SOFA closes unexpectedly when removing and adding again an object in the simulation, while looking at it in the GUI

[itsmebonny]

Hi everyone,

I am using Ubuntu 22.04.4 and SOFA 23.12.01 (the precompiled binary available on the website).

I'm trying to run a simple beam deforming under a load and encountered a weird bug. Since the load applied changes every timestep, I need to know which force is applied. To do so, I tried opening the ConstantForceField window in the GUI of Sofa. The problem is that when the ConstantForceField window is open, when I run the next step of the simulation, SOFA crashes and throws a segmentation fault error.

I think the problem is due to the fact that I'm removing the ConstantForceField object in the simulation and replacing it with a new one. In fact, if I do not replace the object, but only remove it, the simulation keeps running with no problems (sorry for the long code, it was the minimal working example that I was able to produce).

import Sofa
import SofaRuntime
from Sofa import SofaDeformable
from time import process_time, time


class AnimationStepController(Sofa.Core.Controller):
    def __init__(self, node, *args, **kwargs):
        Sofa.Core.Controller.__init__(self, *args, **kwargs)
        self.externalForce = [0, -10, 0]
        self.createGraph(node)
        self.root = node
        self.save = False

    def createGraph(self, rootNode):

        
        plugins = ['Sofa.Component.Constraint.Projective',
            'Sofa.Component.Engine.Select',
            'Sofa.Component.LinearSolver.Iterative',
            'Sofa.Component.LinearSolver.Direct',
            'Sofa.Component.Mass',
            'Sofa.Component.Mapping.Linear',
            'Sofa.Component.MechanicalLoad',
            'Sofa.Component.ODESolver.Backward',
            'Sofa.Component.SolidMechanics.FEM.Elastic',
            'Sofa.Component.StateContainer',
            'Sofa.Component.Topology.Container.Dynamic',
            'Sofa.Component.Topology.Container.Grid',
            'Sofa.Component.Visual',
            'MultiThreading']
        rootNode.addObject('RequiredPlugin', pluginName=plugins)


        rootNode.addObject('DefaultAnimationLoop')
        rootNode.addObject('DefaultVisualManagerLoop')
        rootNode.addObject('VisualStyle', name="visualStyle", displayFlags="showBehaviorModels showCollisionModels")
        

        self.LowResSolution = rootNode.addChild('LowResSolution2D', activated=True)
        self.LowResSolution.addObject('RegularGridTopology', n="50 10 1", min="0 -1 0", max='10 1 0', name='grid')
        self.LowResSolution.addObject('TriangleSetTopologyContainer', name='quadTopo', src='@grid')
        self.MO2 = self.LowResSolution.addObject('MechanicalObject', name='DOFs', template='Vec3d', src='@grid')
        self.LowResSolution.addObject('StaticSolver', name='ODE', newton_iterations="20", printLog=False)
        self.LowResSolution.addObject('CGLinearSolver', iterations=250, name="linear solver", tolerance="1.0e-6", threshold="1.0e-6")
        self.LowResSolution.addObject('TriangularFEMForceField', name="FEM", youngModulus=5000, poissonRatio=0.4, method="large")
        self.LowResSolution.addObject('BoxROI', name='ROI', box='-0.1 -2.1 -2.1 0.1 2.1 2.1')
        self.LowResSolution.addObject('FixedConstraint', indices='@ROI.indices')
        self.LowResSolution.addObject('BoxROI', name='ROI2', box='9.9 -1.1 -1.1 10.1 2.1 1.1')
        self.cffLR = self.LowResSolution.addObject('ConstantForceField', indices="@ROI2.indices", totalForce=self.externalForce, showArrowSize=0.1, showColor="0.2 0.2 0.8 1")

        self.LowResSolution.addChild("visual")
        self.LowResSolution.visual.addObject('OglModel', src='@../grid', color='1 0 0 0.2')
        self.LowResSolution.visual.addObject('IdentityMapping', input='@../DOFs', output='@./')


    def onAnimateBeginEvent(self, event):

        # reset positions
        self.MO2.position.value = self.MO2.rest_position.value

        # here we remove the old constant force field and add a new one
        self.LowResSolution.removeObject(self.cffLR)

        # if these two lines are commented out, the bug does not occur
        self.cffLR = self.LowResSolution.addObject('ConstantForceField', indices="@ROI2.indices", totalForce=self.externalForce, showArrowSize=0.1, showColor="0.2 0.2 0.8 1")
        self.cffLR.init()

   

def createScene(rootNode, *args, **kwargs):
    rootNode.dt = 0.01
    rootNode.gravity = [0, 0, 0]
    rootNode.name = 'root'
    asc = AnimationStepController(rootNode, *args, **kwargs)
    rootNode.addObject(asc)
    return rootNode, asc


def main():
    import Sofa.Gui
    SofaRuntime.importPlugin("Sofa.GL.Component.Rendering3D")
    SofaRuntime.importPlugin("Sofa.GL.Component.Shader")
    SofaRuntime.importPlugin("Sofa.Component.StateContainer")

    root=Sofa.Core.Node("root")
    createScene(root)
    Sofa.Simulation.init(root)

    Sofa.Gui.GUIManager.Init("myscene", "qglviewer")
    Sofa.Gui.GUIManager.createGUI(root, __file__)
    Sofa.Gui.GUIManager.SetDimension(800, 600)
    Sofa.Gui.GUIManager.MainLoop(root)
    Sofa.Gui.GUIManager.closeGUI()


if __name__ == '__main__':
    main()

Once this script is launched, in the GUI, go to root > LowResSolution2D > ConstantForceField in the GUI and double click to open it. Once the window is open, press the Animate button and SOFA should crash with this error

########## SIG 11 - SIGSEGV: segfault ##########
  sofa::helper::BackTrace::sig(int)
  sofa::core::objectmodel::DDGNode::updateIfDirty() const
  sofa::gui::qt::SimpleDataWidget<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, sofa::gui::qt::data_widget_container<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > >::readFromData()
  sofa::gui::qt::DataWidget::updateWidgetValue()
  QMetaObject::activate(QObject*, int, int, void**)
  QMetaObject::activate(QObject*, int, int, void**)
  QMetaObject::activate(QObject*, int, int, void**)
  sofa::gui::qt::ModifyObject::updateTables()
  sofa::gui::qt::QSofaListView::UpdateOpenedDialogs()
  QMetaObject::activate(QObject*, int, int, void**)
  sofa::gui::qt::RealGUI::step()
  QMetaObject::activate(QObject*, int, int, void**)
  QTimer::timeout(QTimer::QPrivateSignal)
  QTimer::timerEvent(QTimerEvent*)
  QObject::event(QEvent*)
  QApplicationPrivate::notify_helper(QObject*, QEvent*)
  QApplication::notify(QObject*, QEvent*)
  QCoreApplication::notifyInternal2(QObject*, QEvent*)
  QTimerInfoList::activateTimers()
  g_main_context_dispatch
  g_main_context_iteration
  QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>)
  QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>)
  QCoreApplication::exec()
  sofa::gui::qt::RealGUI::mainLoop()
  sofa::gui::common::GUIManager::MainLoop(boost::intrusive_ptr<sofa::simulation::Node>, char const*)
  _PyObject_MakeTpCall
  _PyEval_EvalFrameDefault
  _PyFunction_Vectorcall
  _PyEval_EvalFrameDefault
  PyEval_EvalCode
  _PyRun_SimpleFileObject
  _PyRun_AnyFileObject
  Py_RunMain
  Py_BytesMain
  __libc_start_main
  _start
Segmentation fault (core dumped)

I wanted to try and reproduce the error using this example from SofaPython3's repository, but launching it on my machine as is throws a segmentation fault error. I hope to solve it and come back with an example in that case. In the meantime this code should be enough to reproduce this error.

[hugtalbot]

Hi @itsmebonny

Clearly the Qt GUI of SOFA has not been thought years ago to manage the case of deleted components in the graph.
I notify some devs here @alxbilger @damienmarchal

FYI we are in the process of updated the GUI, efforts would rather be put on making sure this behavior does not appear in the ImGUI-based GUI