Re: ob-lilypond.el doesn't generate midi files

[Maxim Nikulin]

On 28/08/2021 02:54, Nick Dokos wrote:
> Also check if `org-babel-lilypond-arrange-mode' is t or nil: behavior
> is very different depending on that.
>
> Final thought: `xdg-open' starts whatever app it is supposed to run
> in the background and returns immediately. That may cause problems with
> babel.

To be precise, xdg-open is merely a wrapper. It does not decide whether 
a viewer should be started in background or in foreground, it just 
delegates decision concerning particular application and a way to start 
it to desktop environment (if any is running). Gnome's gio open and 
kde-open5 launch appropriate viewer in background. In my opinion they 
are free to do so.

It is a decade-old problem that emacs kills such processes. I disagree 
that it is e.g. Gnome bug.
https://lists.gnu.org/archive/html/emacs-devel/2009-07/msg00279.html

ob-lilypond.el suffers from this problem in its original form, and it 
should be fixed.

Approach taken in Org mode for compatibility reasons:
https://code.orgmode.org/bzg/org-mode/commit/869b7a21b94ed112f6640c8f2711c2a68b661dea
Emacs mailcap:
http://git.savannah.gnu.org/cgit/emacs.git/tree/lisp/net/mailcap.el#n1180

Pipe process instead of pty one is not a really robust way. The sour 
truth is that emacs API does allow reliable "shoot and forget" approach 
for external applications. Currently viewers might make Emacs CPU hungry 
for no reason (unsure if applications with such behavior exist in real 
world however). Eli Zaretskii suspects some incompatibility due to 
switching from pty to pipe processes, but he refused to provide details
https://debbugs.gnu.org/cgi/bugreport.cgi?bug=12972#38