kicad-developers team mailing list archive

[Maciej Sumiński <maciej.suminski@xxxxxxx>]

Hi Cirilo,

I am wondering whether it really solves the problem. C++ standard ([1],
5.3.5.2) explicitly permits null pointer to be an argument for delete,
so it should not crash there.

I am afraid the problem might be a bit more entangled. Mario & me have
already noticed a few cases when an OpenGL context switch occurs before
a destructor is called, and as the result OpenGL resources are being
freed in a wrong OGL context.

It happens because wxWidgets does not permit setting OpenGL context when
the parent window is invisible [2]. The second reason is delayed
wxDialog destruction [3], so we cannot control when it exactly happens,
and almost surely the destructor will be called when the window is
already invisible. Due to that, the following might happen (Mario has
discovered it):

1. Display a modal dialog with a OpenGL canvas that uses a different context
2. Switch OpenGL context to the just created canvas
3. Close the modal dialog (it is not destructed yet)
4. Return to pcbnew, switch OpenGL context to GAL
5. The dialog destructor is called - officially you cannot switch the
context now, as the dialog is invisible, so you are stuck in the GAL OGL
context. Freeing OGL resources allocated in the dialog will fail,
because it is a wrong context.

For the moment I do not have any good ideas how to solve the problem in
a clear way.

Regards,
Orson

1. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3242.pdf
2.
http://docs.wxwidgets.org/stable/classwx_g_l_canvas.html#a9f9ab3909606484e717904064d4e7b4f
3.
http://docs.wxwidgets.org/trunk/overview_windowdeletion.html#overview_windowdeletion_sequence

On 05/23/2016 11:35 PM, Cirilo Bernardo wrote:
> The attached patch fixes bug #1572567 (crash on exit from
> 3D Footprint Properties dialog). Since there was no check
> before deleting m_ogl_3dmode, delete can be called on
> NULL.
> 
> - Cirilo
> 
> 
> 
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