Re: [Bug] Unexpected process suspension

[Stephane Chazelas <stephane@chazelas.org>]

2020-05-12 10:38:38 -0700, Bart Schaefer:
> On Tue, May 12, 2020 at 12:03 AM Rudi C <rudiwillalwaysloveyou@gmail.com> wrote:
> >
> > mdoc-test () {
> >
> >     sleep 0 | sleep 0
> >     cat}
> >
> > echo start |VISUAL=vim command vipe|mdoc-test
> >
> > # zsh: suspended (tty output)
> 
> Putting an interactive command in the middle of a pipeline is
> generally not going to work.  Vim in particular is pretty aggressive
> about trying to grab a terminal, which will result in processes
> getting SIGTT* because they don't have foreground control of the
> terminal they're trying to use.
[...]

The thing is vim *should* be in the foreground, all the
processes started in pipeline should be in the same process
group which should be in foreground (so it gets
SIGINT/SIGQUIT/SIGTSTP upon ^C/^\/^Z, so it can read the
terminal, etc) but under some circumstances, zsh fails to put
some processes in that group, which is a bug.

$ </proc/self/stat awk '{print $5, $8}' >&2
127235 127235
$ </proc/self/stat awk '{print $5, $8; system("exec sleep 1")}'  >&2 | ps -o pid,pgid,comm
131569 131569
    PID    PGID COMMAND
 124948  124948 zsh
 131569  131569 awk
 131570  131569 ps
 131571  131569 sleep
$ </proc/self/stat awk '{print $5, $8}' >&2 | { :; }
127410 127410
$ </proc/self/stat awk '{print $5, $8}' >&2 | { : | :; }
127496 124948

In that latter case, awk is in a different process group
(127496) from the terminal foreground process group (124948
which here is the process group of the main shell process!).

-- 
Stephane