[Octave-bug-tracker] [bug #45469] Program execution stops unpredictably with error in plot statement

[Dan Sebald]

Follow-up Comment #3, bug #45469 (project octave):

It's the Qt toolkit, for sure.  I haven't seen a problem, not yet anyway, for
FLTK or gnuplot.  I'm attaching a simple for-loop that plots random data. 
Start Octave GUI (change the graphics toolkit if you like to something other
than qt if you are curious whether those fail) then run "plot_loop".  I
eventually run into the error described by the bug report.


>> plot_loop
error: octave_base_value::convert_to_str_internal (): wrong type argument
'<unknown type>'
error: called from
    __line__ at line 117 column 21
    line at line 56 column 8
    __plt__>__plt2vv__ at line 500 column 10
    __plt__>__plt2__ at line 246 column 14
    __plt__ at line 113 column 17
    plot at line 220 column 10
    plot_loop at line 4 column 3
[repeated six times]


I've also had the GUI crash and disappear with the following signal:

[sebald@ octave]$ octave exited with signal 6

If after a half dozen tries everything seems fine, start the loop again and
then grab the gui window and drag it over the Qt plot while the loop is
processing.  That Qt redraw action is probably causing the conflict.

If one removes the comment character from before the pause(0), the loop
doesn't seem to cause problems.  Or at least it is far less likely to, as I
haven't seen it fail in that case.

The error message comes about because the
octave_base_value::convert_to_str_internal () is supposed to be overridden by
a derivative object, not run from the base class.  Some octave_value object
without a defined overriding function is being called.  But I'm not sure if
that is precisely what is happening, or instead maybe the code simply goes off
course there.  I think this comes back to the similar issue seen previously
with Qt plotting and thread management.

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