X widget question

Jon Turney jon.turney@dronecode.org.uk
Tue Mar 22 10:19:00 GMT 2016

On 20/03/2016 09:57, Marco Atzeri wrote:
> I have finally identified where ncview was
> segfaulting on X86_64
> The solution was to reverse the order of destruction
> for a chain of widgets

Nice to see that you have resolved this.

It's not clear from what you write if you are sure there is an 
undocumented ordering constraint (which just happens to not crash on 
32-bit), or if reversing the ordering just happens to make things not 
crash on 64-bit

> The segfault was inside Xlib when managing the constraints.
> As the segfault did not happened on i686, is it possible
> that is a race inside Xlib  ?
> I have not found in the X Documentation nothing about
> requested order of widget destruction in this case.

Possible, yes.  It seems more likely that there is a documentation 
error, or a bug in handling widgets which share a constraint being 
destroyed out of order.

I'm afraid finding someone who cares greatly about libXt will be hard, 
but do you think it would now be possible to craft a test case which 
demonstrates the problem?

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