Re: segfaults building documentation when machine under load

On 5/19/20 4:11 PM, Dmitri A. Sergatskov wrote:
> 
> 
> On Tue, May 19, 2020 at 4:02 PM John W. Eaton <[email protected] 
> <mailto:[email protected]>> wrote:
> 
>     On 5/19/20 3:26 PM, Dmitri A. Sergatskov wrote:
> 
>      >     Should we switch to bug-tracker?
>      >     I was able to get a crash when I bumped the jobs to 200.
>      >     bt is attached. The relevant part seems to be:
> 
>     If I use a large number of jobs, I see
> 
>         error: imwrite: invalid empty image
>         error: called from
>             __imwrite__ at line 40 column 5
>             imwrite at line 125 column 5
>             print at line 755 column 13
>             interpimages at line 72 column 5
> 
>     but no segfaults.
> 
>     It does look like a threading issue.
> 
> 
> I used a simplified test by Andreas:
> 
> parallel -N0 -q octave --norc --silent --no-history --eval 'figure 
> (1,"visible", "off");' ::: {1..200}

OK, I'm able to duplicate the problem using this method.

In the stack traces I've seen, Octave is crashing inside the interpreter 
object destructor while attempting to close any remaining figures.

Changing the eval above to be

   figure (1, "visible", "off"); close ("all"); pause (1);

eliminates the crash for me, apparently because then there are no figure 
windows to close when exiting.  But attempting the same thing in the 
doc/interpreter scripts that generate plots I see the "invalid empty 
image" error on every attempt to create a figure, at least when using a 
large number of parallel Make jobs.

So clearly this kind of change is not a solution, but it may point us 
toward one.  Ultimately, we need to determine the correct sequence for 
shutting down the GUI and interpreter, including what actions can happen 
or need to be blocked, and what signals need to be sent or locks 
acquired so that there are no more races between the threads.

It's a bit tricky because figures can have callbacks set to run when the 
figure is closed.  Do we expect those to run when Octave is in the 
process of exiting or is it OK to skip them?  Those functions could 
register code to run when Octave exits.  Should that be possible?  Would 
it be OK for an atexit function to display a graph?  What is reasonable 
to expect or attempt to do?

jwe