[osg-users] osgText crash with multiple Viewers

Ravi Mathur ravidavi at utexas.edu
Tue Dec 18 00:50:01 PST 2018

Hello all,

I'm seeing a crash on the OpenSceneGraph-3.6 branch that occurs when I have
two CompositeViewers that contain Text objects in their scenes. My
simplified scenario is this:
- 2 CompositeViewers, each in singlethreaded mode, but being run at the
same time in separate threads (via OpenThreads::Thread wrappers)
- The viewers do not share scenes or contexts, and each has a single Text
object as its scene
- Each viewer is destroyed immediately after its run() loop returns (needed
for my application)

Both viewers animate just fine in their own windows. The crash happens if
one viewer is being destroyed while the other is actively rendering. Note
that it only seems to crash if there are Text objects in each scene, and
did not crash with the old (pre-3.6) Text implementation.

Is this usage model ok in the first place? Robert, I read your post in this
recent thread <http://forum.openscenegraph.org/viewtopic.php?t=16844> in
which you advise against manually destroying viewers. Should I assume that
I was just lucky in getting away with this until now? The new Text
implementation seems to be the only thing that triggers the crash.

In case anybody is interested, the crash happens due to this sequence of
- ~CompositeViewer() calls GraphicsContext::close(), which deletes its State
- ~CompositeViewer() then destroys its osgViewer::View, which in turn
destroys its Camera
- ~Camera() eventually calls osgText::releaseGLObjects() with a null State.
- osgText::releaseGLObjects(null) deletes text-related objects (Programs)
on ALL contexts
- The other CompositeViewer, which is actively rendering its Text on
another context, crashes with an access violation since its Text-related
Programs were just deleted.

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