[Octave-bug-tracker] [bug #48519] Segfault with Qt plotting when running demos

[Andreas Weber]

Follow-up Comment #2, bug #48519 (project octave):

Hi Lachlan. Your patch clearly avoids the segfault but it looks to me like a
workaround for a deeper problem.

The problem is triggered if the previous parameters are restored after
"print". I've added some debug output to stdout


diff -r 3f8ed6d7cb1c libgui/graphics/ObjectProxy.cc
--- a/libgui/graphics/ObjectProxy.cc    Sat Jul 16 17:49:30 2016 +0200
+++ b/libgui/graphics/ObjectProxy.cc    Sun Jul 17 14:06:02 2016 +0200
@@ -43,6 +43,7 @@
 void
 ObjectProxy::init (Object* obj)
 {
+  std::cout << "ObjectProxy::init obj=" << obj << " m_object=" << m_object <<
std::endl;
   if (obj != m_object)
     {
       if (m_object)
@@ -83,6 +84,8 @@
 void
 ObjectProxy::update (int pId)
 {
+  std::cout << "ObjectProxy::update pId=" << pId << " m_object=" << m_object
<< std::endl;
+
   if (octave_thread::is_octave_thread ())
     emit sendUpdate (pId);
   else


which gives before the segfault:


ObjectProxy::init obj=0 m_object=0
ObjectProxy::update pId=2053 m_object=0
ObjectProxy::update pId=2055 m_object=0
ObjectProxy::update pId=2056 m_object=0
ObjectProxy::update pId=2005 m_object=0
ObjectProxy::init obj=0x25a3c60 m_object=0
ObjectProxy::update pId=2046 m_object=0x25a3c60
ObjectProxy::update pId=2047 m_object=0x25a3c60
ObjectProxy::update pId=2048 m_object=0x25a3c60
ObjectProxy::update pId=2049 m_object=0x25a3c60
Printing "axis_08.png" ... ObjectProxy::update pId=2030 m_object=0x25a3c60
ObjectProxy::update pId=2030 m_object=0x25a3c60
[0.295166 0.556593] done
ObjectProxy::update pId=0 m_object=0x25a3c60
ObjectProxy::init obj=0 m_object=0x25a3c60
ObjectProxy::init obj=0 m_object=0
ObjectProxy::update pId=2053 m_object=0
ObjectProxy::update pId=2055 m_object=0
ObjectProxy::update pId=2056 m_object=0
ObjectProxy::update pId=2046 m_object=0


I'm doubt it's in intended that ObjectProxy::init ist called with both obj=0
and m_object=0. This whole QtHandles backend is a unfathomable beast for me...

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