Hi!

I'm currently doing some experiments with signal handlers.
After some working examples I started with something more powerful:

Code: Select all

#include <stdlib.h>
#include <signal.h>
#include <iostream>
#include <stdexcept>
#include <pthread.h>

#include <QtCore>
#include <QtGui>
#include <QtDebug>
#include <QThreadStorage>

/*Define signal catching stuff */
using namespace std;

struct seg_error : public runtime_error
{
  int key;
  seg_error(string message = "", int _key = 0) : runtime_error(message), key(_key) {}
};

class LikePlasmoid : public QLabel
{
    Q_OBJECT
public:
    LikePlasmoid(const QString& text, QWidget *parent = 0) : QLabel(text, parent)
    {
        setWindowFlags(Qt::Window);
    }
};

class ThreadCrashPlasmoid : public LikePlasmoid
{
public:
    ThreadCrashPlasmoid(uint time) : LikePlasmoid("Crash after " + QString::number(time) + " seconds (separate thread)")
    {
        class Crasher : public QThread
        {
            uint time;
        public:
            Crasher(uint time, QObject *parent = 0) : QThread(parent), time(time)
            {
            }
            void run()
            {
                usleep(time);
                int *x = 0;
                qDebug() << *x;
            }
        };
        (new Crasher(time, this))->start();
    }
};

class EventCrashPlasmoid : public LikePlasmoid
{
public:
    EventCrashPlasmoid(uint time) : LikePlasmoid("Crash after " + QString::number(time) + " seconds (event thread)")
    {
        startTimer(time);
    }
protected:
    void timerEvent(QTimerEvent*)
    {
        int *x = 0;
        qDebug() << *x;
    }
};

class CrashFreeApp : public QApplication
{
    Q_OBJECT
public:
    static struct sigaction sa;
    static QThreadStorage<bool*> useHandler;
    static void fault(int key)
    {
        if(!useHandler.hasLocalData() || *useHandler.localData())
        {
            useHandler.setLocalData(new bool(false));
            QMessageBox *box = new QMessageBox(QMessageBox::Critical, QString("Error"), QString("This dialog should be replaced by DrKonqi!"), QMessageBox::Ok);
            box->setAttribute(Qt::WA_DeleteOnClose);
            box->show();
            throw seg_error("Segmentation Fault! Error key is: ", key);
        }
        else
            SIG_DFL(key);
    }
    static void installSignalHandlers()
    {
//         sa.sa_flags = SA_SIGINFO;
        sa.sa_flags = SA_NODEFER;
        sigemptyset(&sa.sa_mask);
        sa.sa_handler = fault;

        sigset_t mask;
        sigemptyset(&mask);
       
        #ifdef SIGSEGV
        sigaction(SIGSEGV, &sa, 0);
        sigaddset(&mask, SIGSEGV);
        #endif
        #ifdef SIGFPE
        sigaction(SIGFPE, &sa, 0);
        sigaddset(&mask, SIGFPE);
        #endif
        #ifdef SIGILL
        sigaction(SIGILL, &sa, 0);
        sigaddset(&mask, SIGILL);
        #endif
       
        pthread_sigmask(SIG_UNBLOCK, &mask, 0);
    }
    CrashFreeApp(int argc, char ** argv) : QApplication(argc,argv)
    {
        //Install signal handlers
        installSignalHandlers();
        //signal(SIGABRT, segmentationFault);
    }
    bool notify ( QObject * receiver, QEvent * event )
    {
        try
        {
            return QApplication::notify(receiver, event);
        }
        catch (seg_error & e)
        { //Catch possible crashes
            try
            {
                useHandler.setLocalData(new bool(true));
                cout << e.what() << endl;
                emit crashCatched(receiver, event, e);
            }
            catch(...)
            {
                useHandler.setLocalData(new bool(false));
                throw;
            }
        }
        return false;
    }

    Q_SIGNALS:
        void crashCatched(QObject*, QEvent*, seg_error&);
};

struct sigaction CrashFreeApp::sa;
QThreadStorage<bool*> CrashFreeApp::useHandler;

class LikeCorona : public QObject
{
    Q_OBJECT
public:
    LikeCorona() : QObject()
    {
        connect(qApp, SIGNAL(crashCatched(QObject*, QEvent*, seg_error&)), this, SLOT(processCrash(QObject *, QEvent *, seg_error&)), Qt::DirectConnection);
        LikePlasmoid *applet = new ThreadCrashPlasmoid(5);
        applet->resize(250, 150);
        applet->show();
        applet = new EventCrashPlasmoid(7);
        applet->resize(250, 150);
        applet->show();
        applet = new ThreadCrashPlasmoid(10);
        applet->resize(250, 150);
        applet->show();
        applet = new EventCrashPlasmoid(13);
        applet->resize(250, 150);
        applet->show();
    }

public slots:
    void processCrash(QObject * obj, QEvent * evt, seg_error& err) {
        //Handle the crash on the app itself
        qDebug() << "It crashed on" << obj << evt;
        if(LikePlasmoid *applet = qobject_cast<LikePlasmoid*>(obj))
        {
            qDebug() << "The receiver is a Plasmoid!";
            applet->deleteLater();
        }
        else
        {
            QObject *obj2 = QThread::currentThread()->parent();
            while(obj2 != 0)
            {
                if(LikePlasmoid *applet = qobject_cast<LikePlasmoid*>(obj2))
                {
                    qDebug() << "The thread is owned by a Plasmoid!";
                    applet->deleteLater();
                    return;
                }
            }
            qDebug() << "There were no Plasmoids, let's crash!!!!";
            throw err;
        }
    }

private:
};

int main(int argc, char ** argv)
{
        CrashFreeApp app(argc, argv);

        LikeCorona *likeCorona = new LikeCorona;

        return app.exec();
}

#include "likeplasmoid.moc"


The signal-handling is no problem (it worked nearly the same way with a simplier example) but I get strange runtime error, they are not reproducable, but it's always something with "QPixmap outside of GUI-Thread", "Cannot create children for parent that is in a different thread. (Parent is Oxygen...)", the application crashes with "X Error: BadPixmap" or "Fatal IO error". These faults happen before my experiments with null-pointers. (they should happen after at least 5 seconds) Any idea where I could break the GUI-thread?

Compilation:

Code: Select all

moc likeplasmoid.cpp > likeplasmoid.moc
g++ -o likeplasmoid likeplasmoid.cpp -funwind-tables -fnon-call-exceptions -fasynchronous-unwind-tables -I/usr/include/QtCore -I/usr/include/QtGui -lQtCore -lQtGui
./likeplasmoid

Thank you!

The User

Qt does not use Exceptions, which may lead to internal corruption, leading to failure of the GUI thread.

The runtime error occur before I throw any exceptions.

Edit:
Sorry, I forgot that setTimer takes the number of milliseconds.
Forget about this thread.

PPS:
It had nothing todo with exceptions: It was the QMessageBox...