Re: -persist and the wxWidgets terminal, continued

[<tim...@en...>]

Dave Denholm wrote:
> Timoth=E9e Lecomte <tim...@en...> writes:
>
>  =20
>> Dave Denholm wrote:
>>    =20
>>>> - mimic a 'bg' to gnuplot. Well, I don't know how to do that from
>>>> gnuplot, and I doubt it will actually work : since gnuplot's
>>>> process is still running, octave still waits for it.
>>>>
>>>> Do any of you have a miraculous idea, or should I report that to
>>>> the octave developers as I did for maxima ?
>>>>
>>>>
>>>>        =20
>>> gnuplot can fork(), then allow the parent to exit, leaving the child
>>> continuing to run the same code in exactly the same state, but
>>> detached.
>>>
>>>      =20
>> This won't work in my case, because the terminal is multithreaded and
>> fork() has undetermined behaviour with threads,
>>    =20
>
> Not really... you can install fork handlers (assuming pthreads). But
> yes, it all becomes horribly complicated. See pthread_atfork()
>  =20
Well, you're right, especially when you say "horribly complicated" ;)
>
>  =20
>> and because exiting
>> the parent would close file and socket descriptors, thus closing the
>> connection to the X server.
>>    =20
>
> No, the child inherits the open files.
>  =20
It does, but when the parent calls exit(), the corresponding files are=20
closed. There is a workaround : _exit(), but again, I think it becomes=20
too complicated and less portable.
>  =20
>> A workaround would be to close the GUI
>> thread and the windows before the fork() and to open them again in the
>> child, but I'm not sure maxima users would appreciate to see their
>> window disappearing and reappearing...
>>
>>    =20
>
>
> One other option would always be to immediately fork, but keep the
> parent around as a dummy process (just so that the original process
> knows it's still active). So all the work would happen in the child.
> In effect, code it as if you always detach, and then keep the parent
> alive as a workaround to stop the original process thinking the child
> has exited until the child chooses to detach.
>  =20
I wonder what happens regarding the command line then.

Anyway, I would *really* prefer not to have to play with fork() just to=20
satisfy a particular use case that is not written word for word=20
anywhere. I am sure the maxima folks will find a nice workaround=20
(there's already one workaround: defining a simple shell wrapper that=20
launches gnuplot in the background) (I would be glad to help them if=20
only it wouldn't be coded in lisp...).

Timoth=E9e