Hallo,

if I create an path object (class Path : public QObject, public QGraphicsPathItem) in an other std::thread then his parent item (class Anchor : public QObject, public QGraphicsPixmapItem), it crashes.
The funny thing is, that it doesn't crashes if the QMainWindow that holds the QGraphicScene has no parent. If it's parent is a QTabWidget it crashes.


Anchor.cpp
Qt Code: 
  1. void Anchor::addDistanceValue(double distanceValue) {
  2.     mutex.lock();
  3.     bool stillWorking = isWorking;
  4.     mutex.unlock();
  5.     if(!stillWorking){
  6.         mutex.lock();
  7.         isWorking = true;
  8.         mutex.unlock();
  9.         if (wallCheckerThread.joinable()){
  10.             //QTime timeStamp = QTime::currentTime();
  11.             wallCheckerThread.join();
  12.             //qDebug() << "wait to join anker: " << id << "in " << timeStamp.msecsTo(QTime::currentTime()) << "ms";
  13.         }
  14.  
  15.  
  16.  
  17.         wallCheckerThread = std::thread([&](double distanceValue){
  18.  
  19.             QTime timeStamp = QTime::currentTime();
  20.  
  21.             classMutex.lock();
  22.             mutex.lock();
  23.             Path* item = new Path(distanceValue * 100, this); // <<--- here is the problem, the this
  24.             mutex.unlock();
  25.             //item->setPos(pos());
  26.             item->setVisible(false);
  27.             //scene()->addItem(item);
  28.             classMutex.unlock();
  29.  
  30.  
  31.             checkAdditionalPathLossChanges(distanceValue, item);
  32.  
  33.             qDebug() << "Anker " << getId() << ": " << timeStamp.msecsTo(QTime::currentTime()) << "ms";
  34.  
  35.             QPen pen;
  36.             pen.setColor(0x8888ff);
  37.             item->setPen(pen);
  38.             item->setFlags(0);
  39.             item->setAcceptedMouseButtons(Qt::NoButton);
  40.  
  41.             distanceVector.push_back(distanceValue);
  42.  
  43.             ellipses.append(item);
  44.  
  45.             if (distanceVector.length() > 1){
  46.                 distanceVector.pop_front();
  47.  
  48.                 classMutex.lock();
  49.                 delete ellipses.first();
  50.                 //scene()->removeItem(ellipses.first());
  51.                 classMutex.unlock();
  52.  
  53.                 if (!ellipses.isEmpty())
  54.                     ellipses.pop_front();
  55.             }
  56.             item->setVisible(true);
  57.             mutex.lock();
  58.             isWorking = false;
  59.             mutex.unlock();
  60.         }, distanceValue);
  61.     }else{
  62.         qDebug() << "skipped anker " << id;
  63.     }
  64. }
To copy to clipboard, switch view to plain text mode 

path.h
Qt Code: 
  1. #include <QGraphicsItem>
  2. #include <QObject>
  3. #include <QGraphicsSceneMouseEvent>
  4.  
  5. class Path : public QObject, public QGraphicsPathItem
  6. {
  7.     Q_OBJECT
  8.     Q_INTERFACES(QGraphicsItem)
  9.  
  10. public:
  11.    explicit Path(qreal radius, QGraphicsItem *parent = 0):
  12.         QGraphicsPathItem(parent) // << here it crashes (path.h 15)
  13.     {
  14.         myPath = new QPainterPath();
  15.         myPath->addEllipse(QRectF(-radius,-radius,radius * 2, radius * 2));
  16.         setPath(*myPath);
  17.         setZValue(1);
  18.     }
  19.  
  20.     enum { Type = UserType + 3 };
  21.  
  22.     int type() const { return Type; }
  23.     void addPainterPath(QPainterPath path){ *myPath += path; setPath(*myPath);}
  24.     QPainterPath* getPainterPath() {return myPath; }
  25.  
  26. protected:
  27.    // QGraphicsEllipseItem *item;
  28.     void mousePressEvent(QGraphicsSceneMouseEvent *event){
  29.         QGraphicsPathItem::mousePressEvent(event);
  30.     }
  31.  
  32.     void mouseMoveEvent(QGraphicsSceneMouseEvent *event){
  33.         QGraphicsPathItem::mouseMoveEvent(event);
  34.     }
  35.     QPainterPath *myPath;
  36. };
To copy to clipboard, switch view to plain text mode 

working if its used this way:

Qt Code: 
  1. #include <QApplication>
  2. #include <QFile>
  3. #include <QObject>
  4. #include <QDebug>
  5. #include "serialwidget.h"
  6. #include "radarwidget.h"
  7.  
  8. int main(int argc, char *argv[])
  9. {
  10.     QApplication app(argc, argv);
  11.     RadarWidget radarWidget;
  12.     radarWidget.show();
  13.     SerialWidget mainWindow;
  14.     mainWindow.show();
  15.     QObject::connect(&mainWindow, SIGNAL(newDistanceData(int, double)), &radarWidget, SLOT(addNodeDistance(int, double)));
  16.     radarWidget.setSettingsProvider(mainWindow.getSettingsProvider());
  17.     return app.exec();
  18.  
  19.  
  20. ////////////////////////
  21.  
  22. just as additional info:
  23. the signal is passed to the right anchor
  24.  
  25.  
  26. void RadarGraphicsView::addNodeDistance(int id, double distance){
  27.     if(anchors.length() == 0){
  28.         QTimer *timer = new QTimer(this);
  29.         connect(timer, SIGNAL(timeout()), this, SLOT(calculateLocation()));
  30.         timer->start(1000);
  31.         QThread::msleep(20);
  32.     }
  33.  
  34.     for(int i = 0; i < anchors.length(); i++){
  35.         if(anchors.at(i)->getId() == id){
  36.             anchors.at(i)->addDistanceValue(distance);
  37.             anchors.at(i)->update();
  38.             this->scene()->update();
  39.             return;
  40.         }
  41.     }
  42.     Anchor::classMutex.lock();
  43.     Anchor *newAnchor = new Anchor(id);
  44.     this->scene()->addItem(newAnchor);
  45.     Anchor::classMutex.unlock();
  46.     double x = settings->getSetting(id, "x");
  47.     double y = settings->getSetting(id, "y");
  48.     newAnchor->setPos(x,y);
  49.     newAnchor->addDistanceValue(distance);
  50.     anchors.append(newAnchor);
  51. }
  52. ////////////////////////////////////////
  53. }
To copy to clipboard, switch view to plain text mode 


it isnt working this way:

Qt Code: 
  1. SerialWidget::SerialWidget(QWidget *parent) :
  2.     QMainWindow(parent),
  3.     ui(new Ui::SerialWidget)
  4. {
  5.     ui->setupUi(this);
  6.     Pi = 3.1415;
  7.     intValidator = new QIntValidator(0, 3000000, this);
  8.     ui->baudRateBox->setInsertPolicy(QComboBox::NoInsert);
  9.     connect(ui->serialPortInfoListBox, SIGNAL(currentIndexChanged(int)), this, SLOT(showPortInfo(int)));
  10.     connect(ui->baudRateBox, SIGNAL(currentIndexChanged(int)), this, SLOT(checkCustomBaudRatePolicy(int)));
  11.     //connect(ui->actionSaveMeasurement, SIGNAL(triggered())
  12.     //connect(ui->localEchoCheckBox, SIGNAL(clicked(bool)), ui->console, SLOT(setLocalEchoEnabled(bool)));
  13.     fillPortsParameters();
  14.     fillPortsInfo();
  15.     updateSettings();
  16.     this->showMaximized();
  17.     deviceData.clear();
  18.  
  19.     replayTool = new ReplayTool();
  20.     replayTool->moveToThread(&replayToolThread);
  21.     connect(replayTool, SIGNAL(sigDataRecieved(QByteArray)), this, SLOT(readData(QByteArray)));
  22.     replayToolThread.start(QThread::LowestPriority);
  23.  
  24.     ui->cBDeviceSelector->blockSignals(true);
  25.     ui->cBDeviceSelector->insertItem(0,"General Settings");
  26.     ui->cBDeviceSelector->blockSignals(false);
  27.     ui->cBDeviceSelector->setDuplicatesEnabled(false);
  28.     on_friisOkPushButton_clicked();
  29.     deviceSettings = new SettingsProvider(&friisDefaultSettings);
  30.  
  31.     rssiFilter = new RssiFilter();
  32.     isReplayPaused = false;
  33.     // if the qmainwindow is a chiild of this object ----------------------|
  34.     QObject::connect(this, SIGNAL(newDistanceData(int, double)), ui->sWRadar, SLOT(addNodeDistance(int, double))); // <<--- the radar is a child of the mainwindow
  35.     ui->sWRadar->setSettingsProvider(deviceSettings);
  36. }
To copy to clipboard, switch view to plain text mode 

the debugger says:

SIGSEGV
Segmantation fault


stack:
Qt Code: 
  1. 0	??			0x1d2bf51c	
  2. 1	QCoreApplicationPrivate::checkReceiverThread		513	0x6b929693	
  3. 2	QApplication::notify		2791	0x91eb4ba	
  4. 3	QCoreApplication::notifyInternal		935	0x6b929f96	
  5. 4	QCoreApplication::sendEvent		237	0x9536429	
  6. 5	QGraphicsScene::setFocus		2969	0x94a835a	
  7. 6	QGraphicsScenePrivate::setActivePanelHelper		743	0x94a1c63	
  8. 7	QGraphicsScene::setActivePanel		5644	0x94b180c	
  9. 8	QGraphicsItem::setActive		3188	0x94813fc	
  10. 9	QGraphicsItemPrivate::setParentItemHelper		1222	0x947b90a	
  11. 10	QGraphicsItem::setParentItem		1685	0x947ce1b	
  12. 11	QGraphicsItem::QGraphicsItem		1399	0x947c412	
  15. 14	Path::Path	path.h	15	0x43010a	
  16. 15	Anchor::__lambda2::operator()	anchor.cpp	364	0x40f3cb	
  17. 16	std::_Bind_simple<Anchor::addDistanceValue(double)::__lambda2(double)>::_M_invoke<0u>(std::_Index_tuple<0u>)	functional	1732	0x41184f	
  18. 17	std::_Bind_simple<Anchor::addDistanceValue(double)::__lambda2(double)>::operator()(void)	functional	1720	0x41173c	
  19. 18	std::thread::_Impl<std::_Bind_simple<Anchor::addDistanceValue(double)::__lambda2(double)> >::_M_run(void)	thread	115	0x4116a4	
  20. 19	libstdc++-6!execute_native_thread_routine	C:\Qt\5.3\mingw482_32\bin\libstdc++-6.dll		0xffe58f	
  21. 20	pthread_create_wrapper	C:\Qt\Tools\mingw482_32\opt\bin\libwinpthread-1.dll		0x64944e4b	
  22. 21	wtoi64	C:\Windows\SysWOW64\msvcrt.dll		0x759c0bc4	
  23. 22	msvcrt!_beginthreadex	C:\Windows\SysWOW64\msvcrt.dll		0x759c0cec	
  24. 23	KERNEL32!BaseThreadInitThunk	C:\Windows\SysWOW64\kernel32.dll		0x75e5919f	
  25. 24	ntdll!RtlInitializeExceptionChain	C:\Windows\SYSTEM32\ntdll.dll		0x77e8a8cb	
  26. 25	ntdll!RtlInitializeExceptionChain	C:\Windows\SYSTEM32\ntdll.dll		0x77e8a8a1	
  27. 26	??
To copy to clipboard, switch view to plain text mode