Re: Debugging output

[Daniel J Sebald]

On 01/30/2016 04:53 PM, LachlanA wrote:
> Greetings all,
>
> I find it hard to debug crashes of GUI behaviour because  stderr  is
> redirected to the GUI, which disappears on the crash.  Does anyone else have
> the same problem?  If so, how do you overcome it?

From what I remember, the stderr/stdout/signal handling is a delicate 
thing in the GUI/core setup.  There were several bug/patch reports along 
the way, but I don't think an acceptable solution ever emerged.


> If there is no simple work-around, I'd suggest that stderr still go to the
> console, even if it is also sent to the GUI.  Would that behaviour be
> acceptable?

Try it, but it might have side effects like cntrl-C not working correct 
or whatnot.  My guess is you won't find a quick fix, although an 
in-depth fix might be possible.  But there are multiple platforms to 
consider, so...


> Also, I find that I often want a stack trace after a crash.  Since crashes
> should be rare, and stack traces are small, I think there is a case for
> always trying to output a stack trace from the signal handler.  I know that
> the recommended approach is to use gdb, which seems fine for the CLI, but
> running "bt" in gdb doesn't give the stack trace of the GUI thread.  This
> behaviour could be disabled for the releases if you think the general public
> wouldn't like it, but I think it would be useful to have in the development
> branch.
>
> Thoughts?

Search around the Qt documentation for "qt debugging techniques", or 
"qDebug", and such.  Maybe that will help.

Dan