        height: parent.height
        color: Constants.LauncherBgColor

        MouseArea {
            x: 0
            y: 0
            id: rootMouseArea
            anchors.fill: parent
        }
    }

    /************************************************** Function *******************************************************/

    // 创建组件
    function setupComponent(qml_file) {
        return setupComponentVisible(qml_file, true)
    }


    // 创建组件
    function setupComponentVisible(qml_file, visible) {
        var parent = null
        if (component == null)
            parent = rootRectangle
        else
            parent = component
        var ret = Functions.dynamicCreateComponent(parent, qml_file, visible)
        if (ret != null)
            component = ret
        if(visible)
            component.visible = true
        return component
    }
}

watch_functions.js

/*
 * Func: create component
 * Desc: dynamic create component
 * Para: parent , qml file , visible - true or false
 * Ret : component
 */
function dynamicCreateComponent(parent,qml_file,visible)
{
    if(parent == null)
    {
        console.log("create component failed . the parent is null .");
        return null;
    }
    if(qml_file == null)
    {
        console.log("create component failed . the qml file is null .");
        return null;
    }

    var component = Qt.createComponent(qml_file);
    var qml_object = component.createObject(parent,{"x": 0, "y": 0});
    if(qml_object !=null)
        qml_object.visible = visible;

    console.log("create component : " + qml_object + " , parent : " + qml_object.parent);
    return qml_object;
}

/*
 * Func: get window
 * Desc: get window
 * Para: window name
 * Ret :
 */
function getWindow(window_name)
{
    if(window_name == null)
    {
        console.log("the window name is null . can't get it .");
        return null;
    }
    var window = ui_management.existsWindow(window_name);
    if(window == null)
    {
        console.log("can't find the window named : " + window_name);
        return null;
    }
    return window.getQmlObject();
}

ChatWindow.qml

import QtQuick 2.7
import QtQuick.Controls 2.0
import QtQuick.Layouts 1.0
import "qrc:/ui"
import "qrc:/ui/javascript/watch_constants.js" as Constants
import "qrc:/ui/javascript/watch_functions.js" as Functions

RootWindow {
    id: chatWindow
    visible: false
    width: 240
    height: 240

    signal
    createChatListComponent;

    Component.onCompleted: {
        createChatListComponent.connect(setupListView)
        console.log("Chat Window Completed")
    }

    Component.onDestruction: {
        createChatListComponent.disconnect(setupListView)
        console.log("Chat Window Destruction")
    }

    /************************************************** Function *******************************************************/

    // 打开消息列表
    function setupListView() {
        setupComponent(Constants.Compontent_ChatList)
    }
}

[Mr .Wu]

When I double click quickly the mousearea named btnChat . The Application will be crash . This is a probabilistic event

[Mr .Wu]

@ambershark can you found the problem ?

[ambershark]

@Mr-.Wu I'll play with it tomorrow and see if it crashes for me. I'll let you know.

Edit: Sorry didn't have time today, but will try to check it this week for sure. Busy time deadline wise for me right now.

[Mr .Wu]

@ambershark said in Qt Application Crash:

Sorry didn't have time today, but will try to check it this week for sure. Busy time deadline wise for me right now.

Okay. Thanks

[Mr .Wu]

@ambershark Did you do the test?

[ambershark]

@Mr-.Wu Sorry I haven't yet. I have a tight deadline and had to write a ton of code this week. Worked some 12 hour days. I will try to test it soon though. Hopefully someone else can give it a shot too so you're not waiting on just me.

[Mr .Wu]

@ambershark Can you help us . We can't found the problem how to cause.

[Schluchti]

@Mr-.Wu Have you tried running the code with Qt 5.9? 5.9 is a long term release and if it's really a bug chances are good that it will be fixed with one of the bugfix releases.

[ambershark]

@Mr-.Wu Ok finally had some time today to look at it. With the code you provided I can't get it to run as it's missing things.

So here's what we can do. Can you provide a simple example that duplicates the behavior? Does this happen with any mousearea or is it specific to one in your project? If you setup just a simple rect with a mousearea could you get it to crash? Does it crash while running in qmlscene or only when you run as an app?:

I tested with the following code:

import QtQuick 2.4
import QtQuick.Controls 2.0

Rectangle {
        width: 400
        height: 400
        color: "black"

        MouseArea {
                anchors.fill: parent
                onClicked: { parent.color = "red" }
                onDoubleClicked: { parent.color = "black" }
        }
}

Everything was fine as fast as I could click. I just ran it with qmlscene though. Try that on your system and see if you can duplicate the crash if not, see what is different between how you use a MouseArea and what this simple one is doing. Then try to step it from a base MouseArea to your and find the point at which it breaks.

If you could give me a working project I could test yours and see if I can find the issue. I'm still learning QML myself though. I've been using Qt with QtWidgets for a very long time but am pretty new to QML as of last year. And since I haven't had a big project that needed it I just haven't had the exposure to the small problems it can produce yet. So I don't see anything obvious in your code.