Memory corruption related to signal emission?

[amleto]

right, so have you debugged the values of streamOneSSRC, and the array value at that index?

[blooglet]

I should probably mention that _streams is a QMap. streamOneSSRC and streamTwoSSRC are uint32_t with values similar to 738621152 and 3435571404. I've asserted that

assert(_streams.find(streamOneSSRC) != _streams.end());
        assert(_streams.find(streamTwoSSRC) != _streams.end());

assert(_streams.find(streamOneSSRC) != _streams.end());
        assert(_streams.find(streamTwoSSRC) != _streams.end());

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right before the signal emission happens.

[stampede]

Why do you think this is related to signal emission, and not to accessing the QMap ?
Does it crash if you just print the values ?

// emit newStreamFound(_streams[streamOneSSRC]);
// emit newStreamFound(_streams[streamTwoSSRC]);
qDebug() << _streams[streamOneSSRC];
qDebug() << _streams[streamTwoSSRC];

// emit newStreamFound(_streams[streamOneSSRC]);
// emit newStreamFound(_streams[streamTwoSSRC]);
qDebug() << _streams[streamOneSSRC];
qDebug() << _streams[streamTwoSSRC];

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[blooglet]

Nope, that seems to work just fine.

VideoStream(0x7fffe4110e20) 
VideoStream(0x7fffe4110e90)

VideoStream(0x7fffe4110e20) 
VideoStream(0x7fffe4110e90)

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But then again if I'm dealing with a memory corruption bug this behavior could be undefined.

[amleto]

how are you pasing the data through the signaal/slot? const ref?

[blooglet]

By pointer.

void newStreamFound(VideoStream*);

void newStreamFound(VideoStream*);

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_streams is a QMap<uint32_t, VideoStream*>.

[amleto]

you've got a problem somewhere else then. emitting a signal with a pointer as an argument, and with no slots connected, does not cause a seg fault.

[blooglet]

Right... so it's likely to be memory corruption like I thought then? Can you conclude anything from the Valgrind memory analysis about where the error might be?

[amleto]

seg fault is always doing something dodgy to memory isnt it?

valgrind doesnt play too nicely with qt from what little I have read about it so not sure you can conclude much from it.

[stampede]

Build debug version, launch with debugger and examine (post here) backtrace after crash.

[blooglet]

I got this from gdb.

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff711000c in ?? () from /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtGui.so.4
(gdb) backtrace
#0 0x00007ffff711000c in ?? () from /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtGui.so.4
#1 0x00007ffff711101a in QPainter::QPainter(QPaintDevice*) () from /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtGui.so.4
#2 0x00007ffff73fdb3d in QFrame::paintEvent(QPaintEvent*) () from /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtGui.so.4
#3 0x00007ffff701325b in QWidget::event(QEvent*) () from /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtGui.so.4
#4 0x00007ffff73fd7cb in QFrame::event(QEvent*) () from /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtGui.so.4
#5 0x00007ffff6fb2faf in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtGui.so.4
#6 0x00007ffff6fb9c8b in QApplication::notify(QObject*, QEvent*) () from /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtGui.so.4
#7 0x00007ffff6a62dc4 in QCoreApplication::notifyInternal(QObject*, QEvent*) () from /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtCore.so.4
#8 0x00007ffff700d202 in QWidgetPrivate::drawWidget(QPaintDevice*, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*) () from /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtGui.so.4
#9 0x00007ffff700dd32 in QWidgetPrivate::paintSiblingsRecursive(QPaintDevic e*, QList<QObject*> const&, int, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*) ()
from /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtGui.so.4
#10 0x00007ffff700cf7f in QWidgetPrivate::drawWidget(QPaintDevice*, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*) () from /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtGui.so.4
#11 0x00007ffff71ebf6a in ?? () from /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtGui.so.4
#12 0x00007ffff7004086 in QWidgetPrivate::syncBackingStore() () from /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtGui.so.4
#13 0x00007ffff7013911 in QWidget::event(QEvent*) () from /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtGui.so.4
#14 0x00007ffff741a4e1 in QMainWindow::event(QEvent*) () from /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtGui.so.4
#15 0x00007ffff6fb2faf in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtGui.so.4
#16 0x00007ffff6fb9c8b in QApplication::notify(QObject*, QEvent*) () from /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtGui.so.4
#17 0x00007ffff6a62dc4 in QCoreApplication::notifyInternal(QObject*, QEvent*) () from /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtCore.so.4
#18 0x00007ffff6a63ef1 in QCoreApplicationPrivate::sendPostedEvents(QObject* , int, QThreadData*) () from /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtCore.so.4
#19 0x00007ffff6a90703 in ?? () from /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtCore.so.4
#20 0x00007ffff553da5d in g_main_context_dispatch () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#21 0x00007ffff553e258 in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#22 0x00007ffff553e429 in g_main_context_iteration () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#23 0x00007ffff6a90a1c in QEventDispatcherGlib::processEvents(QFlags<QEventL oop::ProcessEventsFlag>) () from /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtCore.so.4
#24 0x00007ffff7065c0f in ?? () from /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtGui.so.4
#25 0x00007ffff6a62115 in QEventLoop::processEvents(QFlags<QEventLoop::Proce ssEventsFlag>) () from /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtCore.so.4
#26 0x00007ffff6a62366 in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsF lag>) () from /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtCore.so.4
#27 0x00007ffff6a641a4 in QCoreApplication::exec() () from /opt/QtSDK/Desktop/Qt/474/gcc/lib/libQtCore.so.4
#28 0x000000000040781f in launchGUI (ip=0x7fffffffe3c6 "127.0.0.1", port=12000) at ../VideoStreamer/main.cpp:36
#29 0x0000000000407795 in main (argc=3, argv=0x7fffffffe068) at ../VideoStreamer/main.cpp:27

[stampede]

Can you post the code for launchGUI (or maybe whole main.cpp) ?