On Thu, Apr 7, 2022 at 11:11 PM Jérôme LAURENS <jerome.laurens@u-bourgogne.fr> wrote:

Le 7 avr. 2022 à 22:53, luigi scarso <luigi.scarso@gmail.com> a écrit :

On Thu, Apr 7, 2022 at 9:30 PM Jérôme LAURENS <jerome.laurens@u-bourgogne.fr> wrote:
Yes, this does work on a per document basis, but what I request is a builtin feature that simply applies out of the box and is backwards compatible.

 it's not  clear what you want to achieve.... What does "busy" mean in this context ?

It means that the output file is named jobname.pdf despite it is known to be incomplete and unusable during all the typesetting process.
The output file should be named jobname.pdf only once it is really a complete pdf file.
In the meanwhile its extension is pdf(busy), which means that it is a pdf file under construct.

It's a well established rule that one can use the file jobname.pdf *after* that the luatex process ends, and even in this case it doesn't mean that 
the pdf is complete and / or usable , even if the luatex process ends correctly.