[osg-users] Alter tree in safe mode.

[Dario Minieri]

Hi,

I have a system which use an UpdateCallback for every node which can be modified (adding or removing his children).  Sometime I have segmentation fault inside the callback, like this one:

#0  0x00007ffff4b02cc9 in __GI_raise (sig=sig at entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56
#1  0x00007ffff4b060d8 in __GI_abort () at abort.c:89
#2  0x00007ffff5107535 in __gnu_cxx::__verbose_terminate_handler() () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#3  0x00007ffff51056d6 in ?? () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#4  0x00007ffff5105703 in std::terminate() () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#5  0x00007ffff5105922 in __cxa_throw () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#6  0x00007ffff5105e0d in operator new(unsigned long) () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#7  0x00007ffff0e83ac6 in std::vector<osg::Group*, std::allocator<osg::Group*> >::_M_insert_aux(__gnu_cxx::__normal_iterator<osg::Group**, std::vector<osg::Group*, std::allocator<osg::Group*> > >, osg::Group* const&) () from /usr/local/lib/libosg.so.100
#8  0x00007ffff0e83266 in osg::Node::addParent(osg::Group*) () from /usr/local/lib/libosg.so.100
#9  0x00007ffff0e14bad in osg::Group::insertChild(unsigned int, osg::Node*) () from /usr/local/lib/libosg.so.100
#10 0x00007ffff488501f in AlterTreeNodeCallback::operator()(osg::Node*, osg::NodeVisitor*) () from /usr/local/lib/libSimWorld.so
#11 0x00007ffff0e150b2 in osg::Group::accept(osg::NodeVisitor&) () from /usr/local/lib/libosg.so.100
#12 0x00007ffff0e13af3 in osg::Group::traverse(osg::NodeVisitor&) () from /usr/local/lib/libosg.so.100
#13 0x00007ffff0e150b2 in osg::Group::accept(osg::NodeVisitor&) () from /usr/local/lib/libosg.so.100
#14 0x00007ffff0e13af3 in osg::Group::traverse(osg::NodeVisitor&) () from /usr/local/lib/libosg.so.100
#15 0x00007ffff0e150b2 in osg::Group::accept(osg::NodeVisitor&) () from /usr/local/lib/libosg.so.100
#16 0x00007fffeff514a1 in osgViewer::Viewer::updateTraversal() () from /usr/local/lib/libosgViewer.so.100
#17 0x00007fffeff5b685 in osgViewer::ViewerBase::frame(double) () from /usr/local/lib/libosgViewer.so.100
#18 0x00007ffff04356e4 in QGLWidget::glDraw() () from /usr/lib/x86_64-linux-gnu/libQt5OpenGL.so.5
#19 0x00007ffff04326f9 in QGLWidget::paintEvent(QPaintEvent*) () from /usr/lib/x86_64-linux-gnu/libQt5OpenGL.so.5
#20 0x00007ffff5521302 in QWidget::event(QEvent*) () from /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
#21 0x00007ffff54e5c8c in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
#22 0x00007ffff54eae56 in QApplication::notify(QObject*, QEvent*) () from /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
#23 0x00007ffff6488c2d in QCoreApplication::notifyInternal(QObject*, QEvent*) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#24 0x00007ffff551bbea in QWidgetPrivate::drawWidget(QPaintDevice*, QRegion const&, QPoint const&, int, QPainter*, QWidgetBackingStore*) ()
   from /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
  
Adding (insertChild) some new node at runtime, show the problem. This happens especially when I made some remove and insert in short time.

The callback is something like this:


Code:
void AlterCallback::operator()(Node* p_node, NodeVisitor* p_nv) {
  if (p_node != NULL) {
    Group* p_group = p_node->asGroup();
    if (p_group != NULL) {
      while (m_add_nodes.size() > 0) {
          Node* l_node = (Node*)m_add_nodes.popFront();
          p_group->addChild(l_node);
        }

      while (m_remove_nodes.size() > 0) {
        Node* l_node = (Node*)m_remove_nodes.popFront();
        p_group->removeChild(l_node);
      }
    }
    
    traverse(p_node, p_nv);
  }
}



m_add_nodes and m_remove_nodes are thread-safe structures which holds the list of nodes (pointers) to add and remove. 

This is a good way to alter the tree at runtime?

Thank you!

Cheers,
Dario

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