[Octave-bug-tracker] [bug #53802] octave deadlocks with deletefcn callback that calls graphical function

[Dan Sebald]

Follow-up Comment #2, bug #53802 (project octave):

We addressed something similar to this in the past, but I think that was
merely a simple C++ fix:

https://savannah.gnu.org/bugs/?func=detailitem&item_id=52666

However, Rik is probably correct here.

To explain the freeze, keep in mind that the hand-shaking for the Qt input
dialog class of functions is programmed to put the worker thread to sleep when
the user is engaged in responding to the dialog box.  That was my crude way of
doing thread-safe sequential programming when at the time the Qt input dialog
class was added there was no designed cross-thread protocol.

So, what could be happening is that the figure-closing graphics operations are
interfering with the display of the question-dialog.  Rather than freezing,
think of this one as Octave core (worker thread) waiting for the user to
answer a question when there is no dialog box and button to click showing on
the screen.

Notice the CPU monitor shows ostensibly 0% whereas for a freeze there is
typically some sort of infinite loop with 100% CPU usage.

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