[Octave-bug-tracker] [bug #47958] GUI freezes when starting debug with a partly drawn Qt figure

[Lachlan Andrew]

URL:
  <http://savannah.gnu.org/bugs/?47958>

                 Summary: GUI freezes when starting debug with a partly drawn
Qt figure
                 Project: GNU Octave
            Submitted by: lachlan
            Submitted on: Thu 19 May 2016 11:24:20 AM GMT
                Category: Plotting with OpenGL
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Crash
                  Status: None
             Assigned to: None
         Originator Name: Lachlan
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: dev
        Operating System: GNU/Linux

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Details:

When running from the GUI, the code


debug_on_error (1);
a.one = 1;
a.two = 2;
imagesc (a);


causes the GUI to hang, requiring ^C from the lauching terminal or "force
quit" from the window manager.  (Is "crash" the right item group for this?)

Running under gdb gives the following unhelpful stack trace:


Program received signal SIGINT, Interrupt.
0x00007ffff6c6adba in __libc_waitpid (pid=16829, stat_loc=0x7fffffffd160, 
    options=0) at ../sysdeps/unix/sysv/linux/waitpid.c:31
31      ../sysdeps/unix/sysv/linux/waitpid.c: No such file or directory.
(gdb) thread apply all bt

Thread 1 (Thread 0x7ffff7fd0780 (LWP 16825)):
#0  0x00007ffff6c6adba in __libc_waitpid (pid=16829, stat_loc=0x7fffffffd160,

    options=0) at ../sysdeps/unix/sysv/linux/waitpid.c:31
#1  0x000000000040194d in main (argc=<optimized out>, argv=<optimized out>)
    at src/main.cc:560


This doesn't occur with FLTK or gnuplot.

If it is run with --no-gui, then the interpreter remains responsive, but the
figure window seems to hang (it doesn't redraw on expose events) until debug
mode is exited.  After that, it returns to normal.

With "dbstop image 201", i.e., the line


h = __go_image__ (hax, "cdata", img, "xdata", xdata, "ydata", ydata,
                         "cdatamapping", "direct", varargin{:});


running these commands and then typing "dbcont" doesn't cause the freeze.  I
thought it may have something to do with the redraw caused by going to the
prompt, but putting an explicit "drawnow" before that line doesn't help. 
Perhaps it is a timing issue -- however it is more reproducible than I'd
expect from a race condition.




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