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From: Vincent Lefevre <vincent@vinc17.net>
To: zsh-users@zsh.org
Subject: Re: kill the LHS command of a pipe once the RHS command terminates
Date: Mon, 29 Jul 2019 22:48:57 +0200	[thread overview]
Message-ID: <20190729204857.GA28524@zira.vinc17.org> (raw)
In-Reply-To: <CAH+w=7a8aBsxdF1Otwvbm7eWe=BC2T0Ny87j+sY5QW7oXM=j_Q@mail.gmail.com>

On 2019-07-29 08:54:19 -0700, Bart Schaefer wrote:
> On Mon, Jul 29, 2019 at 8:24 AM Vincent Lefevre <vincent@vinc17.net> wrote:
> >
> > On 2019-06-28 13:04:30 +0200, Vincent Lefevre wrote:
> > >
> > > zira% head -n 1 <(echo foo; sleep 3; echo err >&2)
> > > foo
> >
> > Another issue is that if the producer side tries to access the terminal
> > (e.g. ssh, for a passphrase), all the processes of this side are stopped
> > due to a SIGTTOU signal.
> 
> Even if they weren't stopped by TTOU, they'd almost certainly be
> stopped by TTIN.

Yes.

> > Concerning the documentation, the zshexpn(1) man page does not say
> > that a process in process substitution is run in background.
> 
> They have to be, otherwise either you'd need unlimited buffering or
> the read of the descriptor could deadlock.

I don't see how this is related to buffering. This would be the same
case as with a pipe (cmd1 | cmd2), for which both commands run in
foreground and there are no buffering issues.

> If you want it run in the foreground, use =(...).

That's not OK, because the main command is started only when
the =(...) command terminates:

zira% echo =(echo a; sleep 3; echo b)

gives its output (the temporary file) only after 3 seconds. And even
without this problem, I'm not sure that this would work with a pager,
as it would think that once a EOF has occurred, there is no more
output.

> > Later there's a mention of it being run asynchronously, but this
> > term has never been defined.
> 
> In the JOBS section:
> 
>        If the MONITOR option is set, an interactive shell associates
>        a job with each pipeline. It keeps a table of current jobs,
>        printed by the jobs command, and assigns them small integer
>        numbers. When a job is started asynchronously with `&', the
>        shell prints a line to standard error which looks like:
[...]

As described, the "asynchronously" concerns only jobs started with "&".
BTW, there is nothing in the job table:

zira% echo <(sleep 3); jobs
/proc/self/fd/11
zira%

> And then in the SIGNALS section:
> 
>        Certain jobs are run asynchronously by the shell other than
>        those explicitly put into the background;

It says that jobs explicitly put into the background are run
asynchronously, but nothing about the converse.

-- 
Vincent Lefèvre <vincent@vinc17.net> - Web: <https://www.vinc17.net/>
100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/>
Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)

  reply	other threads:[~2019-07-29 20:49 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-28 11:04 Vincent Lefevre
2019-06-28 11:38 ` Vincent Lefevre
2019-06-29 16:17 ` Bart Schaefer
2019-07-06 23:55   ` Vincent Lefevre
2019-07-07  4:54     ` Bart Schaefer
2019-07-09 10:08       ` Vincent Lefevre
2019-07-09 10:54         ` Vincent Lefevre
2019-07-29 15:23 ` Vincent Lefevre
2019-07-29 15:54   ` Bart Schaefer
2019-07-29 20:48     ` Vincent Lefevre [this message]
2019-07-30  0:00       ` Bart Schaefer
2019-07-30  0:17         ` Vincent Lefevre
     [not found] <20190628110430.GA13790__36317.6205357135$1561719956$gmane$org@zira.vinc17.org>
2019-06-28 18:41 ` Stephane Chazelas
2019-06-29  1:24   ` Vincent Lefevre
2019-06-29 15:30     ` Stephane Chazelas
2019-07-06 23:49       ` Vincent Lefevre
2019-07-29 23:08         ` Vincent Lefevre
2019-07-29 23:15           ` Vincent Lefevre
2019-07-29 23:42             ` Bart Schaefer
2019-07-30  0:40               ` Vincent Lefevre

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