From: Eli Zaretskii <eliz@gnu.org>
To: Daniel Mendler <mail@daniel-mendler.de>
Cc: 48118@debbugs.gnu.org
Subject: bug#48118: 27.1; 28; Only first process receives output with multiple running processes
Date: Fri, 30 Apr 2021 18:58:06 +0300 [thread overview]
Message-ID: <83bl9vbw8h.fsf@gnu.org> (raw)
In-Reply-To: <a190b936-eb10-c9ab-89b1-cbb8bd969650@daniel-mendler.de> (message from Daniel Mendler on Fri, 30 Apr 2021 17:39:35 +0200)
> Cc: 48118@debbugs.gnu.org
> From: Daniel Mendler <mail@daniel-mendler.de>
> Date: Fri, 30 Apr 2021 17:39:35 +0200
>
> >> Which scenarios break?
> >
> > For example, if the filter function call accept-process-output. Or
> > does anything else that changes output from which processes is or
> > isn't available.
>
> Does this necessarily prevent scheduling? I interpret
> `accept-process-output` as a function which prioritizes a process, but I
> am unsure if this makes it impossible to implement additional scheduling.
A call to accept-process-output prioritizes a process only if it
explicitly requests output from that single process. Which is not
necessarily true in all cases.
> > What does this mean, exactly? Which quantity should be doled in a
> > round-robin fashion? bytes read from the processes? something else?
> >
> > If the bytes read, then how do you suggest to handle two processes
> > which produce output at very different rates?
>
> For example bytes read or time spent to handle a process (time spent in
> the filter function?).
Bytes read has a problem when processes produce output a very
different rates. Time spent to handle may (and usually does) mean the
filter function does something expensive, it doesn't necessarily tell
anything about the output from the subprocess.
> When I stumbled over this issue, it astonished me that Emacs
> does not seem to do any scheduling at all and handles only a single
> process.
If you read the code, you will see this isn't what happens. What
happens is that Emacs reads a chunk of output from the first process
it sees ready, then it goes back and re-checks which processes are
ready -- and in your scenario I think it again sees that the first
process is ready.
> What is the reason for the current behavior? Is it predictability? If I
> understand correctly, Emacs always reads from the first process. If data
> arrives, Emacs does not read from the second processes at all. Only if
> no data is available from the first process, the second process is
> handled. Is it like this?
In your scenario, yes. It depends on how large is the output produced
by a process in one go.
I suggest to read the code of wait_reading_process_output, it has some
non-trivial logic in this department.
next prev parent reply other threads:[~2021-04-30 15:58 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-30 13:44 bug#48118: 27.1; 28; Only first process receives output with multiple running processes Daniel Mendler
2021-04-30 14:17 ` Eli Zaretskii
2021-04-30 14:23 ` Daniel Mendler
2021-04-30 14:31 ` Eli Zaretskii
2021-04-30 14:26 ` Eli Zaretskii
2021-04-30 14:30 ` Daniel Mendler
2021-04-30 14:34 ` Eli Zaretskii
2021-04-30 14:45 ` Daniel Mendler
2021-04-30 14:59 ` Eli Zaretskii
2021-04-30 15:39 ` Daniel Mendler
2021-04-30 15:58 ` Eli Zaretskii [this message]
2021-04-30 16:17 ` Daniel Mendler
2021-04-30 18:06 ` Eli Zaretskii
2021-05-02 7:23 ` Lars Ingebrigtsen
2021-05-24 21:05 ` miha--- via Bug reports for GNU Emacs, the Swiss army knife of text editors
2021-05-25 11:38 ` Eli Zaretskii
2021-05-25 15:18 ` miha--- via Bug reports for GNU Emacs, the Swiss army knife of text editors
2021-05-25 17:12 ` Eli Zaretskii
2021-05-25 18:02 ` miha--- via Bug reports for GNU Emacs, the Swiss army knife of text editors
2021-05-25 19:02 ` Lars Ingebrigtsen
2021-06-04 13:34 ` Philipp
2021-06-04 14:00 ` Eli Zaretskii
2021-04-30 16:15 ` jakanakaevangeli
2021-04-30 17:52 ` Eli Zaretskii
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