[osg-users] osgText crash with multiple Viewers

[Robert Osfield]

Hi Ravi,

My guess is that the new text implementation isn't the cause of the crash,
only it's the straw that broke the camels back, and actually there is an
underlying limitation with the OSG w..r.t you specific usage case.

Could you create a small test program that reproduces the crash.  Details
on your OS/dev tools/hardware will be useful too.

Cheers.
Robert.

On Tue, 18 Dec 2018 at 08:50, Ravi Mathur <ravidavi at utexas.edu> wrote:

> 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
> calls:
> - ~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.
>
> Thanks,
> Ravi
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