[Octave-bug-tracker] [bug #57319] legend() fails after being repeadetly called (show/off) after plotyy

[Pantxo Diribarne]

Follow-up Comment #10, bug #57319 (project octave):

@Rik: Pause was not meant to introduce a delay, but rather to force processing
graphics events. I still cannot reproduce the "execution error ..." but after
playing with plotyy in uipanel I can confirm that processing graphics events
is not enough to avoid infinite execution of callbacks. I think the base
problem boils down to the following example:


figure (567); clf;
hp = uipanel ();
hax = axes ("parent", hp);

function updater (h, ~)
  persistent updating = false;
  if (! updating)
    units  = get (h, "units");
    updating = true;
    unwind_protect
      disp updating
      set (h, "units", "points", "units", units)
    unwind_protect_cleanup
      ## pause (0.01) # process events
      updating = false;
    end_unwind_protect
  endif
endfunction

addlistener (hax, "tightinset", @updater)
addlistener (hax, "position", @updater)

set (gcf(), 'position', [50 50 350 315]);


The above script results in an infinite series of callback execution. Since
this is not recursive, the "updating" variable is always false and we cannot
do anything to stop the execution (except closing the figure with the X
button). Without the uipanel, the above is properly stabilized by the
"updating" variable. 

Now adding the pause and increasing the time laps increases the probability of
stopping the execution but this is clearly unreliable.

Fixing this properly now looks like much work than I had foreseen. 

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